Association between undervaccination with diphtheria, tetanus toxoids, and acellular pertussis (DTaP) vaccine and risk of pertussis infection in children 3 to 36 months of age

Vaccination Timeliness Among US Children Aged 0-19 Months, National Immunization Survey-Child 2011-2021

Importance

Delays in receiving vaccinations lead to greater vaccine-preventable disease risk. Timeliness of receipt of recommended vaccinations is not routinely tracked in the US, either overall or for populations that have known barriers to accessing routine health care, including lower-income families and children.

Objective

To measure vaccination timeliness among US children aged 0 to 19 months, overall and by socioeconomic indicators.

Design, Setting, and Participants

This serial, cross-sectional study analyzed nationally representative data from the 2011 to 2021 National Immunization Survey-Child (NIS-Child), an annual survey of parents, with immunization histories collected from clinicians administering vaccines. The 2020 and 2021 surveys largely reflected vaccinations in the US before the COVID-19 pandemic. Study participants included US children surveyed at ages 19 to 35 months. Data were analyzed from January to August 2023.

Exposure

Survey year.

Main Outcomes and Measures

The primary outcomes were average days undervaccinated (ADU) and percentage of children who received all vaccine doses on time (ie, 0 days undervaccinated) for the combined 7-vaccine series up to age 19 months. The mean adjusted annual change in on-time vaccination by socioeconomic indicators was calculated by use of multivariable log-linked binomial regression models.

Results

The surveys included 179 154 children (92 248 boys [51.2%]); 74 479 (31.4%, weighted) lived above the federal poverty level with more than $75 000 in annual family income, 58 961 (32.4%) lived at or above the poverty level with $75 000 or less in annual family income, and 39 564 (30.2%) lived below the poverty level. Overall, the median (IQR) ADU for the combined 7-vaccine series in the US decreased from 22.3 (0.4-71.5) days in the 2011 survey to 11.9 (0.0-55.5) days in the 2021 survey. The prevalence of on-time receipt of the combined 7-vaccine series increased from 22.5% (95% CI, 21.4%-23.6%) to 35.6% (95% CI, 34.2%-37.0%). Although children with more than $75 000 in annual family income had a 4.6% (95% CI, 4.0%-5.2%) mean annual increase in on-time vaccination, the mean annual increase was 2.8% (95% CI, 2.0%-3.6%) for children living at or above the poverty level with $75 000 or less in annual family income and 2.0% (95% CI, 1.0%-3.0%) for children living below the poverty level.

Conclusions and Relevance

In this cross-sectional study of NIS-Child data, improvements in vaccination timeliness were observed from the 2011 to the 2021 survey. However, widening disparities by socioeconomic indicators signal that increased efforts to facilitate timely vaccination among children in lower-income families are needed.

Attitudes Toward Routine Vaccines and COVID-19 Vaccines Among Parents of Infants and Toddlers in an Urban Safety-Net Setting

This study explores attitudes toward diphtheria-tetanus-acellular pertussis (DTaP), measles-mumps-rubella (MMR), influenza, and coronavirus disease 2019 (COVID-19) vaccines among English-speaking and Spanish-speaking parents of infants in a safety-net setting. Parents aged 18 years or older were recruited from outpatient clinics between December 2020 and December 2021. The interviews were then recorded, transcribed, translated, and qualitatively analyzed using the modified grounded theory. Thirty-two individuals participated (18 English-speaking and 14 Spanish-speaking). Almost all supported receiving routine childhood vaccines, DTaP, influenza, and MMR and believed that vaccines promote health. Vaccine concerns differed by each vaccine. Few participants expressed concerns about DTaP and MMR vaccines. Concerns around influenza vaccines often stemmed from personal experience and perceived increased risk of flu-like illnesses. Participants expressed the most concerns related to COVID-19 vaccinations, including age-based immunity of their infants. Based on these findings, future interventions to improve vaccine uptake may focus on benefits common to all vaccines, while addressing vaccine-specific concerns.

MA, Tovar-Rosero YY, Oñate AA, O'Ryan M. Two centuries of vaccination: historical and conceptual approach and future perspectives

Over the past two centuries, vaccines have been critical for the prevention of infectious diseases and are considered milestones in the medical and public health history. The World Health Organization estimates that vaccination currently prevents approximately 3.5-5 million deaths annually, attributed to diseases such as diphtheria, tetanus, pertussis, influenza, and measles. Vaccination has been instrumental in eradicating important pathogens, including the smallpox virus and wild poliovirus types 2 and 3. This narrative review offers a detailed journey through the history and advancements in vaccinology, tailored for healthcare workers. It traces pivotal milestones, beginning with the variolation practices in the early 17th century, the development of the first smallpox vaccine, and the continuous evolution and innovation in vaccine development up to the present day. We also briefly review immunological principles underlying vaccination, as well as the main vaccine types, with a special mention of the recently introduced mRNA vaccine technology. Additionally, we discuss the broad benefits of vaccines, including their role in reducing morbidity and mortality, and in fostering socioeconomic development in communities. Finally, we address the issue of vaccine hesitancy and discuss effective strategies to promote vaccine acceptance. Research, collaboration, and the widespread acceptance and use of vaccines are imperative for the continued success of vaccination programs in controlling and ultimately eradicating infectious diseases.

Pertussis immunisation strategies to optimise infant pertussis control: A narrative systematic review

OBJECTIVE

Countries routinely offering acellular pertussis vaccine, where long-term protection is not sustained, have the challenge of selecting an optimal schedule to minimise disease among young infants. We conducted a narrative systematic review and synthesis of information to evaluate different pertussis immunisation strategies at controlling pertussis disease, hospitalisation, deaths, and vaccine effectiveness among young infants.

METHODS

We conducted a review of the literature on studies about the primary, booster, and/or maternal vaccination series and synthesised findings narratively. Countries offering the first three doses of vaccine within six-months of life and a booster on or before the second year or life were defined as accelerated primary and booster schedules, respectively. Countries offering primary and booster doses later were defined as extended primary and booster schedules. All search results were screened, and articles reviewed and reconciled, by two authors. The Risk of Bias in Non-randomised Studies of Intervention tool was used to evaluate the risk of bias.

FINDINGS

A total of 98 studies were included in the analyses and the following recurring themes were described: timing of vaccination, vaccine coverage, waning immunity/vaccine effectiveness, direct and indirect effectiveness, switching from an accelerated to extended schedule, impact of changes in testing. The risk of bias was generally low to moderate for most studies.

CONCLUSION

Comparing schedules is challenging and there was insufficient evidence to that one schedule was superior to another. Countries must select a schedule that maintains high vaccine coverage and reduced the risk of delaying the delivery vaccines to protect infants.

Failure to Complete Multidose Vaccine Series in Early Childhood

BACKGROUND

Most early childhood immunizations require 3 to 4 doses to achieve optimal protection. Our objective was to identify factors associated with starting but not completing multidose vaccine series.

METHODS

Using 2019 National Immunization Survey-Child data, US children ages 19 to 35 months were classified in 1 of 3 vaccination patterns: (1) completed the combined 7-vaccine series, (2) did not initiate ≥1 of the 7 vaccine series, or (3) initiated all series, but did not complete ≥1 multidose series. Associations between sociodemographic factors and vaccination pattern were evaluated using multivariable log-linked binomial regression. Analyses accounted for the survey's stratified design and complex weighting.

RESULTS

Among 16 365 children, 72.9% completed the combined 7-vaccine series, 9.9% did not initiate ≥1 series, and 17.2% initiated, but did not complete ≥1 multidose series. Approximately 8.4% of children needed only 1 additional vaccine dose from 1 of the 5 multidose series to complete the combined 7-vaccine series. The strongest associations with starting but not completing multidose vaccine series were moving across state lines (adjusted prevalence ratio [aPR] = 1.45, 95% confidence interval [CI]: 1.18-1.79), number of children in the household (2 to 3: aPR = 1.29, 95% CI: 1.05-1.58; 4 or more: aPR = 1.68, 95% CI: 1.30-2.18), and lack of insurance coverage (aPR = 2.03, 95% CI: 1.42-2.91).

CONCLUSIONS

More than 1 in 6 US children initiated but did not complete all doses in multidose vaccine series, suggesting children experienced structural barriers to vaccination. Increased focus on strategies to encourage multidose series completion is needed to optimize protection from preventable diseases and achieve vaccination coverage goals.

The association between vaccine hesitancy and pertussis: a systematic review and meta-analysis

BACKGROUND

Robust routine immunization schedules for pertussis-containing vaccines have been applied for years, but pertussis outbreaks remain a worldwide problem. This study aimed to investigate the association between vaccine hesitancy and pertussis in infants and children.

METHODS

We searched PubMed, Cochrane, Web of Science, Embase, and China National Knowledge Internet for studies published between January 2012 and June 2022. This study included case-control and cohort studies that assessed the association between childhood/maternal vaccine hesitancy and odds ratios (ORs), risk ratios (RRs), and vaccine effectiveness (VE) related to pertussis in infants and children [Formula: see text] 9 years old. ORs/VEs with a 95% confidence interval (CI) were calculated. Random-effects meta-analysis models were used for appropriate pooled estimates, and heterogeneity was assessed using [Formula: see text]. Cumulative meta-analysis and subgroup analyses stratified by study characteristics were performed.

