Persistence of antibodies 3 years after booster vaccination of adults with combined acellular pertussis, diphtheria and tetanus toxoids vaccine

Waning rate of immunity and duration of protective immunity against diphtheria toxoid as a function of age and number of doses: Systematic review and quantitative data analysis

Although the burden of diphtheria has declined greatly since the introduction of vaccines, sporadic outbreaks continue to be reported. WHO recommends booster doses after a primary series, but questions remain about the optimal interval between these doses. We conducted a systematic review and quantitative data analysis to quantify the duration of protective immunity after different numbers of doses. Fifteen cross-sectional seroprevalence studies provided data on geometric mean concentration (GMC). Single-year age-stratified GMCs were analyzed using a mixed-effect linear regression model with a random intercept incorporating the between-country variability. GMC was estimated to decline to 0.1 IU/ml in 2.5 years (95% CI: 0.9-4.0), 10.3 years (95% CI: 7.1-13.6), and 25.1 years (95% CI: 7.6-42.6) after receiving three, four and five doses, respectively. The results drawn from cross-sectional data collected in countries with different epidemiologies, vaccines, and schedules had several limitations. However, these analyses contribute to the discussion of optimal timing between booster doses of diphtheria toxoid-containing vaccine.

Pertussis immunisation during pregnancy: Antibody levels and the impact of booster vaccine

Pertussis (whooping cough) is a highly infectious disease caused by Bordetella pertussis. Mothers lacking adequate immunity and contracting the disease represent the biggest risk of transmission to new-borns, for which the disease is often a threat. The aim of the study was to estimate the frequency of pertussis susceptibility among pregnant women, in order to point out the need for a vaccine recall during pregnancy, and to evaluate the antibody response in already vaccinated women. A cross-sectional observational study was conducted in the blood test centre of "St. Anna" Obstetrics and Gynaecology Hospital in Turin (Piedmont, Italy). Eligibility criteria included pregnant women coming to the centre for any blood test, aged 18 or above and with gestational age between 33 and 37 weeks at the moment of the blood draw. The data collection was carried out from May 2019 to January 2020 and the concentration of anti-Pertussis Toxin (anti-PT) IgG was measured through the Enzyme-Linked Immunosorbent Assay (ELISA) technique. Two-hundred women (median age 35) were enrolled: 132 (66%) had received at least one dose of pertussis vaccine, 82 of which during pregnancy. Recently vaccinated women had significantly higher antibody titres (even 12-15 times as high) compared to those vaccinated more than 5 years before or never vaccinated at all (p < 0.0001). Moreover, 95.1% of recently vaccinated women had anti-PT IgG levels above 10 IU/ml, and 85.4% above 20 IU/ml, while the same proportions were as low as 37% and 21% (respectively) in the group of women not vaccinated in pregnancy. This study confirmed that the vaccination is greatly effective in ensuring high antibody titres in the first months after the booster vaccine, with considerable differences in anti-PT IgG compared to women vaccinated earlier or never vaccinated at all, and therefore vaccinating pregnant women against pertussis still represents a valuable strategy.

An observational study of antibody responses to a primary or subsequent pertussis booster vaccination in Australian healthcare workers

Adult pertussis vaccination is increasingly recommended to control pertussis in the community. However, there is little data on the duration and kinetics of immunity to pertussis boosters in adults. We compared IgG responses to vaccination with a tetanus, low-dose diphtheria, low-dose acellular pertussis (Tdap) booster at 1 week, 1 month and 1 year post-vaccination in whole-cell (wP)-primed Australian paediatric healthcare workers who had received an adult Tdap booster 5-12 years previously, to those who received their first Tdap booster. Tdap vaccination was well tolerated in both groups. Previously boosted adults had significantly higher pre-vaccination IgG concentrations for all vaccine-antigens, and more were seropositive for pertussis toxin (PT)-specific IgG (≥ 5 IU/mL) (69.5%; 95% confidence interval (CI) 59.5-79.5) than adults in the naïve group (45.2%; 95% CI 32.8-57.5). Tdap vaccination significantly increased IgG responses 1 month post-vaccination in both groups. This increase was more rapid in previously boosted than in naïve adults, with geometric mean fold-increases in PT-IgG at 1 week post vaccination of 3.6 (95% CI 2.9-4.3) and 2.6 (95% CI 2.2-3.2), respectively. Antibody waning between 1 month and 1 year post-vaccination was similar between groups for IgG specific to PT and filamentous haemagglutinin (FHA), but was faster for IgG against pertactin (PRN) in the naïve group (GMC ratio 0.36; 95% CI 0.31-0.42) than the previously boosted group (GMC ratio 0.45; 95% CI 0.39-0.50). At baseline, all but one adult had protective IgG titres against tetanus toxin (TT) (≥ 0.1 IU/mL), and 75.6% in the previously boosted and 61.3% in the naïve group had protective IgG titres against diphtheria toxoid (DT) of ≥ 0.1 IU/mL. This study shows that pertussis immune memory is maintained up to 12 years after Tdap vaccination in wP-primed Australian adults. There was no evidence that pertussis immune responses waned faster after a booster dose. These findings support current recommendations of repeating Tdap booster vaccination in paediatric healthcare workers at least every 10 years. Clinical trials registry: ACTRN12615001262594.

