Randomized clinical trial of the safety and immunogenicity of the Tdap vaccine in pregnant Mexican women

Defining and reporting adverse events of special interest in comparative maternal vaccine studies: a systematic review

Introduction

The GAIA (Global Alignment on Immunisation Safety Assessment in Pregnancy) consortium was established in 2014 with the aim of creating a standardised, globally coordinated approach to monitoring the safety of vaccines administered in pregnancy. The consortium developed twenty-six standardised definitions for classifying obstetric and infant adverse events. This systematic review sought to evaluate the current state of adverse event reporting in maternal vaccine trials following the publication of the case definitions by GAIA, and the extent to which these case definitions have been adopted in maternal vaccine safety research.

Methods

A comprehensive search of published literature was undertaken to identify maternal vaccine research studies. PubMed, EMBASE, Web of Science, and Cochrane were searched using a combination of MeSH terms and keyword searches to identify observational or interventional studies that examined vaccine safety in pregnant women with a comparator group. A two-reviewer screening process was undertaken, and a narrative synthesis of the results presented.

Results

14,737 titles were identified from database searches, 435 titles were selected as potentially relevant, 256 were excluded, the remaining 116 papers were included. Influenza vaccine was the most studied (25.0%), followed by TDaP (20.7%) and SARS-CoV-2 (12.9%).Ninety-one studies (78.4%) were conducted in high-income settings. Forty-eight (41.4%) utilised electronic health-records. The majority focused on reporting adverse events of special interest (AESI) in pregnancy (65.0%) alone or in addition to reactogenicity (27.6%). The most frequently reported AESI were preterm birth, small for gestational age and hypertensive disorders. Fewer than 10 studies reported use of GAIA definitions. Gestational age assessment was poorly described; of 39 studies reporting stillbirths 30.8% provided no description of the gestational age threshold.

Conclusions

Low-income settings remain under-represented in comparative maternal vaccine safety research. There has been poor uptake of GAIA case definitions. A lack of harmonisation and standardisation persists limiting comparability of the generated safety data.

Safety and Clinical Benefits of Adacel® and Adacel®-Polio Vaccination in Pregnancy: A Structured Literature Review

Vaccination in pregnancy using a tetanus toxoid, reduced dose diphtheria toxoid, and reduced dose acellular pertussis (Tdap) vaccine is important for prevention of severe pertussis disease in young infants. The objectives of this systematic literature review were to search for original research studies evaluating the vaccine effectiveness, immunogenicity, and safety of Adacel®/Adacel-Polio® used during pregnancy to prevent pertussis disease in young infants. Medical databases used included EMBASE, BIOSIS Previews, and Chemical Abstracts, with search terms related to pregnancy, vaccines/immunization, safety, pertussis, effectiveness/efficacy, and immune response; other potentially eligible reports were included where applicable. Search results were restricted to literature published from 1 January 1995 to 26 July 2021. A total of 2021 articles and 4 other reports were identified for primary review. A total of 49 publications qualified for inclusion after primary and secondary reviews. Effectiveness studies of Adacel or Adacel-Polio given in pregnancy consistently showed high levels of protection from pertussis disease in the newborn (vaccine effectiveness: 91-93%). In immunogenicity studies, the response in pregnant women was consistent with that of non-pregnant women. Infants of mothers vaccinated with Adacel or Adacel-Polio in pregnancy had higher anti-pertussis antibody levels at birth and at 2 months of age compared to infants born to women vaccinated with comparator vaccines, placebo, or those not vaccinated during pregnancy. There was evidence of a slightly decreased response to primary pertussis vaccination in infants of mothers vaccinated with Adacel or Adacel-Polio, but this was not thought to be clinically significant. In safety studies, Adacel or Adacel-Polio vaccination was well tolerated by pregnant woman and not associated with pregnancy, postpartum, or neonatal complications. In conclusion, Adacel or Adacel-Polio vaccination in pregnancy is highly effective in protecting young infants from pertussis disease, with a favorable safety profile for both pregnant women and their infants.

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.