RESULTS

Twenty-two studies were included, with a mean quality score of 7.0 (range 6.0-9.0). Infants and children with pertussis were associated with higher vaccine hesitancy to all doses (OR = 4.12 [95% CI: 3.09-5.50]). The highest OR was between children who were unvaccinated over four doses and children who were fully vaccinated (OR = 14.26 [95%CI: 7.62-26.70]); childhood vaccine delay was not statistically significantly associated with pertussis risk (OR = 1.18 [95% CI: 0.74-1.89]). Maternal vaccine hesitancy was associated with significantly higher pertussis risk in infants aged 2 and 3 months old, with higher pertussis ORs in infants [Formula: see text] 2 months old (OR = 6.02 [95%CI: 4.31-8.50], OR = 5.14 [95%CI: 1.95-13.52] for infants [Formula: see text] 2 and [Formula: see text] 3 months old, respectively). Maternal and childhood VEs were high in reducing pertussis infection in infants and children. The administration time of maternal vaccination had little effect on VE.

CONCLUSION

Vaccine hesitancy increased pertussis risks in infants and children. Ensuring that children receive up-to-date pertussis vaccines is essential; short delays in receiving childhood vaccinations may be unimportant. Maternal vaccinations for pertussis should be encouraged.

Characteristics of Oklahoma Pediatricians Who Dismiss Families for Refusing Vaccines

Vaccine refusal is increasing. Objectives were to assess frequency of declining or dismissing patients who refuse vaccines, which vaccine(s) prompt pediatricians to decline/dismiss patients, and demographics of pediatricians who decline/dismiss patients. Active members of the Oklahoma American Academy of Pediatricians (AAP) were surveyed. Chi-square tests with non-overlapping 95% confidence intervals compared proportions of providers across various metrics. In all, 47% (48/103) versus 35% (34/98) reported declining versus dismissing patients for refusing vaccines, respectively. Pediatricians were unlikely to decline/dismiss patients if they refused influenza, human papilloma virus (HPV), or MenB vaccines. Pediatricians with more years in practice were less likely to decline 15% (9/62) versus 44% (16/36), P = 0.002 and dismiss 8% (5/62) versus 33% (12/36), P = 0.002 patients. Rural pediatricians were less likely than urban to decline 12% (2/17) versus 29% (26/89), P = NS and dismiss patients 0% (0/17) versus 21% (19/89), P = 0.04. Dismissing/declining patients for vaccine refusal is more common among Oklahoma pediatricians than nationally reported. Patterns differ by practice setting, years in practice, and specific vaccine refused.

Burden of pertussis among young infants in Malaysia: A hospital-based surveillance study

BACKGROUND

The case fatality rate and the risk of complications due to pertussis is very high in infants. Asia has the second highest childhood pertussis burden. The study aimed to assess the prevalence, clinical complications, and mortality rates of pertussis disease requiring hospitalization among young infants in Malaysia.

METHODS

The study was a one-year, hospital-based, multi-site surveillance of infants less than six months of age with symptoms consistent with pertussis and a cross-sectional analysis of their mothers for recent pertussis infection. Information was obtained from medical records and interviews with the parents. Pertussis diagnosis was confirmed for all infants through serum anti-PT titration test or PCR test.

RESULTS

441 possible cases of pertussis were included in this study. Of these, 12.7 % had laboratory confirmation of pertussis. Infants with confirmed pertussis had significantly higher rates of cyanosis (37.5 % vs 8.6 %; p < 0.0001) and apnea (12.5 % vs 3.9 %; p = 0.027) than test-negative infants. Most infants from both groups were in recovery/recovered at discharge. Those with confirmed pertussis had higher case fatality rate than test-negative cases (5.4 % vs 1.0 %; p = 0.094), but the difference did not reach significance. The majority of confirmed pertussis cases (89.3 %) occurred in infants too young to be fully vaccinated or under-vaccinated for their age. Both test-negative and confirmed pertussis resulted in work-day losses and incurred costs for both parents.

CONCLUSIONS

A high pertussis disease burden persists in infants less than six months of age, especially among those un- and under-vaccinated. Maternal and complete, on-time infant vaccination is important to reduce disease burden.

Evaluating vaccination coverage and timeliness in American Indian/Alaska Native and non-Hispanic White children using state immunization information system data, 2015-2017

Comprehensive estimates of vaccination coverage and timeliness of vaccine receipt among American Indian/Alaska Native (AI/AN) children in the United States are lacking. This study’s objectives were to quantify vaccination coverage and timeliness, as well as the proportion of children with specific undervaccination patterns, among AI/AN and non-Hispanic White (NHW) children ages 0–24 months in Montana, a large and primarily rural U.S. state. Data from Montana’s immunization information system (IIS) for children born 2015–2017 were used to calculate days undervaccinated for all doses of seven recommended vaccine series. After stratifying by race/ethnicity, up-to-date coverage at key milestone ages and the proportion of children demonstrating specific patterns of undervaccination were reported. Among n = 3,630 AI/AN children, only 23.1% received all recommended vaccine doses on-time (i.e., zero days undervaccinated), compared to 40.4% of n = 18,022 NHW children (chi-square p < 0.001). A greater proportion of AI/AN children were delayed at each milestone age, resulting in lower overall combined 7-vaccine series completion, by age 24 months (AI/AN: 56.6%, NHW: 64.3%, chi-square p < 0.001). As compared with NHW children, a higher proportion of AI/AN children had undervaccination patterns suggestive of structural barriers to accessing immunization services and delayed starts to vaccination. More than three out of four AI/AN children experienced delays in vaccination or were missing doses needed to complete recommended vaccine series. Interventions to ensure on-time initiation of vaccine series at age 2 months, as well initiatives to encourage completion of multi-dose vaccine series, are needed to reduce immunization disparities and increase vaccination coverage among AI/AN children in Montana.

Barriers to and facilitators of early childhood immunization in rural areas of the United States: a systematic review of the literature

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Early childhood vaccination coverage is low in rural areas of the United States.

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Reminder-recall & positive family-provider relationships facilitate vaccine uptake.

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Parental hesitancy is a barrier to early childhood vaccination in the rural U.S.

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Vaccine referrals & distance to providers are also rural-specific barriers.

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To increase vaccine coverage, interventions across rural populations are needed.

Early childhood vaccination rates are lower in rural areas of the U.S. compared with suburban and urban areas. Our aim was to identify barriers to and facilitators of early childhood immunization in rural U.S. communities. We completed a systematic review of original research conducted in the U.S. between January 1, 2000-July 25, 2021. We searched PubMed, Cumulative Index for Nursing and Allied Health Literature, and Web of Science. We included studies that examined barriers to and facilitators of routine immunizations in children <36 months old in rural areas. Following the Preferred Reporting Items for Systematic Reviews and Meta-analyses guidelines, we reported studies’ methodologies and targeted populations, definitions of rurality, and common themes across studies that reflected barriers to or facilitators of vaccination. Ultimately, 17 papers met inclusion criteria for review. The majority of studies (10/17) were conducted within one U.S. state, and the same number (10/17) were conducted prior to 2005. Facilitators of vaccine uptake in rural communities identified across studies included reminder/recall systems and parents’ relationships with providers. Parental hesitancy, negative clinic experiences, referrals outside of primary care settings, and distance to providers were identified as barriers to vaccination in rural settings. This review revealed a limited scope of evidence on barriers to and facilitators of early childhood immunization in rural communities. More investigations of the causes of low vaccine coverage and the effectiveness of interventions for increasing vaccine uptake are urgently needed in rural pediatric populations to address persistent rural–urban immunization disparities.

Vaccine Administration in Children's Hospitals

OBJECTIVES

To examine inpatient vaccine delivery across a national sample of children's hospitals.

METHODS

We conducted a retrospective cohort study examining vaccine administration at 49 children's hospitals in the Pediatric Health Information System database. Children <18 years old admitted between July 1, 2017, and June 30, 2019, and age eligible for vaccinations were included. We determined the proportion of hospitalizations with ≥1 dose of any vaccine type administered overall and by hospital, the type of vaccines administered, and the demographic characteristics of children who received vaccines. We calculated adjusted hospital-level rates for each vaccine type by hospital. We used logistic and linear regression models to examine characteristics associated with vaccine administration.

RESULTS

There were 1 185 667 children and 1 536 340 hospitalizations included. The mean age was 5.5 years; 18% were non-Hispanic Black, and 55% had public insurance. There were ≥1 vaccine doses administered in 12.9% (95% confidence interval: 12.8-12.9) of hospitalizations, ranging from 1% to 45% across hospitals. The most common vaccines administered were hepatitis B and influenza. Vaccine doses other than the hepatitis B birth dose and influenza were administered in 1.9% of hospitalizations. Children had higher odds of receiving a vaccine dose other than the hepatitis B birth dose or influenza if they were <2 months old, had public insurance, were non-Hispanic Black race, were medically complex, or had a length of stay ≥3 days.

CONCLUSIONS

In this national study, few hospitalizations involved vaccine administration with substantial variability across US children's hospitals. Efforts to standardize inpatient vaccine administration may represent an opportunity to increase childhood vaccine coverage.

Immunization practices and risk of anaphylaxis: a current update, comprehensive of COVID-19 vaccination data

PURPOSE OF REVIEW

This review aims to provide an updated report in regards to the correlation between vaccines and anaphylaxis and the related risk in the population.

RECENT FINDINGS

Initial reports showed higher incidence of anaphylaxis following messenger RNA COVID-19 vaccines compared with 'routine' vaccinations, likely influenced by the great attention paid to these 'new' vaccines. However, anaphylaxis has still to be considered quite rare and its incidence will be systematically reconsidered in the light of additional data collected.