Use of Tetanus Toxoid, Reduced Diphtheria Toxoid, and Acellular Pertussis Vaccines: Updated Recommendations of the Advisory Committee on Immunization Practices - United States, 2019

Since 2005, a single dose of tetanus toxoid, reduced diphtheria toxoid, and acellular pertussis (Tdap) vaccine has been recommended by the Advisory Committee on Immunization Practices (ACIP) for adolescents and adults (1,2). After receipt of Tdap, booster doses of tetanus and diphtheria toxoids (Td) vaccine are recommended every 10 years or when indicated for wound management. During the October 2019 meeting of ACIP, the organization updated its recommendations to allow use of either Td or Tdap where previously only Td was recommended. These situations include decennial Td booster doses, tetanus prophylaxis when indicated for wound management in persons who had previously received Tdap, and for multiple doses in the catch-up immunization schedule for persons aged ≥7 years with incomplete or unknown vaccination history. Allowing either Tdap or Td to be used in situations where Td only was previously recommended increases provider point-of-care flexibility. This report updates ACIP recommendations and guidance regarding the use of Tdap vaccines (3).

Maternal tetanus, diphtheria, and acellular pertussis (Tdap) and influenza immunization: an overview

BACKGROUND

Maternal tetanus, diphtheria, and acellular pertussis (Tdap) and influenza immunization for women during pregnancy (the so-called "maternal immunization") has been introduced in several countries, and recently also in Italy, to protect mother and fetus during pregnancy, infant in his first months of life and mother during postpartum period. However, very low vaccination coverage rates have been reached due to several variables.

METHODS

A literature search was conducted on PubMed and Embase, including any experimental or observational studies, to assesses existing evidence on the effectiveness, efficacy, safety and optimal timing of administration of Tdap and influenza immunization in pregnancy for mothers and their infants. The search was finalized in August 2019.

RESULTS

Reviewing the literature, we identified only a few studies that, among several maternal and infant outcomes, found sporadic significant associations with maternal influenza immunization and even less with Tdap immunization. Moreover, most of the authors of these studies explained these findings as a result of residual confounding effect. The effectiveness of maternal influenza immunization is more complicated to prove than the effectiveness of Tdap immunization because of several reasons. Not all nations recommend and offer vaccines in the same weeks of pregnancy and this one manifests the complexity in defining the best timing for Tdap or influenza immunization.

CONCLUSIONS

The safety of maternal Tdap or influenza immunization is supported by the evidence so far, however, regular surveillance should be maintained, especially with regard to the influenza vaccine that changes in formulation each year. There is a need to optimize the timing of vaccination in pregnancy and to have a national system of detection of maternal immunization in each country.

Assessment of IgA anti-PT and IgG anti-ACT reflex testing to improve Bordetella pertussis serodiagnosis in recently vaccinated subjects

OBJECTIVES

Quantifying IgG antibodies to pertussis toxin (PT) is the most specific and sensitive method for the serodiagnosis of a Bordetella pertussis infection. Since PT is a component of acellular pertussis vaccines, anti-PT IgG is also induced by vaccination, precluding pertussis serodiagnosis based exclusively on anti-PT IgG in recently vaccinated subjects. Here, we aim to identify additional B. pertussis-specific serological markers that can discriminate between infection and recent vaccination.

METHODS

The clinical usefulness of measuring IgA directed to the vaccine antigen PT and IgG directed to non-vaccine antigens (Fim2/3, LPS, ACT, CatACT) was evaluated in nine well characterized subject groups, aged 10-89 years (n = 390). Serum anti-PT IgG levels (>125 IU/mL) served as an indicator for a recent B. pertussis infection. Comparing symptomatic pertussis-infected subjects (n = 140) with recently vaccinated, non-infected subjects (n = 100) revealed the optimal cut-off, accuracy, sensitivity and specificity for each single parameter.