Impact of maternal whole-cell or acellular pertussis primary immunization on neonatal immune response

With the introduction of pertussis immunization for pregnant women in many countries, there has been renewed interest in the impact of whole-cell pertussis vaccine (wP) versus acellular vaccine (aP) on disease control, particularly regarding the best approach for priming. To gather evidence on this topic, we analyzed the impact of aP or wP priming on aP vaccination during pregnancy (aPpreg) in mice. Two-mother vaccination schemes were employed (wP-wP-aPpreg and aP-aP-aPpreg), and the immune response in the mothers and their offspring, as well as the protection of the offspring against Bordetella pertussis challenge, were assessed. Pertussis toxin (PTx)-specific IgG responses were detected in mothers after both the second and third doses, with higher titers after the third dose, regardless of the vaccination schedule. However, a significant reduction in PTx-IgG levels was observed after 22 weeks post aPpreg immunization in mothers with the aP-aP-aPpreg scheme but not in the wP-wP-aPpreg immunized mothers. The aP-aP-aPpreg schedule triggered a murine antibody response mainly to a Th2-profile, while wP-wP-aPpreg induced a Th1/Th2 mixed profile. Both immunization schemes administered to the mothers protected the offspring against pertussis, but the wP-wP-aPpreg vaccination conferred offspring protection in all pregnancies at least up to 20 weeks after receiving the aPpreg-dose. In contrast, the immunity induced by aP-aP-aPpreg began to decline in births that occurred 18 weeks after receiving the aPpreg dose. For the aP-aP-aPpreg scheme, pups born from gestations furthest from aPpreg (+22 weeks) had lower PTx-specific IgG levels than those born closer to the application of the dose during pregnancy. In contrast, for pups born to wP-wP-aPpreg vaccinated mothers, the PTx-specific IgG levels were maintained over time, even for those born at the longest time studied (+22 weeks). It is noteworthy that only the pups born from mothers with aP-aP-aPpreg and receiving a neonatal dose of either aP or wP were more susceptible to B. pertussis infection than mice with only maternal immunity, suggesting interference with the induced immunity (p<0.05). However, it should be noted that mice with maternal immunity, whether vaccinated or not with neonatal doses, are better protected against colonization with B. pertussis than mice without maternal immunity but vaccinated with aP or wP.

Optimization of Timing of Maternal Pertussis Immunization From 6 Years of Postimplementation Surveillance Data in England

BACKGROUND

England's third-trimester maternal pertussis vaccination, introduced in October 2012, was extended to the second trimester in 2016. Maternal vaccination provides high protection against infant disease, but routine second-trimester vaccination has not previously been assessed.

METHODS

National laboratory-confirmed pertussis case surveillance determined vaccination history, maternal vaccination history and hospitalization. Pertussis hospital admissions between 2012 and 2019 were extracted from the Hospital Episode Statistics data set. Vaccine effectiveness (VE) was calculated for pertussis case patients born between October 2012 and September 2018 using the screening method and matching with a nationally representative data set.

RESULTS

Higher coverage was observed after earlier maternal vaccination with approximately 40% of pregnant women vaccinated ≥13 weeks before delivery. Cases and hospitalizations stabilized at low levels in younger infants but remained elevated in older infants, children, and adults. No deaths occurred in infants with vaccinated mothers after 2016. Of 1162 laboratory-confirmed pertussis cases in the study, 599 (52%) were in infants aged <93 days: 463 (77%) with unvaccinated and 136 (23%) with vaccinated mothers. The VE was equivalent in infants with mothers vaccinated at different gestational periods except in those with mothers vaccinated between 7 days before and 41 days after delivery. Children whose mothers were unvaccinated but with vaccination in a previous pregnancy had a VE against disease of 44% (95% confidence interval, 19%-75%). There was no increased disease risk after primary vaccination in children with mothers vaccinated at least 7 days before delivery.

CONCLUSIONS

National policy recommending vaccination in the second trimester increased earlier maternal vaccine uptake with sustained high VE and impact against early infant disease.