SUMMARY

Adverse reactions to vaccines are commonly reported but most of them are nonspecific mild events, whereas vaccine-related anaphylaxis is considered a rare event, with an incidence rate equal to 1.3 cases per million vaccine doses administered. As anaphylaxis reports usually start to be reported to passive pharmacovigilance during postmarketing surveillance, the first data are used to be influenced by under- and over-reporting and lack of denominators and following studies are needed to confirm the causal relationship. This might create an initial overcautiously approach to new immunization practices but, being anaphylaxis a potential life-threatening event, every suspected contraindication has to be deepened to maximize effectiveness and safety profile and constantly redefined not to exclude an overestimated population group who could receive the vaccine uneventfully.

Duration of protection against Bordetella pertussis infection elicited by whole-cell and acellular vaccine priming in Polish children and adolescents

BACKGROUND

In the context of reported resurgence of pertussis in the last decade, researchers hypothesized that acellular (aP) pertussis vaccines elicit a shorter-lived protection compared to whole-cell (wP) pertussis vaccines. However, in the studies seeking to demonstrate this hypothesis, exposure to each vaccine type was not concurrent, and contradictory epidemiologic modeling questioned its validity. The context of pertussis vaccination history in Poland, with both vaccine types used concurrently in comparable proportions, provided an opportunity to investigate this hypothesis. We sought to compare waning of protection by primary series vaccine type by measuring anti-pertussis toxin antibody concentrations as proxy for recent infection.

MATERIALS AND METHODS

Serological samples from 2,745 children and adolescents aged ≥5 years and <16 years and with completed 5-dose pertussis vaccination series were tested by ELISA for pertussis toxin (PT) antibodies. Participants were stratified by type of priming vaccine (wP or aP). Vaccination timeliness and priming-specific trends in anti-PT antibody levels by time since last vaccine dose were analyzed.

RESULTS

A total of 1,161 (42.5%) children received wP vaccines, and 1,314 (48.1%) received aP vaccines for their primary series and toddler booster. Overall, 53.57% of the subjects received doses 2-4 in a timely manner, while only 41.52% received all 5 doses at the recommended intervals. Using GMCs or seropositivity measures, both priming groups showed a re-increase in anti-PT antibody levels signing infection in recent years from 8 years after the school-entry booster onward. Comparisons did not show any significant differences between the two groups in the timing or intensity of this re-increase.

CONCLUSION

Our results clearly confirm that vaccine-elicited immunity against pertussis wanes among adolescents even after a complete infant, toddler and school-entry vaccination series. The timing and intensity of the waning of protection appear similar with whole-cell as with acellular pertussis vaccines.

Improving Vaccination for Young Children (IVY): A Stepped-Wedge Cluster Randomized Trial

BACKGROUND

High childhood vaccination rates are critical for public health. We hypothesized that implementation of a vaccine education and quality improvement (QI) program, Improving Vaccinations for Young Children (IVY), would improve childhood vaccine rates.

METHODS

Eight pediatric practices (3 academic-based, 5 community-based) were randomized to implement IVY within a stepped-wedge cluster randomized trial (SWCRT) in middle Tennessee. Two educational modules on vaccines were developed using best practices in instructional design. Modules were provided electronically and were tailored to providers or office staff. Practices completed in-person QI coaching sessions and selected at least 2 vaccination-related QI changes. Data were collected monthly. The primary analysis examined intervention effect on the primary outcome of Combination 10 vaccination status for children who turned 2 in the previous month. Combination 10 status without influenza vaccine was a secondary outcome, and exploratory analyses assessed intervention effects after adjusting for time and practice type.

RESULTS

Data from 4041 patients (1788 control; 2253 intervention) were collected. The intervention effect was not significant on the primary outcome (OR = 1.01; 95% CI [0.76, 1.34]; P > .9), however there were positive intervention effects in secondary and exploratory models analyzing Combination10 rates without flu, including models adjusting for variation over time (0.20; 95% CI [0.04,0.35]; P = .01) and practice type (higher vaccination rate in academic practices, 0.23; 95% CI [0.03,0.42]; P = .03).

CONCLUSIONS

Combination 10 rates were not significantly improved with IVY, yet evidence of beneficial effect on rates without flu vaccine was found. Future studies could evaluate effects over a longer time period and within a larger practice sample.

Association of Diphtheria-Tetanus-Acellular Pertussis Vaccine Timeliness and Number of Doses With Age-Specific Pertussis Risk in Infants and Young Children

IMPORTANCE

In most countries, the diphtheria-tetanus-acellular pertussis (DTaP) vaccine is administered as a 3-dose infant series followed by additional booster doses in the first 5 years of life. Short-term immunity from the DTaP vaccine can depend on the number, timing, and interval between doses. Not receiving doses in a timely manner might be associated with a higher pertussis risk.

OBJECTIVE

To examine the association between number and timeliness of vaccine doses and age-specific pertussis risk.

DESIGN, SETTING, AND PARTICIPANTS

This population-based, retrospective cohort study used Washington State Immunization Information System data and pertussis surveillance data from Public Health Seattle and King County, Washington. Included participants were children aged 3 months to 9 years born or living in King County, Washington, between January 1, 2008, and December 31, 2017. Data were analyzed from June 30 to December 1, 2019.

EXPOSURES

Being undervaccinated (receiving fewer than recommended doses at a given age) or delayed vaccination (not receiving doses within time frames recommended by Centers for Disease Control and Prevention).

MAIN OUTCOMES AND MEASURES

Suspected, probable, and confirmed pertussis diagnosis.

RESULTS

A total of 316 404 children (median age, 65.2 months [interquartile range, 35.3-94.1 months]; 162 025 boys [51.2%]) as of December 31, 2017, with 17.4 million person-months of follow-up were included in the analysis. A total of 19 943 children (6.3%) had no vaccines recorded in the Immunization Information System, 116 193 (36.7%) received a vaccine with a delay, and 180 268 (56.9%) were fully vaccinated with no delay. Delayed vaccination and undervaccination rates were higher for older children (17.6% delayed or undervaccinated at age 2 months for dose 1 at 3 months vs 41.6% at age 5 years for dose 5) but improved for successive birth cohorts (52.2% for 2008 birth cohort vs 32.3% for 2017 birth cohort). Undervaccination was significantly associated with higher risk of pertussis for the 3-dose primary series (adjusted relative risk [aRR], 4.8; 95% CI, 3.1-7.6), the first booster (aRR, 3.2; 95% CI, 2.3-4.5), and the second booster (aRR, 4.6; 95% CI, 2.6-8.2). However, delay in vaccination among children who received the recommended number of vaccine doses was not associated with pertussis risk.

CONCLUSIONS AND RELEVANCE

The results of this cohort study suggest that undervaccination is associated with higher pertussis risk. Short delays in vaccine receipt may be less important if the age-appropriate number of doses is administered, but delaying doses is not recommended. Ensuring that children receive all doses of pertussis vaccine, even if there is some delay, is important.

Detecting adherence to the recommended childhood vaccination schedule from user-generated content in a US parenting forum

Vaccine hesitancy is considered as one of the leading causes for the resurgence of vaccine preventable diseases. A non-negligible minority of parents does not fully adhere to the recommended vaccination schedule, leading their children to be partially immunized and at higher risk of contracting vaccine preventable diseases. Here, we leverage more than one million comments of 201,986 users posted from March 2008 to April 2019 on the public online forum BabyCenter US to learn more about such parents. For 32% with geographic location, we find the number of mapped users for each US state resembling the census population distribution with good agreement. We employ Natural Language Processing to identify 6884 and 10,131 users expressing their intention of following the recommended and alternative vaccination schedule, respectively RSUs and ASUs. From the analysis of their activity on the forum we find that ASUs have distinctly different interests and previous experiences with vaccination than RSUs. In particular, ASUs are more likely to follow groups focused on alternative medicine, are two times more likely to have experienced adverse events following immunization, and to mention more serious adverse reactions such as seizure or developmental regression. Content analysis of comments shows that the resources most frequently shared by both groups point to governmental domains (.gov). Finally, network analysis shows that RSUs and ASUs communicate between each other (indicating the absence of echo chambers), however with the latter group being more endogamic and favoring interactions with other ASUs. While our findings are limited to the specific platform analyzed, our approach may provide additional insights for the development of campaigns targeting parents on digital platforms.

The importance and effectiveness of vaccines is generally high, but concerns toward vaccination contribute to eroding confidence in vaccination. Recently, alternative vaccination schedules are becoming popular as they allow parents to selectively delay or refuse certain vaccines depending on their specific concerns. Not being expressly anti-vaccination, these parents are challenging to identify on social media, however understanding the determinants of their hesitancy toward vaccines could help addressing parents’ concerns through targeted interventions. In this work, we create a Natural Language Processing pipeline to automatically identify parents who state their adherence to the recommended or alternative vaccination schedule on a popular parenting forum, BabyCenter US. We find that these users have distinct interests and different experiences with vaccination, although they frequently share similar sources of information (e.g., .gov websites). Differently from what is observed on most popular digital platforms like Facebook or Twitter, where users communicate mainly with like-minded users, Babycenter users communicate between each other independently of the vaccination schedule they adopt. These observations suggest that parenting fora may be a more suitable medium to develop intervention aiming to influence positively the vaccination behavior of parents.

Protective immune responses against Haemophilus influenza type b elicited by a fully-liquid DTaP-IPV-Hib-HepB vaccine (VAXELIS™)

BACKGROUND

DTaP-IPV-Hib-HepB is a fully-liquid, hexavalent combination vaccine (Vaxelis™) approved for vaccination against diphtheria, tetanus, pertussis, poliomyelitis, hepatitis B, and invasive disease due to Haemophilus influenzae type b (Hib). Hib capsular polysaccharide, polyribosylribitol phosphate (PRP), is conjugated to Neisseria meningitidis outer membrane protein complex (OMPC). Safety and immunogenicity of DTaP-IPV-Hib-HepB were evaluated in 6 Phase III clinical studies including > 5,200 children. Studies included vaccination schedules in the United States (2, 4, 6 months of age) and Europe (2, 3, 4, 12 months of age and 2,4,11-12 months of age).