RESULTS

For pertussis diagnosis in recently vaccinated subjects, the measurement of anti-PT IgA (cut-off 15 IU/mL) and anti-ACT IgG (cut-off 15 U/mL) resulted in accuracies of 95% (91.5-97.1) and 87.5% (82.7-91.1), sensitivities of 92.9% (87.4-96.0) and 83.6% (76.5-88.8) and specificities of 98% (93.0-99.4) and 93% (86.3-96.6), respectively. Comparing anti-PT IgA levels between the youngest (10-19 years, n = 38) and oldest (70-89 years, n = 17) age groups revealed an age-dependent increase in antibody levels in pertussis-infected subjects (p < 0.0001).

CONCLUSIONS

Reflex testing of anti-PT IgA and anti-ACT IgG improves pertussis serodiagnosis in recently vaccinated symptomatic subjects with elevated anti-PT IgG levels. Furthermore, both markers can discriminate between vaccination and recent infection in pertussis serosurveillance studies.

The burden of pertussis in older adults: what is the role of vaccination? A systematic literature review

INTRODUCTION

Pertussis (whooping cough) is a vaccine-preventable disease; however, neither natural- nor vaccine-induced protection is life-long. Although generally not severe in adults, pertussis can be associated with complications in patients with chronic conditions such as asthma or chronic obstructive pulmonary disease, and can be readily transmitted to more vulnerable populations, including neonates before they complete their primary vaccination. Furthermore, as the global population ages, the health and economic burden of the disease is expected to rise. Areas covered: A systematic literature review was conducted to ascertain the current epidemiological and financial burden of pertussis in older adults and to discuss the potential value of a booster vaccination in this population. Expert commentary: Our review indicates a considerable underestimation of the pertussis burden amongst older adults. Seroprevalence studies consistently demonstrate that the reported incidence may be much lower than the actual incidence. Tetanus toxoid-reduced diphtheria toxoid and acellular pertussis vaccines are immunogenic in older adults, induce high booster responses and are well-tolerated. There is therefore a good rationale for the advocacy of booster pertussis vaccination throughout life to prevent pertussis infection and its transmission, especially in adults aged ≥50 years.

Trends in Tdap vaccination among privately insured pregnant women in the United States, 2009-2016

BACKGROUND

Infants younger than 6 months are at increased risk of complications and mortality from pertussis infection. In October 2012, the Advisory Committee on Immunization Practices revised its recommendation to include a Tdap dose during each pregnancy, ideally between 27 and 36 weeks gestation.

OBJECTIVE

Assess trends in Tdap vaccination coverage among privately insured pregnant women from 2009 to 2016 including timing of Tdap vaccination (before, during, or after pregnancy), trimester of vaccination for women vaccinated during pregnancy, and missed vaccination opportunities for unvaccinated women. Identify factors associated with vaccination during the optimal period of 27-36 weeks gestation.

STUDY DESIGN

Retrospective analysis of privately insured women 15-49 years who delivered live births during 2009-2016 conducted using 2009-2016 MarketScan data. Tdap vaccination coverage and the timing of Tdap vaccine administration were assessed for women continuously enrolled from 6 months before pregnancy to 1 month after delivery. Multivariable logistic regression was performed to identify factors independently associated with receipt of Tdap vaccine at 27-36 weeks gestation.

RESULTS

Tdap vaccination coverage during pregnancy increased from 0.4% in 2009 to 6.2% in 2012 and to 53.2% in 2016. The proportion of vaccinated women receiving Tdap at 27-36 weeks gestation increased from <10% in 2009 to nearly 90% in 2016, with most vaccination occurring at 27-32 weeks gestation. Women of older age, residing in a metropolitan statistical area, residing outside the South, and having a capitated health insurance plan were more likely to receive Tdap at 27-36 weeks gestation than their counterparts. Among women not vaccinated during pregnancy, 77.7% had a pregnancy-related medical claim between 27 and 36 weeks gestation.

CONCLUSION

Tdap vaccination coverage during pregnancy increased significantly from 2009 to 2016, with the greatest increase occurring after the revised Advisory Committee on Immunization Practices recommendation. Most women who did not receive Tdap vaccine had a missed vaccination opportunity during pregnancy, indicating potential for much higher vaccination coverage and consequent infant protection against pertussis.

Antibody persistence and safety and immunogenicity of a second booster dose nine years after a first booster vaccination with a reduced antigen diphtheria-tetanus-acellular pertussis vaccine (Tdap) in adults

BACKGROUND

Over the last decades, pertussis showed periodic increases in its incidence among adults, despite being a vaccine-preventable disease.