Safety and Immunogenicity of Pertussis Vaccine Immunization during Pregnancy: A Meta-Analysis of Randomized Clinical Trials

The objective of this meta-analysis is to assess the safety and immunogenicity of maternal pertussis vaccination based on randomized clinical trials. PubMed, Embase, Cochrane Library, Web of Science, China National Knowledge Internet, and Wan Fang Database were searched from inception up to the 8th of October 2021, using a protocol registered on PROSPERO with no. 42021287717, and a meta-analysis was conducted. We measured pooled geometric mean concentrations (GMCs) for IgG antibodies against pertussis and the incidence of serious adverse events (SAEs). We identified a total of 522 publications, and after a strict screening, we found that 6 RCTs were eligible for our meta-analysis. GMCs were determined with a standardized mean difference (SMD), and the pooled SMD of anti-PT, anti-FHA, and anti-PRN IgG from cord blood were 0.91 (95% CI: 0.58, 1.24), 1.03 (95% CI: (0.70, 1.35)), and 1.55(95% CI: 1.22, 1.88), respectively. The pooled OR of SAEs of women and infants did not show a statistical difference; the pooled ORs were 1.26 (95% CI: 0.78, 2.05); P = 0.35) and 0.61 (95% CI: 0.37, 1.01); p = 0.053), respectively. Infants of immunized women have significantly higher transplacental antibodies for protection against pertussis disease during the first 2 months of life.

Evaluation of Whole-Cell and Acellular Pertussis Vaccines in the Context of Long-Term Herd Immunity

After the pertussis vaccine had been introduced in the 1940s and was shown to be very successful in reducing the morbidity and mortality associated with the disease, the possibility of improving both vaccine composition and vaccination schedules has become the subject of continuous interest. As a result, we are witnessing a considerable heterogeneity in pertussis vaccination policies, which remains beyond universal consensus. Many pertussis-related deaths still occur in low- and middle-income countries; however, these deaths are attributable to gaps in vaccination coverage and limited access to healthcare in these countries, rather than to the poor efficacy of the first generation of pertussis vaccine consisting in inactivated and detoxified whole cell pathogen (wP). In many, particularly high-income countries, a switch was made in the 1990s to the use of acellular pertussis (aP) vaccine, to reduce the rate of post-vaccination adverse events and thereby achieve a higher percentage of children vaccinated. However the epidemiological data collected over the past few decades, even in those high-income countries, show an increase in pertussis prevalence and morbidity rates, triggering a wide-ranging debate on the causes of pertussis resurgence and the effectiveness of current pertussis prevention strategies, as well as on the efficacy of available pertussis vaccines and immunization schedules. The current article presents a systematic review of scientific reports on the evaluation of the use of whole-cell and acellular pertussis vaccines, in the context of long-term immunity and vaccines efficacy.

Vaccination in Pregnancy against Pertussis: A Consensus Statement on Behalf of the Global Pertussis Initiative

Infants are at high risk for severe morbidity and mortality from pertussis disease during early infancy. Vaccination against pertussis in pregnancy has emerged as the ideal strategy to protect infants during these early, vulnerable, first months of life. On 30 November and 1 December 2021, the Global Pertussis Initiative held a meeting that aimed to discuss and review the most up-to-date scientific literature supporting vaccination against pertussis in pregnancy and outstanding scientific questions. Herein, we review the current and historically published literature and summarize the findings as consensus statements on vaccination against pertussis in pregnancy on behalf of the Global Pertussis Initiative.

Protecting the Offspring, the Gift of Maternal Immunization: Current Status and Future Perspectives

Pregnancy is characterized by immunological alterations in pregnant women that permit the growth of a semi-allogenic fetus, resulting in greater susceptibility of childbearing women to infections. Furthermore, due to the immaturity of the immune system of neonates, a protection gap is present in early life, leaving neonates and infants vulnerable to infectious diseases with increased morbidity and mortality. Maternal immunization against influenza, pertussis, and, in the context of the COVID-19 pandemic, SARS-CoV-2 has been implemented in several countries, with beneficial effects on both the mother and the offspring. The main protective mechanism of vaccination during pregnancy is transplacental transfer of maternal antibodies. However, recent evidence has implied that the fetal immune system may be influenced beyond passive immunity. This review sheds light on the current status of the routinely administered vaccinations during pregnancy, focusing on the impact of maternal immunization on the priming of the fetal immune system and suggesting future perspectives for the optimization of vaccination strategies.