METHODS

Data pertaining to anti-PRP responses of DTaP-IPV-Hib-Hep B compared to control vaccines from 5 Phase III studies are summarized.

RESULTS

Post-infant series, the percentage of participants that achieved protective antibody thresholds for PRP (anti-PRP titer ≥ 0.15 μg/mL and ≥ 1.0 μg/mL, respectively) were higher in DTaP-IPV-Hib-HepB recipients compared to recipients who received control vaccines. A high level of protective responses (96.6% at ≥ 0.15 μg/mL [95% CI:94.8, 97.9%]; 72.9% at ≥ 1.0 μg/mL [95% CI:69.2,76.4%]) were seen post-dose 2 of the 2 + 1 vaccination schedule and met superiority criteria over comparator, p-value < 0.001. In the same schedule, prior to administration of the toddler dose (in the second year of life), anti-PRP titers were higher in DTaP-IPV-Hib-HepB recipients (91.4% at ≥ 0.15 μg/mL; 46.8% at ≥ 1.0 μg/mL) as compared to recipients who received control vaccines (63.4% at ≥ 0.15 μg/mL; 17.1% at ≥ 1.0 μg/mL). One-month post-toddler dose, high levels of anti-PRP titers were achieved in both DTaP-IPV-Hib-HepB recipients (99.8% at ≥ 0.15 μg/mL; 96.6% at ≥ 1.0 μg/mL) and recipients who received control vaccines (99.5% at ≥ 0.15 μg/mL; 94.9% at ≥ 1.0 μg/mL).

CONCLUSIONS

These results support that DTaP-IPV-Hib-HepB induces a robust and sustained early Hib response. During the high-risk period for Hib disease after the infant vaccine and prior to the toddler dose; >90% of recipients maintained superior protective anti-PRP levels compared to control.

Prevalence and correlates of vaccine attitudes and behaviors in a cohort of low-income mothers

The US is facing a rise in vaccine hesitancy, delay, and refusal, though little is known about these outcomes in socio-economically disadvantaged populations. This study examines the prevalence and correlates of vaccine attitudes and behaviors in a diverse cohort of low-income mothers receiving home visiting services. Survey data were collected from 813 recipients of evidence-based home visiting services in Wisconsin from 2013 to 2018. Analyses were performed to describe outcome measures of vaccine attitudes and self-reported completion, and multivariate regressions were used to test associations between vaccine-related outcomes and hypothesized correlates. Most women (94%) reported their children were up to date on vaccines; 14.3% reported having ever delayed vaccination. A small minority disagreed that vaccines are important (5.0%), effective (5.4%), and safe (6.2%), though a larger proportion responded ambivalently (10.9%–21.9%). Participants with greater trust in health care providers reported more positive overall vaccine attitudes (B = 0.24; 95% CI = 0.17, 0.31), a lower likelihood of vaccine delay (OR = 0.57; 95% CI = 0.46, 0.73), and a greater likelihood of being up to date on vaccines (OR = 1.79, 95% CI = 1.30, 2.44). Women with greater trust in a home visitor also rated vaccines more positively (B = 0.09; 95% CI = 0.02, 0.15), and women who reported better mental health were more likely to report their children were up to date (OR = 1.05; 95% CI = 1.02, 1.09). Compared to non-Hispanic whites, American Indians and non-Hispanic blacks had poorer vaccine-related outcomes. More research on vaccine attitudes and behaviors among higher-risk populations is needed to develop tailored strategies aimed at addressing vaccine hesitancy and underimmunization.

The state of vaccine safety science: systematic reviews of the evidence

This Review updates the scientific evidence assessing possible causal associations of adverse events following immunisation (AEFI) compiled in the 2012 report from the Institute of Medicine and the 2014 report from the Agency for Healthcare Research and Quality. For 12 of 46 AEFI examined, a causal relationship has been established with at least one vaccine currently routinely recommended to the general USA population: anaphylaxis, arthralgia or arthritis (mild, acute, and transient, not chronic), deltoid bursitis (when vaccine is administered improperly), disseminated varicella infection (in immune deficient individuals for whom the varicella vaccine is contraindicated), encephalitis, febrile seizures, Guillain-Barré syndrome, hepatitis (in immune deficient individuals for whom the varicella vaccine is contraindicated), herpes zoster, immune thrombocytopenic purpura, meningitis, and syncope. Other than mild acute and transient arthralgia or arthritis, which is very common in adult women after rubella vaccine, these adverse reactions are rare or very rare. Vaccines have an excellent safety profile overall and provide protection against infectious diseases to individuals and the general population.

Characterizing the vaccine knowledge, attitudes, beliefs, and intentions of pregnant women in Georgia and Colorado

Vaccine coverage for maternal vaccines is suboptimal; only about half of pregnant women received influenza and Tdap vaccines in 2018. We explored knowledge, attitudes, beliefs, intentions, and trust regarding maternal and infant vaccines among pregnant women. Between June 2017 and July 2018, we surveyed 2196 pregnant women recruited from geographically and socio-demographically diverse prenatal care practices in Georgia and Colorado (56% response rate). Fifty-six percent of pregnant women intended to receive both influenza and Tdap vaccines during pregnancy and 68% intended to vaccinate their baby with all recommended vaccines on time. Attitudinal constructs associated with intention to vaccinate include confidence in vaccine safety (ORs: 16–38) and efficacy (ORs: 4–19), perceived risk of vaccine-preventable diseases (ORs: 2–6), social norms (ORs: 4–10), and trust in sources of vaccine information. Women pregnant with their first child were less likely than women who had prior children to intend to vaccinate themselves and their children, more likely to be unsure about their intentions to receive both maternal and infant vaccines, and less likely to report feeling they had enough knowledge or information about vaccines and vaccine safety (p < .01). This demonstrates an opportunity for vaccine education to increase vaccine confidence and informed decision-making, especially among first-time pregnant women.

Effects of California Assembly Bill 2109 in Low Vaccination Rate Counties: Are We Looking at the Right Variables?

OBJECTIVES

California Assembly Bill 2109 (AB2109) was passed in 2012 and restricted the obtainment of personal belief exemptions (PBEs) for vaccination requirements for school-aged children. This study examined changes in up-to-date (UTD) vaccination rates, PBEs, and conditionally accepted students (CASs) at 3 time points. The study also examined the association of PBEs and CASs on county and school immunization rates.

DESIGN

This study utilized 6 academic years of immunization data from all kindergartens in California from 2010-2011 to 2015-2016. The years were selected to include data 2 years prior to the introduction of the bill, 2 years prior to implementation, and 2 years after the new legislation went into effect in 2014. Data were analyzed for changes in variables over time at the state, county, and school levels. A Pearson correlation was performed to assess the association between CAS, PBE, and not-UTD rates in low- and high-UTD counties.

RESULTS

Counties with the highest percentage of unimmunized students have significantly higher mean CAS rates than PBE rates (P < .01 for all years). CASs were found to be more highly correlated with students not-UTD with immunizations than PBEs in all years studied (P < .01 for all years) and with far greater effect size in low-UTD counties (<90% UTD rate). There was a small rise in PBEs and a small reduction in UTD rates after AB2109 was signed but a fall in PBE and CAS rates and a rise in UTD rates postimplementation.

CONCLUSION

Many California counties have high levels of CASs at the time of kindergarten entry. The extent to which schools require CASs to complete required vaccinations is not known, which could contribute to the pool of undervaccinated students in California. Public health officials should be vigilant to ensure that schools follow up and enforce the completion of vaccines for conditionally admitted students. This study has policy implications due to the fact that it has been revealed that there is a large undervaccinated population remaining relatively unaccounted for in California despite recent efforts.

Vaccination Status and Resource Use During Hospital Visits for Respiratory Illnesses

OBJECTIVES

To evaluate variation in resource use for children with acute respiratory tract illness (ARTI) by vaccination status.

METHODS

We conducted a retrospective cohort study of children 0 to 16 years of age at 5 children's hospitals with 1 of 4 ARTI diagnoses (pneumonia, croup, asthma, and bronchiolitis) between July 2014 and June 2016. The predictor variable was provider-documented up-to-date (UTD) vaccination status (yes or no). Outcomes were receipt of each of the following tests or treatments (yes or no): complete blood cell count, blood cultures, C-reactive protein (CRP) level testing, viral testing, influenza testing, pertussis testing, chest radiographs, neck radiographs, antibiotics, and corticosteroids. We generated multivariable logistic regression models to examine the associations between our predictor and outcomes.

RESULTS

Of the 2302 participants included in analysis, 568 (25%) were diagnosed with pneumonia, 343 (15%) were diagnosed with croup, 653 (28%) were diagnosed with asthma, and 738 (32%) were diagnosed with bronchiolitis. Most (92%) vaccination statuses were documented as UTD. Across conditions, children whose vaccination status was documented as not UTD had higher adjusted odds of receiving a complete blood cell count, blood culture, CRP level testing, and influenza testing (P < .001). Children with pneumonia whose vaccination status was documented as not UTD had higher adjusted odds of receiving CRP level testing and influenza testing (P < .001). Children with croup whose vaccination status was documented as not UTD had higher adjusted odds of receiving blood cultures (P < .001).