METHODS

This phase III, multicenter, extension study (NCT00489970) was conducted in adults from the United States, followed at Year (Y) 5 and Y9 post-vaccination with a dose of reduced-antigen-content tetanus-diphtheria-acellular pertussis vaccine containing either 3 (Tdap-B group) or 5 pertussis components (Tdap-A group). Willing participants in Tdap groups and newly-recruited participants (Control group) received one Tdap-B dose at Y9. Antibody persistence (at Y5 and Y9) and safety of Tdap-B at Y9 were assessed. Non-inferiority of immune response elicited by 2 Tdap doses was evaluated at Y9: (i) versus one Tdap-B dose for diphtheria and tetanus in terms of seroprotection rates; (ii) for all antigens in terms of booster response rates (Tdap-B and Tdap-A groups versus Control group); and (iii) for pertussis antigens in terms of geometric mean concentrations (GMCs) versus a 3-dose series of a combined diphtheria-tetanus-acellular pertussis vaccine (DTPa) administered during infancy.

RESULTS

1257 participants were enrolled at Y5 and 809 participants were vaccinated at Y9. Seroprotection rates in both Tdap groups were ≥98.4% and ≥98.0% (Y5) and ≥98.3% and ≥98.1% (Y9) for diphtheria and tetanus, respectively. For pertussis antigens, antibody concentrations above assay cut-offs were observed for ≥76.6% (Y5) and ≥84.9% (Y9) of participants in Tdap groups. At Y9, one month post-Tdap vaccination, comparable seroprotection/seropositivity rates and antibody GMCs were observed among groups. Non-inferiority of immune responses in both Tdap groups was demonstrated when compared to the Control group for diphtheria and tetanus and to a 3-dose DTPa series for pertussis antigens. Non-inferiority criteria in terms of booster response were not met for all antigens. No safety concerns were raised.

CONCLUSION

A second dose of Tdap-B administered in adults, 9 years after initial Tdap vaccination, is immunogenic and well-tolerated.

Prevention of pertussis: from clinical trials to Real World Evidence

Pertussis, a highly contagious infective disease caused by Bordetella pertussis, was in the past very common among newborns and children, causing significant medical, social and economic issues burden, also due to frequent need of hospitalization and high mortality. Following the introduction of vaccines against pertussis, the burden of the disease dramatically decreased, although nowadays, this disease it is still the most widespread among the vaccine preventable ones. First vaccine formulations were composed with whole cell antigen of Bordetella pertussis and were followed by formulations with acellular antigens (PT, FHA, PRN, FIM), that showed to have similar efficacy and less reactogenicity. In particular, all the acellular vaccines, regardless the number of antigenic component included, demonstrated good immunogenicity in clinical trials and high effectiveness in real world evidence studies. Nevertheless, in the recent years it has been notified an increasing number of cases of pertussis. The most recent evidence demonstrated that for an effective control and prevention of pertussis it is necessary to strengthen vaccination coverage among the whole population, providing primary vaccination to newborns and booster in infancy, adolescence and adulthood every 10 years. Finally, vaccination of women at the third trimester of every pregnancy is the most effective intervention to protect the newborn from pertussis in his first months of life, before developing a protective response after the primary vaccination.

Prevention of pertussis: An unresolved problem

Pertussis is a highly contagious respiratory disease caused by Bordetella pertussis. However, after the introduction of the whole-cell pertussis vaccine (wP), the annual incidence rates of the disease progressively declined. Despite this result, the inclusion of wP in the national immunization schedule of infants and young children was debated regarding its safety. Several efforts to produce vaccines based on B. pertussis components capable of evoking protective immunity with no or limited adverse events were made. Of these others, five pertussis antigens were considered possible components of acellular vaccines (aPs): pertussis toxin (PT), filamentous haemagglutinin (FHA), pertactin (PRN) and fimbria proteins 2 and 3. However, the introduction of aPs was followed by a slight but progressive increase in the incidence of pertussis. This paper discusses the potential reasons for reduced aPs efficacy. Moreover, it attempts to evaluate the real effectiveness of aPs and the potential differences between available preparations. Data analysis showed that several boosters are needed to maintain protection against pertussis and additional studies are needed to confirm the antigens that should be included in aPs to improve the prevention of pertussis.

Prevention of Pertussis, Tetanus, and Diphtheria with Vaccines in the United States: Recommendations of the Advisory Committee on Immunization Practices (ACIP)

This report compiles and summarizes all recommendations from CDC's Advisory Committee on Immunization Practices (ACIP) regarding prevention and control of tetanus, diphtheria, and pertussis in the United States. As a comprehensive summary of previously published recommendations, this report does not contain any new recommendations and replaces all previously published reports and policy notes; it is intended for use by clinicians and public health providers as a resource. ACIP recommends routine vaccination for tetanus, diphtheria, and pertussis. Infants and young children are recommended to receive a 5-dose series of diphtheria and tetanus toxoids and acellular pertussis (DTaP) vaccines, with one adolescent booster dose of tetanus toxoid, reduced diphtheria toxoid, and acellular pertussis (Tdap) vaccine. Adults who have never received Tdap also are recommended to receive a booster dose of Tdap. Women are recommended to receive a dose of Tdap during each pregnancy, which should be administered from 27 through 36 weeks’ gestation, regardless of previous receipt of Tdap. After receipt of Tdap, adolescents and adults are recommended to receive a booster tetanus and diphtheria toxoids (Td) vaccine every 10 years to assure ongoing protection against tetanus and diphtheria.