The optimal strategy for pertussis vaccination: a systematic review and meta-analysis of randomized control trials and real-world data

OBJECTIVE

Severe pertussis infection has been reported in infants before receiving routine immunization series. This problem could be solved by vaccinating mothers during pregnancy or children at birth. This study aimed to conduct a systematic review and meta-analysis of randomized controlled trials (RCTs) and real-world evidence to evaluate the optimal strategy for pertussis vaccination.

DATA SOURCES

PubMed, Embase, and the Cochrane Library databases were searched until December 2020.

STUDY ELIGIBILITY CRITERIA

RCTs, cohort studies, case-control studies, and case series were included if they investigated the efficacy, immunogenicity, and safety of acellular pertussis vaccine during pregnancy and at birth.

METHODS

Number of pertussis cases, severe adverse events (SAEs), and pertussis antibody concentration in infants before and after they receive routine vaccination series were extracted and random-effect model was used to pool the analyses.

RESULTS

Overall, 29 studies were included. Our meta-analysis revealed that pertussis immunization during pregnancy significantly increased the concentrations of 3 pertussis antibodies and reduced the incidence rates of infected infants below 3 months of age (odds ratio, 0.22; 95% confidence interval, 0.14-0.33). Similarly, infants vaccinated at birth had higher levels of pertussis antibody than those who were not. No significant difference in rates of severe adverse events was seen in all vaccination groups (during pregnancy [risk ratio, 1.18; 95% confidence interval, 0.76-1.82] and at birth [risk ratio, 0.72; 95% confidence interval, 0.34-1.54]).

CONCLUSION

Pertussis vaccination during pregnancy could protect infants against pertussis disease before the routine vaccination. Pertussis immunization at birth would be an alternative for infants whose mothers did not receive pertussis vaccines during pregnancy.

Safety of vaccines used for routine immunization in the United States: An updated systematic review and meta-analysis

BACKGROUND

Understanding the safety of vaccines is critical to inform decisions about vaccination. Our objective was to conduct a systematic review of the safety of vaccines recommended for children, adults, and pregnant women in the United States.

METHODS

We searched the literature in November 2020 to update a 2014 Agency for Healthcare Research and Quality review by integrating newly available data. Studies of vaccines that used a comparator and reported the presence or absence of key adverse events were eligible. Adhering to Evidence-based Practice Center methodology, we assessed the strength of evidence (SoE) for all evidence statements. The systematic review is registered in PROSPERO (CRD42020180089).

RESULTS

Of 56,603 reviewed citations, 338 studies reported in 518 publications met inclusion criteria. For children, SoE was high for no increased risk of autism following measles, mumps, and rubella (MMR) vaccine. SoE was high for increased risk of febrile seizures with MMR. There was no evidence of increased risk of  intussusception with rotavirus vaccine at the latest follow-up (moderate SoE), nor of diabetes (high SoE). There was no evidence of increased risk or insufficient evidence for key adverse events for newer vaccines such as 9-valent human papillomavirus and meningococcal B vaccines. For adults, there was no evidence of increased risk (varied SoE) or insufficient evidence for key adverse events for the new adjuvanted inactivated influenza vaccine and recombinant adjuvanted zoster vaccine. We found no evidence of increased risk (varied SoE) for key adverse events among pregnant women following tetanus, diphtheria, and acellular pertussis vaccine, including stillbirth (moderate SoE).

CONCLUSIONS

Across a large body of research we found few associations of vaccines and serious key adverse events; however, rare events are challenging to study. Any adverse events should be weighed against the protective benefits that vaccines provide.

Impact of maternal diphtheria-tetanus-acellular pertussis vaccination on pertussis booster immune responses in toddlers: Follow-up of a randomized trial

BACKGROUND

Transplacentally transferred antibodies induced by maternal pertussis vaccination interfere with infant immune responses to pertussis primary vaccination. We evaluated whether this interference remains in toddlers after booster vaccination.