CONCLUSIONS

Children with ARTI whose vaccination status was documented as not UTD had higher odds of undergoing laboratory testing compared with children whose vaccination status was documented as UTD.

Text message reminders to improve infant immunization in Guatemala: A randomized clinical trial

OBJECTIVE

Millions of infants worldwide remain under-immunized and at risk for unnecessary morbidity and mortality. Text messaging may offer a low-cost solution. We aimed to evaluate text message reminders to improve infant immunization in Guatemala.

METHODS

A randomized clinical trial was conducted at four public health clinics in rural and urban Guatemala. Infants ages six weeks to six months presenting for the first visit of the primary immunization series were randomly and equally allocated to an intervention or usual care group. Intervention participants were sent three text reminders before the second and third vaccine visits. The main outcome was timeliness of the second and third visits of the primary immunization series.

RESULTS

Of 1088 families approached for enrollment between March to November 2016, 871 were eligible and 720 (82.7%) participated; only 54 families did not own a cell phone. Due to country-wide vaccine shortages, visit completion was used as a proxy for overall immunization coverage. In intention to treat analysis, both intervention and usual care groups had high rates of visit completion, but intervention participants presented on the scheduled date more often (151 [42.2%] of 358 intervention vs. 111 [30.7%] of 362 usual care participants for visit 2, p = 0.001, and 112 [34.0%] of 329 intervention vs. 90 [27.0%] of 333 usual care participants for visit 3, p = 0.05). Intervention caregivers were significantly more likely to want to receive future text message reminders for vaccines and other appointments and were more willing to pay for these reminders.

CONCLUSION

Caregivers who were sent text message reminders in urban and rural Guatemala were less delayed for their child's immunization visits and reported high user satisfaction. Text message reminders may be an effective tool to increase infant vaccination coverage in low-income settings by reminding parents to vaccinate.

TRIAL REGISTRATION

NCT02567006 at clinicaltrials.gov.

Pertussis clinical case definition: Time for change in developing countries?

Background

Developing countries still struggle with late detection and mortality from pertussis. A review of clinical case definitions is necessary for early disease detection. This paper aimed to study possible clinical characteristics for earlier pertussis detection in a sporadic setting.

Methods

We conducted a retrospective review of medical and laboratory records in a general paediatric ward of a district hospital in a developing country. Inclusion criteria were all children hospitalised with nasopharyngeal swab taken for Bordetella pertussis. We compared sensitivity and specificity of World Health Organization diagnostic criteria with other clinical characteristics. Polymerase chain reaction Bordetella pertussis was the gold standard used.

Results

Out of 207 eligible admissions, the study retrieved 128 complete records. Approximately half of the children were less than 3 months old. The World Health Organization diagnostic criteria had a low sensitivity (15%), but high specificity (92%). In comparison, combinations that included paroxysmal cough, ill contact and facial congestion had higher sensitivity. Increasing cough duration improved specificity while compromising sensitivity.

Conclusion

Several clinical characteristics such as paroxysmal cough, facial congestion and a history of ill contact have potential for early clinical detection. Conventional emphasis on cough duration may hamper early detection.

Acellular Pertussis Vaccine Effectiveness Over Time

OBJECTIVES

To determine pertussis risk by diphtheria-tetanus-acellular pertussis (DTaP) vaccination status and time since last DTaP dose.

METHODS

Children born at Kaiser Permanente Northern California between 1999 and 2016 were followed from 3 months of age until they tested positive for pertussis; disenrolled from Kaiser Permanente Northern California; received the tetanus toxoid, reduced diphtheria toxoid, and acellular pertussis, adsorbed vaccine; turned 11 years of age, or the end of the study period. DTaP vaccination status was categorized on the basis of the number of doses received in relation to the number of doses expected according to the Advisory Committee on Immunization Practice-recommended ages.

RESULTS

Among 469 982 children ages 3 months to 11 years, we identified 738 pertussis cases. A total of 99 cases were unvaccinated, 36 were undervaccinated, 515 were fully vaccinated, and 88 were fully vaccinated plus 1 dose. Pertussis risk was 13 times higher among unvaccinated (adjusted hazard ratio [aHR] = 13.53; 95% confidence interval [CI] 10.64-17.21) compared with fully vaccinated children and 1.9 times higher (aHR = 1.86; 95% CI 1.32-2.63) among undervaccinated children. Among vaccinated children ages 19 to <84 months, pertussis risk was 5 times higher (aHR = 5.04; 95% CI 1.84-13.80) ≥3 years vs <1 year after vaccination. Among children ages 84 to 132 months, risk was 2 times higher (aHR = 2.32; 95% CI 0.97-5.59) ≥6 years vs <3 years after vaccination.

CONCLUSIONS

Undervaccinated and especially unvaccinated children were at greater risk of pertussis. However, most pertussis cases occurred among children age-appropriately vaccinated who were further away from their last DTaP dose, suggesting that suboptimal vaccine effectiveness played a major role in recent pertussis epidemics.

Pertussis Morbidity in Children 12-59 Months of Age: A NSW Public Health Network Study

BACKGROUND

Pertussis continues to be a significant public health problem despite high levels of vaccination. Although hospitalizations and deaths among children greater than 12 months of age are much less frequent than among infants less than 6 months of age, only limited information is available for this age group on other measures of morbidity.

METHODS

A cross-sectional study with a 6-week follow-up component was conducted in New South Wales, Australia in 2017 to measure morbidity among children 12-59 months of age notified to health authorities. Measures used included cough duration, cough severity, constitutional symptoms and impacts on the family. Associations between these outcomes and age group, vaccination status, asthma, treatment and family structure were explored.

RESULTS

Three hundred and five of 472 (65%) notified cases were interviewed at baseline with approximately 20% having a severe cough with no trend in prevalence across age groups. Forty-eight percent of cases had experienced 3 or more constitutional symptoms with rates significantly higher among younger children. Children who had received an 18-month booster vaccination were significantly less likely to experience 3 or more constitutional symptoms (odds ratio: 0.46, 95% confidence interval: 0.22-0.97). Fifty-one percent of cases were still coughing at 6 weeks. One-third of carers initially reported having disrupted sleep 4 or more nights per week with substantial disruption to carers' sleep still recorded at 6 weeks.

CONCLUSIONS

Substantial morbidity was observed in this age group with some evidence that the reintroduction of an 18-month acellular pertussis booster lessened disease severity.

Seroepidemiology of pertussis in Hangzhou, China, during 2009-2017

Objective: To delineate seroepidemiology of pertussis in Hangzhou, to evaluate the protection levels of pertussis among healthy populations, for improving prevention strategy of pertussis.Methods: During 2009-2017, a multistage stratified random sampling method was employed to select participants included via physical examination for subjects in several Community Health Centers in Hangzhou. Enzyme-Linked Immunosorbent Assay (ELISA) was used to detect Immunoglobulin G (IgG) antibodies against pertussis in serum samples. Results were compared among 11 age groups. Univariate and multivariate analysis were used to analyze the associations among the rates of pertussis IgG seropositivity and the geometric mean concentration (GMC) levels of pertussis IgG and the related factors.Results: A total of 3360 subjects with available information were included, with 1745 male and 1615 female. Of these, 59.6% subjects had a clear immunization history of diphtheria-tetanus-pertussis vaccine (DTP). The vaccination rates of DTP had a declined trend with older age. The rate of pertussis IgG seropositivity was 69.9% (95% confidence interval: 68.3-71.5) and the GMC for pertussis IgG was 48.46 U/ml. Significantly higher seropositivity and GMC for pertussis IgG were found in subjects that had inoculation vaccine history or unknown history when compared those without inoculation of vaccine, lower in age groups <10, 20-29, and 30-39 y when compared to the other age groups evaluated.Conclusions: There are different distribution profiles both of the seropositivity and GMC for pertussis IgG for different age groups and immunization history of vaccine groups. In order to prevent pertussis occurrence, it is important to employ a booster dose of pertussis vaccine in adolescents and adults.

Role of Evolutionary Selection Acting on Vaccine Antigens in the Re-Emergence of Bordetella Pertussis

Pertussis (“whooping cough”) is a re-emerging disease with increasing incidence among fully vaccinated individuals. We explored the genetic diversity of five Bordetella pertussis proteins used to generate the subunit vaccine across ancestral and newly emergent strains using immunoinformatics and evolutionary selection measurements. The five subunits of pertussis toxin (Ptx1–Ptx5) were highly conserved with regard to sequence, predicted structure, predicted antigenicity, and were under purifying selection. In contrast, the adhesin proteins pertactin (Prn) and filamentous hemagglutinin (FHA) were under statistically significant (p < 0.01) diversifying selection. Most heavily diversified sites of each protein fell within antigenic epitopes, and the functional adhesin motifs were conserved. Protein secondary structure was conserved despite sequence diversity for FHA but was changeable in Prn. These findings suggest that subunit vaccine-derived immunity does not impact Ptx1–Ptx5 but may apply evolutionary pressure to Prn and FHA to undergo diversifying selection. These findings offer further insight into the emergence of vaccine-resistant strains of B. pertussis.

Accuracy of Provider-Documented Child Immunization Status at Hospital Presentation for Acute Respiratory Illness

OBJECTIVES

To assess (1) the accuracy of child immunization status documented by providers at hospital presentation for acute respiratory illness and (2) the association of provider-documented up-to-date (UTD) status with immunization receipt during and after hospitalization.