Randomized Controlled Trial of the Safety and Immunogenicity of Revaccination With Tetanus-Diphtheria-Acellular Pertussis Vaccine (Tdap) in Adults 10 Years After a Previous Dose

BACKGROUND

Reduced-antigen-content tetanus, diphtheria, and acellular pertussis (Tdap) vaccine is recommended in many countries for boosting immunity in adolescents and adults. Although immunity to these antigens wanes with time, currently available Tdap products are not labeled for repeat administration in the United States.

METHODS

We performed an observer-blinded, randomized controlled trial in 1330 adults aged 18 to <65 years who received either the Tdap (n = 1002) or tetanus-diphtheria (Td) (n = 328) vaccine 8 to 12 years after a dose of Tdap vaccine administered previously. Solicited adverse events following immunization were documented for 7 days after vaccination, and serious adverse events and adverse events of medical significance were documented for 6 months after vaccination. Levels of antibodies against component vaccine antigens were measured before and 1 month after vaccination.

RESULTS

A solicited adverse event was reported by 87.7% of Tdap and 88.0% of Td vaccine recipients. We found no significant differences in the rates of injection-site reactions, systemic reactions, or serious adverse events between the vaccine groups. A robust antibody response to each pertussis antigen in the Tdap-vaccinated group was found; postvaccination-to-prevaccination geometric mean antibody concentration ratios were 8:1 (pertussis toxoid), 5.9 (filamentous hemagglutinin), 6.4 (pertactin), and 5.2 (fimbriae 2 and 3). Postvaccination geometric mean concentrations of tetanus antibody (4.20 and 4.74 IU/mL, respectively) and diphtheria antibody (10.1 and 12.6 IU/mL, respectively) were similar in the Tdap and Td groups, and the rates of seroprotection against tetanus and diphtheria were >99% in both groups.

CONCLUSIONS

A second dose of Tdap vaccine in adults approximately 10 years after a previous dose was well tolerated and immunogenic. These data might facilitate consideration of providing Tdap booster doses to adults.

Antenatal vaccination to decrease pertussis in infants: safety, effectiveness, timing, and implementation

Pertussis remains a serious global health issue in infants aged less than 6 months. Neonates and young infants have the highest risk of developing pertussis as they are too young to be vaccinated and thus are more likely to develop more severe pertussis-related complications, including death. Protecting this vulnerable age population from pertussis is considered a main priority in many national health programs. Two vaccine strategies exist to protect infants from pertussis: "cocooning" and maternal vaccination during pregnancy. The latter is the more recent and preferred strategy, which protects newborns by passive transplacental transfer of pertussis antibodies. We review the reported evidence on the safety, effectiveness, timing and implementation of this antenatal immunization strategy.

A phase I, randomized, controlled, dose-ranging study of investigational acellular pertussis (aP) and reduced tetanus-diphtheria-acellular pertussis (TdaP) booster vaccines in adults

Despite high vaccination coverage worldwide, pertussis has re-emerged in many countries. This randomized, controlled, observer-blind phase I study and extension study in Belgium (March 2012-June 2015) assessed safety and immunogenicity of investigational acellular pertussis vaccines containing genetically detoxified pertussis toxin (PT) (NCT01529645; NCT02382913). 420 healthy adults (average age: 26.8 ± 5.5 years, 60% female) were randomized to 1 of 10 vaccine groups: 3 investigational aP vaccines (containing pertussis antigens PT, filamentous hemagglutinin [FHA] and pertactin [PRN] at different dosages), 6 investigational TdaP (additionally containing tetanus toxoid [TT] and diphtheria toxoid [DT]), and 1 TdaP comparator containing chemically inactivated PT. Antibody responses were evaluated on days 1, 8, 30, 180, 365, and approximately 3 years post-booster vaccination. Cell-mediated immune responses and PT neutralization were evaluated in a subset of participants in pre-selected groups. Local and systemic adverse events (AEs), and unsolicited AEs were collected through day 7 and 30, respectively; serious AEs and AEs leading to study withdrawal were collected through day 365 post-vaccination. Antibody responses against pertussis antigens peaked at day 30 post-vaccination and then declined but remained above baseline level at approximately 3 years post-vaccination. Responses to FHA and PRN were correlated to antigen dose. Antibody responses specific to PT, toxin neutralization activity and persistence induced by investigational formulations were similar or significantly higher than the licensed vaccine, despite lower PT doses. Of 15 serious AEs, none were considered vaccination-related; 1 led to study withdrawal (premature labor, day 364; aP4 group). This study confirmed the potential benefits of genetically detoxified PT antigen. All investigational study formulations were well tolerated.