METHODS

In a prior phase IV, observer-blind, placebo-controlled, randomized study (NCT02377349), pregnant women in Australia, Canada and Europe received intramuscular tetanus-reduced-antigen-content diphtheria-three-component acellular pertussis vaccine (Tdap group) or placebo (control group) at 27^0/7-36^6/7 weeks' gestation, with crossover immunization postpartum. Their infants were primed (study NCT02422264) and boosted (at 11-18 months; current study NCT02853929) with diphtheria-tetanus-three-component acellular pertussis-hepatitis B virus-inactivated poliovirus/Haemophilus influenzae type b vaccine (DTaP-HepB-IPV/Hib) and 13-valent pneumococcal conjugate vaccine. Immunogenicity before and after booster vaccination, and reactogenicity and safety of the booster were evaluated descriptively.

RESULTS

263 (Tdap group) and 277 (control group) toddlers received a DTaP-HepB-IPV/Hib booster. Pre-booster vaccination, observed geometric mean concentrations (GMCs) for the three pertussis antigens and diphtheria were 1.4-1.5-fold higher in controls than in the Tdap group. No differences were observed for the other DTaP-HepB-IPV/Hib antigens. One month post-booster vaccination, booster response rates for pertussis antigens were ≥ 92.1% and seroprotection rates for the other DTaP-HepB-IPV/Hib antigens were ≥ 99.2% in both groups (primary objective). Higher post-booster GMCs were observed in controls versus the Tdap group for anti-filamentous hemagglutinin (1.2-fold), anti-pertussis toxoid (1.5-fold) and anti-diphtheria (1.4-fold). GMCs for the other DTaP-HepB-IPV/Hib antigens were similar between groups. Serious adverse events were reported for three toddlers (controls, not vaccination-related). One death occurred pre-booster (Tdap group, not vaccination-related).

CONCLUSIONS

As a consequence of interference of maternal pertussis antibodies with infant immune responses to pertussis primary vaccination, pertussis antibody concentrations were still lower in toddlers from Tdap-vaccinated mothers before DTaP-HepB-IPV/Hib booster vaccination. After the booster, antibody concentrations were lower for filamentous hemagglutinin and pertussis toxoid but not for pertactin. The clinical significance of this interference requires further evaluation.

CLINICAL TRIAL REGISTRATION

ClinicalTrials.gov: NCT02853929.

Global Perspectives on Immunization During Pregnancy and Priorities for Future Research and Development: An International Consensus Statement

Immunization during pregnancy has been recommended in an increasing number of countries. The aim of this strategy is to protect pregnant women and infants from severe infectious disease, morbidity and mortality and is currently limited to tetanus, inactivated influenza, and pertussis-containing vaccines. There have been recent advancements in the development of vaccines designed primarily for use in pregnant women (respiratory syncytial virus and group B Streptococcus vaccines). Although there is increasing evidence to support vaccination in pregnancy, important gaps in knowledge still exist and need to be addressed by future studies. This collaborative consensus paper provides a review of the current literature on immunization during pregnancy and highlights the gaps in knowledge and a consensus of priorities for future research initiatives, in order to optimize protection for both the mother and the infant.

Active SMS-based surveillance of adverse events following immunisation with influenza and pertussis-containing vaccines in Australian pregnant women using AusVaxSafety

BACKGROUND

Maternal immunisation is important to protect both mother and baby, but safety concerns can lead to low uptake. AusVaxSafety participant-based surveillance actively monitors adverse events following immunisation (AEFI) in Australia. We aimed to analyse AEFI in the days following vaccination with seasonal inactivated influenza vaccine (IIV) and/or reduced antigen diphtheria-tetanus-acellular pertussis vaccine (dTpa) in pregnant women in Australia.

METHODS

De-identified AEFI reports were solicited from vaccine recipients via automated SMS survey (using SmartVax software) following routine vaccination with IIV and/or dTpa at 219 national sentinel surveillance sites from 2015 to 2018. AEFI rates were compared by vaccine group (IIV alone, dTpa alone, or IIV and dTpa together), vaccine brand, trimester (IIV only) and vaccination period (April to August 2016-2018; IIV only). Women who had two vaccination encounters during surveillance were identified and AEFI rates compared for each dose.