METHODS

We conducted a retrospective cohort analysis of children ≤16 years old treated for asthma, croup, bronchiolitis, or pneumonia at a children's hospital between July 2014 and June 2016. Demographics, clinical characteristics, and provider-documented UTD immunization status (yes or no) at presentation were obtained from the medical record. We compared provider-documented UTD status to the gold standard: the child's UTD status as documented in the Washington State Immunization Information System (WAIIS). The sensitivity, specificity, and positive predictive value of provider-documented UTD status were calculated. We assessed the association of provider-documented UTD status and immunization during and within 30 days posthospitalization using multivariable logistic regression.

RESULTS

Among 478 eligible children, 450 (94%) had provider-documented UTD status at hospital presentation and an active WAIIS record. Overall, 92% and 42% were UTD by provider documentation and WAIIS records, respectively, with provider-documented UTD status having 98.4% sensitivity (95% confidence interval [CI]: 95.4%-99.7%), 12.2% specificity (95% CI: 8.5%-16.8%), and 44.6% positive predictive value (95% CI: 39.7%-49.5%). Per WAIIS records, 20% and 44% of children who were due for vaccines received a vaccine during or within 30 days posthospitalization, respectively. There was no significant association between provider-documented UTD status and immunization during or after hospitalization.

CONCLUSIONS

Provider-documented UTD immunization status at hospital presentation for children with respiratory illnesses overestimates UTD status, creating missed opportunities for immunization during and after hospitalization.

Age-appropriate compliance and completion of up to five doses of pertussis vaccine in US children

Background: In the United States (US), diphtheria, tetanus, and acellular pertussis (DTaP) vaccination is recommended at 2, 4, and 6 months (doses 1-3), 15-18 months (dose 4), and 4-6 years (dose 5). The objective of this study (GSK study identifier: HO-14-14383) was to examine DTaP completion and compliance rates among commercially insured and Medicaid-enrolled children. Secondarily, the study aimed at identifying predictors of compliance/completion. Methods: Truven Health MarketScan Commercial and Multi-State Medicaid databases (2005-2013) were analyzed separately. Children born during 2005-2011 with ≥ 2 years continuous enrollment from birth provided data for doses 1-4; those with continuous enrollment from birth to their seventh birthday provided dose 5 data. Series compliance (each recommended dose by 3, 5, and 7 months; 19 months; seventh birthday) and completion (3 doses by 8 months; 4 by 24 months; 5 by seventh birthday) were calculated. Predictors of compliance/completion were identified using multivariable logistic regression. Results: A total of 367,493 commercially insured and 766,153 Medicaid-enrolled children were followed for ≥ 2 years; and 23,574 and 41,284, respectively, for ≥ 7 years. Series compliance to doses 1-3, 1-4, and 1-5 were 67.2%, 55.3%, 47.5% (commercial) and 37.4%, 27.3%, 14.4% (Medicaid), respectively. Predictors of better compliance/completion included: later birth year (commercial/Medicaid) and higher household income (commercial); predictors of worse compliance/completion included: Northeast residence (commercial), birth hospitalization ≥ 14 days (commercial/Medicaid), and Black race/ethnicity (Medicaid). Conclusions: DTaP series compliance/completion improved over time, but appear to be suboptimal. As this could increase pertussis risk, greater awareness of the importance of timely vaccination completion is needed. GSK study identifier: HO-14-14383.

Impact of publicly available vaccination rates on parental school and child care choice

OBJECTIVE

Several states require schools and child cares to report vaccination rates, yet little is known about the impact of these policies. Our objectives were to assess: (1) predicted impact of vaccination rates on school/child care choice, (2) differences between vaccine hesitant and non-hesitant parents, and (3) differences by child's age.

METHODS

In 2016, a cross-sectional email survey of Colorado mothers with children ≤12 years old assessed value of vaccination rates in the context of school/child care choice. A willingness-to-pay framework measured preference for schools/child cares with different vaccination rates using tradeoff with commute time.

RESULTS

Response rate was 42% (679/1630). Twelve percent of respondents were vaccine hesitant. On a scale where 1 is "not important at all" and 4 is "very important" parents rated the importance of vaccination rates at 3.08. Respondents (including vaccine-hesitant respondents) would accept longer commutes to avoid schools/child cares with lower vaccination rates. Parents of child-care-age children were more likely to consider vaccination rates important.

CONCLUSIONS

This study shows parents highly value vaccination rates in the context of school and child care choice. Both hesitant and non-hesitant parents are willing to accept longer commute times to protect their children from vaccine-preventable diseases.

Impact of Childhood Vaccine Discussion Format Over Time on Immunization Status

OBJECTIVE

Presumptive formats to initiate childhood vaccine discussions (eg, "Well, we have to do some shots") have been associated with increased vaccine acceptance after one visit compared to participatory formats (eg, "How do you feel about vaccines?"). We characterize discussion format patterns over time and the impact of their repeated use on vaccine acceptance.

METHODS

We conducted a longitudinal prospective cohort study of children of vaccine-hesitant parents enrolled in a Seattle-based integrated health system. After the child's 2-, 4-, and 6-month visits, parents reported the format their child's provider used to begin the vaccine discussion (presumptive, participatory, or other). Our outcome was the percentage of days underimmunized of the child at 8 months old for 6 recommended vaccines. We used linear regression and generalized estimating equations to test the association of discussion format and immunization status.

RESULTS

We enrolled 73 parent-child dyads and obtained data from 82%, 73%, and 53% after the 2-, 4-, and 6-month visits, respectively. Overall, 65% of parents received presumptive formats at ≥1 visit and 42% received participatory formats at ≥1 visit. Parental receipt of presumptive formats at 1 and ≥2 visits (vs no receipt) was associated with significantly less underimmunization of the child, while receipt of participatory formats at ≥2 visits was associated with significantly more underimmunization. Visit-specific use of participatory (vs presumptive) formats was associated with a child being 10.1% (95% confidence interval, 0.3, 19.8; P = .04) more days underimmunized (amounting to, on average, 98 more days underimmunized for all 6 vaccines combined).

CONCLUSIONS

Presumptive (vs participatory) discussion formats are associated with increased immunization.

Factors Associated With Pediatrician Responses to Alternative Immunization Schedule Requests

We conducted a cross-sectional online survey among 4 chapters of the American Academy of Pediatrics from July through October 2014 to describe characteristics of pediatricians and practices associated with practice-level responses to alternative immunization schedule requests. Among 374 pediatricians, 58% reported frequent alternative immunization schedule requests and 24% reported feeling comfortable using them. Pediatricians who work in practices that accommodate alternative immunization schedule requests have increased odds of having a high frequency of alternative immunization schedule requests, and beliefs that relationships with families would be negatively affected if they refused requests. Practices that discontinue care to families who request alternative immunization schedules have increased odds of being a private group practice and having a formal office vaccine policy. Pediatricians are frequently asked to use alternative immunization schedules and many are not comfortable using them. Practice-level responses to alternative immunization schedules are associated with characteristics of pediatricians and practices.

Analytical Methods for a Learning Health System: 2. Design of Observational Studies

The second paper in a series on how learning health systems can use routinely collected electronic health data (EHD) to advance knowledge and support continuous learning, this review summarizes study design approaches, including choosing appropriate data sources, and methods for design and analysis of natural and quasi-experiments. The primary strength of study design approaches described in this section is that they study the impact of a deliberate intervention in real-world settings, which is critical for external validity. These evaluation designs address estimating the counterfactual - what would have happened if the intervention had not been implemented. At the individual level, epidemiologic designs focus on identifying situations in which bias is minimized. Natural and quasi-experiments focus on situations where the change in assignment breaks the usual links that could lead to confounding, reverse causation, and so forth. And because these observational studies typically use data gathered for patient management or administrative purposes, the possibility of observation bias is minimized. The disadvantages are that one cannot necessarily attribute the effect to the intervention (as opposed to other things that might have changed), and the results do not indicate what about the intervention made a difference. Because they cannot rely on randomization to establish causality, program evaluation methods demand a more careful consideration of the "theory" of the intervention and how it is expected to play out. A logic model describing this theory can help to design appropriate comparisons, account for all influential variables in a model, and help to ensure that evaluation studies focus on the critical intermediate and long-term outcomes as well as possible confounders.

Estimating Pertussis Susceptibility Among 0-23-Month-Old Children in the United States: Using National Immunization Survey (NIS) 2013

BACKGROUND

Despite high pertussis-containing vaccine coverage in the United States, children who are unvaccinated or not fully vaccinated remain susceptible to pertussis. Over multiple birth cohorts of incomplete vaccination, the number of children not immune to pertussis will accumulate because of factors such as age-specific vaccination status and dose-specific vaccine effectiveness. The total number of pertussis-susceptible children 0-23 months of age in the United States is unknown.

METHODS

Using data on age-specific pertussis-containing vaccine receipt among children evaluated in the 2013 National Immunization Survey (born between February 2011 and June 2012) and accounting for vaccine effectiveness and maternal transfer of antipertussis antibodies, we estimated the cumulative number of pertussis-susceptible children 0-23 months of age.

RESULTS

Of an estimated 7,905,672 children 0-23 months of age in the United States, we estimated that approximately 22% (1,716,429) are susceptible to pertussis. Age was a large factor in susceptibility, with 89% of children less than 2 months of age not immune to pertussis compared with 7% of children 21-23 months of age. In sensitivity analysis, increasing maternal pertussis vaccination coverage from 10% to 42% decreased susceptibility in children less than 2 months of age to 68%. When considering waning immunity after the fourth dose of vaccine, the herd protection threshold was no longer reached.

CONCLUSIONS

These estimates underscore the need to monitor age-specific pertussis vaccine coverage, to increase childhood and maternal pertussis vaccine coverage, to maintain population-level immunity and to prevent the spread of pertussis among young children.