Effect of Prepregnancy Pertussis Vaccination in Young Infants

Background

Maternal antibodies to pertussis can hamper infant immune responses to pertussis vaccines. The effect a maternal tetanus, diphtheria, acellular pertussis (Tdap) vaccine booster between 2 consecutive pregnancies is investigated.

Methods

A prospective study was conducted in Belgium during 2008-2014 on the kinetics of maternal pertussis antibodies in unvaccinated women and their infants (group A; 86 mother-infant pairs) and in siblings born after the women received Tdap vaccine (group B; 58 mother-infant pairs). Levels of antibody to pertussis toxin, antibody to filamentous hemagglutinin, and antibody to pertactin were measured in maternal blood before and after vaccination and at both deliveries, in cord blood from both siblings, and in infants before and after they received a priming series of acellular pertussis containing vaccines.

Results

Levels of pertussis antibodies in all group B siblings at birth were significantly higher than those in their siblings at birth, even as the interval since maternal vaccination increased. Blunting of the infant pertussis vaccine response was detected in group B siblings. We estimated the maximum interval between repeat Tdap vaccine doses in adult women that would yield a beneficial effect for the consecutive infant.

Conclusions

Prepregnancy Tdap vaccination significantly increases maternal antibody concentrations in consecutive infants. However, similar to the effect of Tdap vaccination during pregnancy, immune responses of later-born infants born to mothers who received a prepregnancy immunization, are blunted.

The relationship between mucosal immunity, nasopharyngeal carriage, asymptomatic transmission and the resurgence of Bordetella pertussis

The incidence of whooping cough in the US has been rising slowly since the 1970s, but the pace of this has accelerated sharply since acellular pertussis vaccines replaced the earlier whole cell vaccines in the late 1990s. A similar trend occurred in many other countries, including the UK, Canada, Australia, Ireland, and Spain, following the switch to acellular vaccines. The key question is why. Two leading theories (short duration of protective immunologic persistence and evolutionary shifts in the pathogen to evade the vaccine) explain some but not all of these shifts, suggesting that other factors may also be important.

In this synthesis, we argue that sterilizing mucosal immunity that blocks or abbreviates the duration of nasopharyngeal carriage of Bordetella pertussis and impedes person-to-person transmission (including between asymptomatically infected individuals) is a critical factor in this dynamic. Moreover, we argue that the ability to induce such mucosal immunity is fundamentally what distinguishes whole cell and acellular pertussis vaccines and may be pivotal to understanding much of the resurgence of this disease in many countries that adopted acellular vaccines. Additionally, we offer the hypothesis that observed herd effects generated by acellular vaccines may reflect a modification of disease presentation leading to reduced potential for transmission by those already infected, as opposed to inducing resistance to infection among those who have been exposed.

Brief Report: Seroprevalence of Pertussis Infection in HIV-Infected Adults in the United States

Pertussis is a resurgent infection that can cause significant morbidity among adults. CD4 T cells are necessary for its clearance, but pertussis studies in HIV-infected adults are limited to case reports. We analyzed stored serum samples from 299 HIV-infected adults to determine the seroprevalence of pertussis among this population. We found that 4.3% of subjects had serologic evidence of recent pertussis infection, and annual incidence of pertussis infection among subjects not vaccinated against pertussis in the last 5 years was 10.5%-17.5%. Prospective studies are needed to define the clinical presentation of pertussis in HIV-infected adults and to optimize vaccination strategies.

Tetanus-diphtheria-acellular pertussis vaccination for adults: an update

Although tetanus and diphtheria have become rare in developed countries, pertussis is still endemic in some developed countries. These are vaccine-preventable diseases and vaccination for adults is important to prevent the outbreak of disease. Strategies for tetanus, diphtheria, and pertussis vaccines vary from country to country. Each country needs to monitor consistently epidemiology of the diseases and changes vaccination policies accordingly. Recent studies showed that tetanus–diphtheria–acellular pertussis vaccine for adults is effective and safe to prevent pertussis disease in infants. However, vaccine coverage still remains low than expected and seroprevalence of protective antibodies levels for tetanus, diphtheria, and pertussis decline with aging. The importance of tetanus–diphtheria–acellular pertussis vaccine administration should be emphasized for the protection of young adult and elderly people also, not limited to children.