RESULTS

Among 13,758 participants, overall AEFI rates were lower following IIV (4.9%) than dTpa (6.4%) or IIV and dTpa given concomitantly (7.4%). The AEFI profile was similar for both vaccines, with injection site reactions, tiredness, and headache most commonly reported. Injection site pain and swelling/redness were significantly more common in women who received dTpa than IIV. Reports of medical attendance following immunisation were similar (0.3%) for each vaccine group. AEFI rates did not differ by IIV brand (FluQuadri®, Fluarix® Tetra), dTpa brand (Boostrix®, Adacel®), or by trimester. Among women with sequential dTpa vaccinations, 6.0% (7/116) had an AEFI following their second dTpa dose.

CONCLUSIONS

Self-reported AEFI rates did not differ by trimester (IIV), or by vaccine brand (IIV or dTpa). Concomitant influenza and pertussis vaccination was associated with more frequent, but low rates of minor, expected AEFI. These real world 'citizen science-based' data provide further reassuring evidence of the safety of maternal vaccination.

Immune interference (blunting) in the context of maternal immunization with Tdap-containing vaccines: is it a class effect?

INTRODUCTION

Maternal immunization with reduced antigen content tetanus-diphtheria-acellular pertussis (Tdap)-containing vaccines has been recommended to prevent infant pertussis. However, maternal antibodies may interfere with infant responses to routine immunization with diphtheria-tetanus-acellular pertussis (DTaP)-containing vaccines, raising concerns of suboptimal protection after infant vaccination. We performed a narrative literature review to assess whether blunting occurs regardless of the manufacturer of maternal and infant vaccines. Because internationally agreed correlates of protection are lacking, the clinical significance of blunting is not yet fully understood. We have reviewed the evidence available to date.

AREAS COVERED

Thirteen studies that evaluated blunting after maternal immunization and infant primary/booster series were identified. Blunting was observed with various combinations of Tdap- and DTaP-containing vaccines for maternal and pediatric immunization. Studies assessing the effectiveness of maternal Tdap immunization beyond the primary infant immunization series in England and in the United States suggested no evidence of a clinically relevant blunting effect so far.

EXPERT COMMENTARY

This review indicates that the phenomenon of blunting does not depend on the manufacturer/brand of the pertussis-containing vaccines used for immunizing mothers or children. Currently, there is no epidemiological evidence that children whose mothers received Tdap are at increased risk of pertussis after pediatric vaccinations, although longer follow-up is required.

Vertically Transferred Immunity in Neonates: Mothers, Mechanisms and Mediators

Over the last years, an increasing number of outbreaks of vaccine-preventable infectious diseases has been reported. Besides elderly and immunocompromised individuals, newborns and small infants are most susceptible to infections, as their immune system is still immature. This vulnerability during infancy can be mitigated by the transplacental transfer of pathogen-specific antibodies and other mediators of immunity from mother to the fetus during pregnancy, followed postnatally by breast milk-derived immunity. Since this largely antibody-mediated passive immunity can prevent the newborn from infections, neonatal immunity depends strongly on the maternal concentration of respective specific antibodies during pregnancy. If titers are low or wane rapidly after birth, the protection transferred to the child may not be sufficient to prevent disease. Moreover, emerging concepts propose that mothers may transfer active immunity to the newborns via vertical transfer of pathogen-specific T cells. Overall, a promising strategy to augment and prolong neonatal immunity is to vaccinate the mother before or during pregnancy in order to boost maternal antibody concentrations or availability of specific T cells. Hence, a large number of pre-and postconceptional vaccine trials have been carried out to test and confirm this concept. We here highlight novel insights arising from recent research endeavors on the influence of prenatal maternal vaccination against pathogens that can pose a threat for newborns, such as measles, pertussis, rubella and influenza A. We delineate pathways involved in the transfer of specific maternal antibodies. We also discuss the consequences for children's health and long-term immunity resulting from an adjustment of prenatal vaccination regimes.