Dutch national immunization schedule: compliance and associated characteristics for the primary series

In the Netherlands, the recommended priming immunization schedule for diphtheria, tetanus, pertussis and polio (DTaP-IPV) is at 2, 3 and 4 months of age. We evaluated the compliance with the recommended schedule, as well as its characteristics. We included all infants born between 2007 and 2012 who received minimally one DTaP-IPV vaccination (n = 1,061,578). Infants complied with the schedule if they received the first vaccination between 6 and 9 weeks of age, and the second and third vaccination 2-6 weeks after the first and second vaccination. We examined associations between compliance and several characteristics using log-binomial regression. Compliance for the first, second and third vaccination was 81.6, 88.3 and 84.2%, respectively. Compliance with the total recommended schedule was 64.5%, and increased from 60.1% for 2007 to 68.5% for 2012. Compliance was higher for full-term infants (65.9%), infants with normal birth weight (66.0%) and when both parents were born in the Netherlands (66.8%).

CONCLUSION

Delayed vaccination during the primary vaccination schedule occurs in one sixth of the Dutch children. Efforts to improve compliance should be focused in particular on preterm infants, infants with low birth weight and infants whose parents are not born in the Netherlands. What is Known: • A delayed start of vaccination leads to a longer period at risk for infectious diseases, e.g. pertussis • Delayed vaccination is associated with several factors including prematurity, low birth weight, family size, birth order, low socioeconomic status and health status of the child What is New: • Compliance with the recommended priming immunization schedule for diphtheria, tetanus, pertussis and polio was 64.5%, and increased from 60.1% for 2007 to 68.5% for 2012 • If the first vaccination was delayed, there was a higher chance that the following vaccinations were administered 'out-of-schedule' as well, resulting in even a higher age at second and third vaccination.

Immunological considerations regarding parental concerns on pediatric immunizations

Despite the fundamental role of vaccines in the decline of infant mortality, parents may decide to decline vaccination for their own children. Many factors may influence this decision, such as the belief that the infant immune system is weakened by vaccines, and concerns have been raised about the number of vaccines and the early age at which they are administered. Studies focused on the infant immune system and its reaction to immunizations, summarized in this review, show that vaccines can overcome those suboptimal features of infant immune system that render them more at risk of infections and of their severe manifestations. In addition, many vaccines have been shown to improve heterologous innate and adaptive immunity resulting in lower mortality rates for fully vaccinated children. Thus, multiple vaccinations are necessary and not dangerous, as infants can respond to several antigens as well as when responding to single stimuli. Current immunization schedules have been developed and tested to avoid vaccine interference, improve benefits and reduce side effects compared to single administrations. The infant immune system is therefore capable, early after birth, of managing several antigenic challenges and exploits them to prompt its development.

Population-Based Pertussis Incidence and Risk Factors in Infants Less Than 6 Months in Nepal

BACKGROUND.

Pertussis is estimated to cause 2 percent of childhood deaths globally and is a growing public health problem in developed countries despite high vaccination coverage. Infants are at greatest risk of morbidity and mortality. Maternal vaccination during pregnancy may be effective to prevent pertussis in young infants, but population-based estimates of disease burden in infants are lacking, particularly in low-income countries. The objective of this study was to estimate the incidence of pertussis in infants less than 6 months of age in Sarlahi District, Nepal.

METHODS.

Nested within a population-based randomized controlled trial of influenza vaccination during pregnancy, infants were visited weekly from birth through 6 months to assess respiratory illness in the prior week. If any respiratory symptoms had occurred, a nasal swab was collected and tested with a multitarget pertussis polymerase chain reaction (PCR) assay. The prospective cohort study includes infants observed between May 2011 and August 2014.

RESULTS.

The incidence of PCR-confirmed Bordetella pertussis was 13.3 cases per 1000 infant-years (95% confidence interval, 7.7-21.3) in a cohort of 3483 infants with at least 1 day of follow-up.

CONCLUSIONS.

In a population-based active home surveillance for respiratory illness, a low risk for pertussis was estimated among infants in rural Nepal. Nepal's immunization program, which includes a childhood whole cell pertussis vaccine, may be effective in controlling pertussis in infants.

Vaccine shot-limiting: Estimating the prevalence, indicators, and impact on vaccination status - Michigan, 2012

BACKGROUND

Concerns regarding vaccine safety and pain have prompted certain parents to limit the number of shots their child receives per visit. We estimated the prevalence of shot-limited children in Michigan, described their characteristics, assessed whether shot-limited children were up-to-date on recommended vaccinations, and investigated possible intervention points for vaccination education.

METHODS

We analyzed vaccination registry and birth record data of children born in Michigan during 2012 who had ⩾2 vaccination visits, with ⩾1 visits after age 5months. Shot-limited was defined as receiving ⩽2 shots at all visits through age 24months. Nonlimited children received >2 shots at ⩾1 visits. Up-to-date vaccination was based on receipt of a seven-vaccine series and was determined at ages 24months and 35months. Risk ratios (RR) were calculated using risk regression.

RESULTS

Of 101,443 children, a total of 2,967 (3%) children were shot-limited. Mothers of shot-limited children were more likely to be white (RR: 1.2; 95% confidence interval [CI]: 1.2-1.2), college graduate (RR: 1.9; 95% CI: 1.9-2.0), and married (RR: 1.5; 95% CI: 1.5-1.5). Compared with nonlimited children, shot-limited children were more likely to be born in a nonhospital setting (RR: 11.7; 95% CI: 9.4-14.6) and have a midwife attendant (RR: 1.9; 95% CI: 1.7-2.1). Shot-limited children were less likely to be up-to-date on recommended vaccinations (RR: 0.2; 95% CI: 0.2-0.3); this association was stronger for those with a midwife birth attendant (RR: 0.1; 95% CI: 0.1-0.2) rather than a medical doctor (RR: 0.3; 95% CI: 0.2-0.3).

CONCLUSIONS

Shot-limited children are less likely to be up-to-date on vaccinations, possibly leading to increased risk for vaccine-preventable diseases. This association was stronger for those with a midwife birth attendant. This analysis should prompt targeted education, such as to midwives, concerning risks associated with shot-limiting behavior.

Vaccination coverage and factors associated with adherence to the vaccination schedule in young children of a rural area in Burkina Faso

BACKGROUND

Vaccination is an important tool for reducing infectious disease morbidity and mortality. In the past, less than 80% of children 12-23 months of age were fully immunized in Burkina Faso.

OBJECTIVES

To describe coverage and assess factors associated with adherence to the vaccination schedule in rural area Burkina Faso.

METHODS

The study population was extracted from the Nouna Health and Demographic surveillance system cohort. Data from four rounds of interviews conducted between November 2012 and June 2014 were considered. This study included 4016 children aged 12-23 months. We assessed the effects of several background factors, including sex, factors reflecting access to health care (residence, place of birth), and maternal factors (age, education, marital status), on being fully immunized defined as having received Bacillus Calmette-Guérin (BCG), three doses of diphtheria-tetanus-pertussis and oral polio vaccine, and measles vaccine by 12 months of age. The associations were studied using binomial regression to derive prevalence ratios (PRs) in univariate and multivariate regression models.

RESULTS

The full vaccination coverage increased significantly over time (72% in 2012, 79% in 2013, and 81% in 2014, p = 0.003), and the coverage was significantly lower in urban than in rural areas (PR 0.84; 0.80-0.89). Vaccination coverage was neither influenced by sex nor influenced by place of birth or by maternal factors.

CONCLUSION

The study documented a further improvement in full vaccination coverage in Burkina Faso in recent years and better vaccination coverage in rural than in urban areas. The organization of healthcare systems with systematic outreach activities in the rural areas may explain the difference between rural and urban areas.

Undervaccination with diphtheria, tetanus, and pertussis vaccine: National trends and association with pertussis risk in young children

BACKGROUND

The high coverage for ≥3 pertussis vaccine doses among Taiwanese children might not imply timely vaccination. Recently, resurgence of pertussis and challenges with availability of DTaP-IPV-Hib prompted this study.

METHODS

In the 1996-2012 national birth cohort, we calculated the prevalence and days of undervaccination against pertussis by age 36 months. We also compared the odds of undervaccination in each laboratory-confirmed pertussis patient at ages 3-35 months with sex-, residence-, and age-matched controls from the general population, using conditional logistic regression.

RESULTS

The prevalence of undervaccination was 60.6% (median 16 days) and decreasing (p < 0.0001). Among 145 cases and 2,900 controls, 58 (40.0%) and 721 (24.9%) were undervaccinated (OR 2.28, 95% CI 1.57-3.31). The attributable risk percent was 22.5% (95% CI 14.5-27.9).

CONCLUSIONS

Undervaccination was decreasing. Approximately up to one-fifth pertussis cases in children aged 3-35 months could have been prevented with on-time vaccination.

Screening Tool Predicts Future Underimmunization Among a Pediatric Practice in Tennessee

The Parent Attitudes about Childhood Vaccines (PACV) survey for identifying vaccine-hesitant parents was recently validated in Washington State but did not include all recommended childhood vaccines. The current study compares vaccination rates for all recommended childhood vaccines and PACV scores at one pediatric practice in Tennessee. Children were enrolled at the 2-week well visit, and vaccination rates were assessed at 19 months of age. Outcomes at 19 months of age included mean percentage of days underimmunized and up-to-date status (yes/no) compared with PACV scores. The impact of provider on immunization status was assessed. Complete vaccination data were available for 158 children of 183 enrolled (86%). Higher PACV scores were associated with more days underimmunized (P < .001) and being overdue for vaccine doses at 19 months of age (P < .001). No difference was seen between providers and up-to-date status. Our study supports the predictive validity of the PACV for underimmunization.