The Pertussis resurgence: putting together the pieces of the puzzle

Pertussis incidence is rising in almost every country where acellular pertussis (aP) vaccines have been introduced, and is occurring across all age groups from infancy to adulthood. The key question is why? While several known factors such as waning of immunity, detection bias due to more sensitive tests and higher awareness of the disease among practitioners, and evolutionary shifts among B. pertussis all likely contribute, collectively, these do not adequately explain the existing epidemiologic data, suggesting that additional factors also contribute. Key amongst these is recent data indicating that the immune responses induced by aP vaccines differ fundamentally from those induced by the whole cell pertussis (wP) vaccines, and do not lead to mucosal immunity. If so, it appears likely that differences in how the two categories of vaccines work, may be pivotal to our overall understanding of the pertussis resurgence.

Forecasting Epidemiological Consequences of Maternal Immunization

BACKGROUND

 The increase in the incidence of whooping cough (pertussis) in many countries with high vaccination coverage is alarming. Maternal pertussis immunization has been proposed as an effective means of protecting newborns during the interval between birth and the first routine dose. However, there are concerns regarding potential interference between maternal antibodies and the immune response elicited by the routine schedule, with possible long-term population-level effects.

METHODS

 We formulated a transmission model comprising both primary routine and maternal immunization. This model was examined to evaluate the long-term epidemiological effects of routine and maternal immunization, together with consequences of potential immune interference scenarios.

RESULTS

 Overall, our model demonstrates that maternal immunization is an effective strategy in reducing the incidence of pertussis in neonates prior to the onset of the primary schedule. However, if maternal antibodies lead to blunting, incidence increases among older age groups. For instance, our model predicts that with 60% routine and maternal immunization coverage and 30% blunting, the incidence among neonates (0-2 months) is reduced by 43%. Under the same scenario, we observe a 20% increase in incidence among children aged 5-10 years. However, the downstream increase in the older age groups occurs with a delay of approximately a decade or more.

CONCLUSIONS

 Maternal immunization has clear positive effects on infant burden of disease, lowering mean infant incidence. However, if maternally derived antibodies adversely affect the immunogenicity of the routine schedule, we predict eventual population-level repercussions that may lead to an overall increase in incidence in older age groups.

Pertussis: Microbiology, Disease, Treatment, and Prevention

Pertussis is a severe respiratory infection caused by Bordetella pertussis, and in 2008, pertussis was associated with an estimated 16 million cases and 195,000 deaths globally. Sizeable outbreaks of pertussis have been reported over the past 5 years, and disease reemergence has been the focus of international attention to develop a deeper understanding of pathogen virulence and genetic evolution of B. pertussis strains. During the past 20 years, the scientific community has recognized pertussis among adults as well as infants and children. Increased recognition that older children and adolescents are at risk for disease and may transmit B. pertussis to younger siblings has underscored the need to better understand the role of innate, humoral, and cell-mediated immunity, including the role of waning immunity. Although recognition of adult pertussis has increased in tandem with a better understanding of B. pertussis pathogenesis, pertussis in neonates and adults can manifest with atypical clinical presentations. Such disease patterns make pertussis recognition difficult and lead to delays in treatment. Ongoing research using newer tools for molecular analysis holds promise for improved understanding of pertussis epidemiology, bacterial pathogenesis, bioinformatics, and immunology. Together, these advances provide a foundation for the development of new-generation diagnostics, therapeutics, and vaccines.

Protecting Newborns Against Pertussis: Treatment and Prevention Strategies

Pertussis is a potentially severe respiratory disease, which affects all age groups from young infants to older adults and is responsible for an estimated 195,000 deaths occurred globally in 2008. Active research is ongoing to better understand the pathogenesis, immunology, and diagnosis of pertussis. For diagnosis, molecular assays (e.g., polymerase chain reaction) for detection of Bordetella pertussis have become more widely available and support improved outbreak detection. In children, pertussis vaccines have been incorporated into routine immunization schedules and deployed for pertussis outbreak control. Lower levels of vaccine coverage are now being observed in communities where vaccine hesitancy is rising. Additionally, recognition that newborn babies are at risk of pertussis in the USA and UK has led to recommendations to immunize pregnant women. Among adolescents and older adults in the USA, Tetanus Toxoid, Reduced Diphtheria Toxoid and Acellular pertussis (Tdap) Vaccines are recommended, but substantial individual- and system-level barriers exist that will make achieving national Healthy People 2020 targets for immunization challenging. Current antimicrobial regimens for pertussis are focused on reducing the severity of disease, reducing rates of sequelae, and minimizing transmission of infection to susceptible individuals. Continued surveillance for pertussis will be important to identify opportunities for reducing young infants' exposure and reducing the impact of outbreaks among school-aged children. Laboratory-based surveillance for newly emerging strains of B. pertussis will be important to identify strains that may evade protection elicited by currently available vaccines. Efforts to develop new-generation pertussis vaccines should be considered now in anticipation of vaccine development programs, which may require ten or more years to deliver a licensed vaccine.