Are all vaccines safe for the pregnant traveller? A systematic review and meta-analysis

Pregnant travellers and their offspring are vulnerable to severe outcomes following a wide range of infections. Vaccine-preventable diseases can have a particularly severe course in pregnant women, but little is known about the safety of travel vaccines in pregnant women. We performed a systematic review of all published literature concerning the safety of vaccines frequently given to travellers such as yellow fever, MMR (mumps, measles and rubella), influenza, Tdap (tetanus, diphtheria and pertussis), meningococcus, hepatitis A and B, rabies, polio, typhoid fever, tick-borne encephalitis and Japanese encephalitis vaccines. We included case series, cohort studies and randomized controlled trials (RCTs). For the meta-analysis, we included only RCTs that compared the administration of a vaccine to placebo or to no vaccine. Outcome measures included severe systemic adverse events, maternal outcomes related to the course of pregnancy, neonatal outcomes and local adverse events. We calculated the risk ratio and its 95% confidence interval as the summary measure. The safety of influenza vaccine is supported by high-quality evidence. For Tdap vaccine, no evidence of any harm was found in the meta-analysis of RCTs. A slight increase in chorioamnionitis rate was reported in 3 out of 12 observational studies. However, this small possible risk is far outweighed by a much larger benefit in terms of infant morbidity and mortality. Meningococcal vaccines are probably safe during pregnancy, as supported by RCTs comparing meningococcal vaccines to other vaccines. Data from observational studies support the safety of hepatitis A, hepatitis B and rabies vaccines, as well as that of the live attenuated yellow fever vaccine. We found little or no data about the safety of polio, typhoid, Japanese encephalitis, tick-borne encephalitis and MMR vaccines during pregnancy.

Safety and effectiveness of acellular pertussis vaccination during pregnancy: a systematic review

Background

Infants < 3 months of age are at highest risk for developing severe complications after pertussis. The majority of pregnant women has low concentrations of pertussis-specific antibodies and thus newborns are insufficiently protected by maternally transferred antibodies. Acellular pertussis vaccination during pregnancy was recently implemented in various countries. Here, we assessed the evidence for safety and effectiveness of pertussis vaccination during pregnancy.

Methods

We searched Medline, Embase, and ClinicalTrials.gov from January 1st 2010 to January 10th 2019. We assessed risk of bias (ROB) using the Cochrane ROB tool and ROBINS-I. We evaluated the quality of evidence using the GRADE approach.

Results

We identified 1273 articles and included 22 studies (14 for safety; 8 for effectiveness), comprising 1.4 million pregnant women in safety studies and 855,546 mother-infant-pairs in effectiveness studies. No significant differences between vaccinated and unvaccinated women and their infants were observed for safety outcomes with the exception of fever and chorioamnionitis. Compared to no vaccination, three studies showed a significantly increased relative risk for the presence of the ICD-9 code for chorioamnionitis in electronic patient data after pertussis vaccination. However, no study reported an increased risk for clinical sequelae of chorioamnionitis after vaccination during pregnancy, such as preterm birth or neonatal intensive care unit admission. Vaccine effectiveness against pertussis in infants of immunized mothers ranged from 69 to 91% for pertussis prevention, from 91 to 94% for prevention of hospitalization and was 95% for prevention of death due to pertussis. Risk of bias was serious to critical for safety outcomes and moderate to serious for effectiveness outcomes. GRADE evidence quality was moderate to very low, depending on outcome.

Conclusion

Although an increased risk for a diagnosis of fever and chorioamnionitis was detected in pregnant women after pertussis vaccination, there was no association with a higher frequency of clinically relevant sequelae. Vaccine effectiveness for prevention of infant pertussis, hospitalization and death is high. Pertussis vaccination during pregnancy has an overall positive benefit-risk ratio. In view of the overall quality of available evidence ongoing surveillance of chorioamnionitis and its potential sequelae is recommended when pertussis vaccination in pregnancy is implemented.

Trial registration

PROSPERO CRD42018087814, CRD42018090357.