Epidemiology of pertussis-related paediatric intensive care unit (ICU) admissions in Australia, 1997-2013: an observational study

OBJECTIVE

To review the epidemiology of pertussis-related intensive care unit (ICU) admissions across Australia, over a 17-year period.

DESIGN

Retrospective descriptive study.

SETTING

Australian ICUs contributing data to the Australian and New Zealand Paediatric Intensive Care (ANZPIC) Registry. The number of contributing ICUs increased over the study period, from 8 specialist paediatric ICUs in 1997 to 8 specialist paediatric and 13 general ICUs in 2013.

PARTICIPANTS

All paediatric (<16 years) ICU admissions, coded as pertussis-related, between 1 January 1997 and 31 December 2013.

RESULTS

A total of 373 pertussis-coded ICU admissions were identified in the ANZPIC Registry over the study period. Of these cases, 52.8% occurred during the 4 years of the recent Australian epidemic (2009-2012). ICU admissions were most likely to occur in infants aged younger than 6 weeks (41.8%, n=156) and aged 6 weeks to 4 months (42.9%, n=160). The median length of stay for pertussis-related ICU admissions was 3.6 days, with 77.5% of cases staying in ICU for <7 days. Approximately half of all admissions (54.8%) required some form of respiratory support, with 32.7% requiring invasive respiratory support. Over the study period, 23 deaths were recorded (6.2% of pertussis-related ICU admissions), of which 20 (87.0%) were infants <4 months old.

CONCLUSIONS

Pertussis-related ICU admissions occur primarily in infants too young to be fully protected from active immunisation. More needs to be done to protect these high-risk infants, such as maternal immunisation.

Association Between Vaccine Refusal and Vaccine-Preventable Diseases in the United States: A Review of Measles and Pertussis

IMPORTANCE

Parents hesitant to vaccinate their children may delay routine immunizations or seek exemptions from state vaccine mandates. Recent outbreaks of vaccine-preventable diseases in the United States have drawn attention to this phenomenon. Improved understanding of the association between vaccine refusal and the epidemiology of these diseases is needed.

OBJECTIVE

To review the published literature to evaluate the association between vaccine delay, refusal, or exemption and the epidemiology of measles and pertussis, 2 vaccine-preventable diseases with recent US outbreaks.

EVIDENCE REVIEW

Search of PubMed through November 30, 2015, for reports of US measles outbreaks that have occurred since measles was declared eliminated in the United States (after January 1, 2000), endemic and epidemic pertussis since the lowest point in US pertussis incidence (after January 1, 1977), and for studies that assessed disease risk in the context of vaccine delay or exemption.

FINDINGS

We identified 18 published measles studies (9 annual summaries and 9 outbreak reports), which described 1416 measles cases (individual age range, 2 weeks-84 years; 178 cases younger than 12 months) and more than half (56.8%) had no history of measles vaccination. Of the 970 measles cases with detailed vaccination data, 574 cases were unvaccinated despite being vaccine eligible and 405 (70.6%) of these had nonmedical exemptions (eg, exemptions for religious or philosophical reasons, as opposed to medical contraindications; 41.8% of total). Among 32 reports of pertussis outbreaks, which included 10,609 individuals for whom vaccination status was reported (age range, 10 days-87 years), the 5 largest statewide epidemics had substantial proportions (range, 24%-45%) of unvaccinated or undervaccinated individuals. However, several pertussis outbreaks also occurred in highly vaccinated populations, indicating waning immunity. Nine reports (describing 12 outbreaks) provided detailed vaccination data on unimmunized cases; among 8 of these outbreaks from 59% through 93% of unvaccinated individuals were intentionally unvaccinated.

CONCLUSIONS AND RELEVANCE

A substantial proportion of the US measles cases in the era after elimination were intentionally unvaccinated. The phenomenon of vaccine refusal was associated with an increased risk for measles among people who refuse vaccines and among fully vaccinated individuals. Although pertussis resurgence has been attributed to waning immunity and other factors, vaccine refusal was still associated with an increased risk for pertussis in some populations.

Infant vaccination timing: Beyond traditional coverage metrics for maximizing impact of vaccine programs, an example from southern Nepal

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We prospectively examined, via weekly recall, the timing of EPI immunizations in infants less than 6 months in rural Nepal.

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The majority of infants less than 6 months received immunizations on a delayed schedule.

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National immunization coverage estimates do not capture delay in the first 6 months of life.

Background

Immunization programs currently measure coverage by assessing the proportion of children 12–24 months who have been immunized but this does not address the important question of when the scheduled vaccines were administered. Data capturing the timing of vaccination in first 6 months, when severe disease is most likely to occur, are limited.

Objective

To estimate the time to Bacillus Calmette–Guérin (BCG) (recommended at birth), diphtheria-tetanus-pertussis-H, influenza b-hepatitis B (DTP-Hib-HepB), and oral polio vaccine (OPV) (recommended at 6, 10, and 14 weeks) vaccinations and risk factors for vaccination delay in infants <6 months of age in a district in southern Nepal where traditional coverage metrics are high.

Design/methods

Infants enrolled in a randomized controlled trial of maternal influenza vaccination were visited weekly at home from birth through age 6 months to ascertain if any vaccinations had been given in the prior week. Infant, maternal, and household characteristics were recorded. BCG, DTP-Hib-HepB, and OPV vaccination coverage at 4 and 6 months was estimated. Time to vaccination was estimated through Kaplan–Meier curves; Cox-proportional hazards models were used to examine risk factors for delay for the first vaccine.

Results

The median age of BCG, first OPV and DTP-Hib-HepB receipt was 22, 21, and 18 weeks, respectively. Almost half of infants received no BCG by age 6 months. Only 8% and 7% of infants had received three doses of OPV and DTP-Hib-HepB, respectively, by age 6 months.

Conclusion

A significant delay in receipt of infant vaccines was found in a prospective, population-based, cohort in southern Nepal despite traditional coverage metrics being high. Immunization programs should consider measuring time to receipt relative to the official schedule in order to maximize benefits for disease control and child health.

Vaccine Hesitancy: Causes, Consequences, and a Call to Action

Vaccine hesitancy reflects concerns about the decision to vaccinate oneself or one's children. There is a broad range of factors contributing to vaccine hesitancy, including the compulsory nature of vaccines, their coincidental temporal relationships to adverse health outcomes, unfamiliarity with vaccine-preventable diseases, and lack of trust in corporations and public health agencies. Although vaccination is a norm in the U.S. and the majority of parents vaccinate their children, many do so amid concerns. The proportion of parents claiming non-medical exemptions to school immunization requirements has been increasing over the past decade. Vaccine refusal has been associated with outbreaks of invasive Haemophilus influenzae type b disease, varicella, pneumococcal disease, measles, and pertussis, resulting in the unnecessary suffering of young children and waste of limited public health resources. Vaccine hesitancy is an extremely important issue that needs to be addressed because effective control of vaccine-preventable diseases generally requires indefinite maintenance of extremely high rates of timely vaccination. The multifactorial and complex causes of vaccine hesitancy require a broad range of approaches on the individual, provider, health system, and national levels. These include standardized measurement tools to quantify and locate clustering of vaccine hesitancy and better understand issues of trust; rapid, independent, and transparent review of an enhanced and appropriately funded vaccine safety system; adequate reimbursement for vaccine risk communication in doctors' offices; and individually tailored messages for parents who have vaccine concerns, especially first-time pregnant women. The potential of vaccines to prevent illness and save lives has never been greater. Yet, that potential is directly dependent on parental acceptance of vaccines, which requires confidence in vaccines, healthcare providers who recommend and administer vaccines, and the systems to make sure vaccines are safe.

Characteristics of Physicians Who Dismiss Families for Refusing Vaccines

BACKGROUND AND OBJECTIVES

Physicians dismissing families who refuse vaccines from their practices is controversial. We assessed the following among pediatricians (Peds) and family physicians (FPs): (1) reported prevalence of parental refusal of 1 or more vaccines in the infant series; (2) physician response to refusal; and (3) the association between often/always dismissing families and provider/practice characteristics and state exemption laws.

METHODS

Nationally representative survey conducted June to October 2012. A multivariable analysis assessed association of often/always dismissing families with physician/practice characteristics, state philosophical exemption policy, and degree of difficulty obtaining nonmedical exemptions.

RESULTS

The response rate was 66% (534/815). Overall, 83% of physicians reported that in a typical month, ≥1% of parents refused 1 or more infant vaccines, and 20% reported that >5% of parents refused. Fifty-one percent reported always/often requiring parents to sign a form if they refused (Peds 64%, FP 29%, P < .0001); 21% of Peds and 4% of FPs reported always/often dismissing families if they refused ≥1 vaccine. Peds only were further analyzed because few FPs dismissed families. Peds who dismissed families were more likely to be in private practice (adjusted odds ratio [aOR] 4.90, 95% confidence interval [CI] 1.40-17.19), from the South (aOR 4.07, 95% CI 1.08-15.31), and reside in a state without a philosophical exemption law (aOR 3.70, 95% CI 1.74-7.85).

CONCLUSIONS

Almost all physicians encounter parents who refuse infant vaccines. One-fifth of Peds report dismissing families who refuse, but there is substantial variation in this practice. Given the frequency of dismissal, the impact of this practice on vaccine refusers and on pediatric practices should be studied.