Strategies to decrease pertussis transmission to infants

The Global Pertussis Initiative (GPI) is an expert scientific forum addressing the worldwide burden of pertussis, which remains a serious health issue, especially in infants. This age cohort is at risk for developing pertussis by transmission from those in close proximity. Risk is increased in infants aged 0 to 6 weeks, as they are too young to be vaccinated. Older infants are at risk when their vaccination schedules are incomplete. Infants also bear the greatest disease burden owing to their high risk for pertussis-related complications and death; therefore, protecting them is a high priority. Two vaccine strategies have been proposed to protect infants. The first involves vaccinating pregnant women, which directly protects through the passive transfer of pertussis antibodies. The second strategy, cocooning, involves vaccinating parents, caregivers, and other close contacts, which indirectly protects infants from transmission by preventing disease in those in close proximity. The goal of this review was to present and discuss evidence on these 2 strategies. Based on available data, the GPI recommends vaccination during pregnancy as the primary strategy, given its efficacy, safety, and logistic advantages over a cocoon approach. If vaccination during pregnancy is not feasible, then all individuals having close contact with infants <6 months old should be immunized consistent with local health authority guidelines. These efforts are anticipated to minimize pertussis transmission to vulnerable infants, although real-world effectiveness data are limited. Countries should educate lay and medical communities on pertussis and introduce robust surveillance practices while implementing these protective strategies.

Prevention of pertussis through adult vaccination

Pertussis is a vaccine preventable respiratory infection. Young infants are at high risk of developing severe complications from infection. Despite high rates of pediatric vaccine uptake, there continues to be increases in pertussis cases, likely due to waning immunity from childhood vaccine and increased transmission through adults. Currently, pertussis booster vaccine (Tdap) is recommended for unimmunized adults and for women in the third trimester of each pregnancy; yet adult Tdap coverage remains low. Administering Tdap vaccine at non-traditional vaccination clinics and at sites where adults are accessing care for their children are effective in improving adult Tdap uptake. While most are willing to receive vaccine when recommended by their provider, lack of provider recommendation is a major obstacle to immunization. Future studies to understand barriers to provider vaccine recommendations need to be undertaken to develop interventions to improve adult Tdap vaccine uptake and reduce pertussis infection in the susceptible population.

Updated treatment and prevention guidelines for pertussis

Pertussis, commonly referred to as whooping cough, is one of the top 10 causes of death in children globally despite vaccine availability. Adhering to vaccination guidelines for both the primary childhood series as well as adolescent and adult boosters is crucial in preventing the spread of disease. However, due to vaccine failure, outbreaks occur every 3 to 5 years. As a result, early recognition and prompt treatment are instrumental in controlling the epidemic.

Does tetanus-diphtheria-acellular pertussis vaccination interfere with serodiagnosis of pertussis infection?

An anti-pertussis toxin (PT) IgG enzyme-linked immunosorbent assay (ELISA) was analytically validated for the diagnosis of pertussis at a cutoff of 94 ELISA units (EU)/ml. Little was known about the performance of this ELISA in the diagnosis of adults recently vaccinated with tetanus-diphtheria-acellular pertussis (Tdap) vaccine, which contains PT. The goal of this study was to determine when the assay can be used following Tdap vaccination. A cohort of 102 asymptomatic health care personnel (HCP) vaccinated with Tdap (Adacel; Sanofi Pasteur) were aged 19 to 79 years (median, 47 years) at vaccination. For each HCP, specimens were available for evaluation at 2 to 10 time points (prevaccination to 24 months postvaccination), and geometric mean concentrations (GMC) for the cohort were calculated at each time point. Among 97 HCP who responded to vaccination, a mixed-model analysis with prediction and tolerance intervals was performed to estimate the time at which serodiagnosis can be used following vaccination. The GMCs were 8, 21, and 9 EU/ml at prevaccination and 4 and 12 months postvaccination, respectively. Eight (8%) of the 102 HCP reached antibody titers of ≥94 EU/ml during their peak response, but none had these titers by 6 months postvaccination. The calculated prediction and tolerance intervals were <94 EU/ml by 45 and 75 days postvaccination, respectively. Tdap vaccination 6 months prior to testing did not confound result interpretation. This seroassay remains a valuable diagnostic tool for adult pertussis.