Safety of Maternal Immunization Against Pertussis: A Systematic Review

The WHO recommends vaccination of all children against pertussis. However, newborn infants remain vulnerable to infection. Pertussis vaccination during pregnancy has been introduced in several countries to protect newborns via transplacental transfer of maternal pertussis antibodies to the infant. We reviewed the impact of maternal pertussis vaccination on the health of pregnant women, the developing fetus, and health of the newborn. We searched PubMed/MEDLINE, EMBASE, Scopus (Elsevier), Cochrane Database of Systematic Reviews, ProQuest, and Science Direct to identify studies that assessed the safety of maternal pertussis vaccination. Twenty-seven English language publications published between January 1995 and December 2018 were included in this review. Pregnant women receiving pertussis vaccines did not have increased rates of systemic or local reactions. There were no safety concerns with repeat vaccination with other tetanus-containing vaccines or their concomitant administration with influenza vaccines. Maternal pertussis vaccination did not adversely affect pregnancy, birth or neonatal outcomes. This review confirms the safety of maternal pertussis vaccination during pregnancy. FUNDING: Sanofi Pasteur. Plain language summary available for this article.

Immunological and Clinical Benefits of Maternal Immunization Against Pertussis: A Systematic Review

Infants are vulnerable to pertussis infection particularly before initiation of pertussis vaccination. Maternal pertussis vaccination during pregnancy has been introduced in a number of countries in order to confer on young infants indirect protection from the disease through transplacental transfer of maternal antibodies. We reviewed the evidence on the immunogenicity and efficacy of maternal pertussis vaccination during pregnancy. A systematic search of PubMed/MEDLINE, EMBASE, Scopus, Cochrane Database of Systematic Reviews, ProQuest, and Science Direct was undertaken to identify studies published between January 1995 and December 2018. This review was not specific to any particular pertussis vaccine but included applicable data on available pertussis vaccines administered to pregnant women. The search identified 40 publications for inclusion in this review. Vaccination during pregnancy elicited robust maternal immune responses against all vaccine antigens and resulted in high placental transfer of pertussis antibodies to the infant that persisted well beyond delivery. Vaccination during the second or early third trimesters was considered ideal for antibody quantity and functionality. Although blunting of immune responses to some antigens in the primary immunization series was documented in neonates born to women vaccinated during pregnancy, there was no apparent adverse effect on vaccine efficacy. Multiple studies conducted in diverse settings have confirmed the effectiveness of maternal pertussis vaccination during pregnancy in preventing pertussis in infants prior to receipt of their first primary vaccine dose and beyond. These findings collectively underscore the value of maternal pertussis vaccination during pregnancy in protecting vulnerable infants too young to be vaccinated.Funding Sanofi Pasteur.Plain Language Summary Plain language summary available for this article.

Immunogenicity, transplacental transfer of pertussis antibodies and safety following pertussis immunization during pregnancy: Evidence from a randomized, placebo-controlled trial

BACKGROUND

Pertussis immunization during pregnancy is recommended in many countries. Data from large randomized controlled trials are needed to assess the immunogenicity, reactogenicity and safety of this approach.

METHODS

This phase IV, observer-blind, randomized, placebo-controlled, multicenter trial assessed immunogenicity, transplacental transfer of maternal pertussis antibodies, reactogenicity and safety of a reduced-antigen-content diphtheria-tetanus-three-component acellular pertussis vaccine (Tdap) during pregnancy. Women received Tdap or placebo at 27-36 weeks' gestation with crossover ≤ 72-hour-postpartum immunization. Immune responses were assessed before the pregnancy dose and 1 month after, and from the umbilical cord at delivery. Superiority (primary objective) was reached if the lower limits of the 95% confidence intervals (CIs) of the pertussis geometric mean concentration (GMC) ratios (Tdap/control) in cord blood were ≥ 1.5. Solicited and unsolicited adverse events (AEs) and pregnancy-/neonate-related AEs of interest were recorded.

RESULTS

687 pregnant women were vaccinated (Tdap: N = 341 control: N = 346). Superiority of the pertussis immune response (maternally transferred pertussis antibodies in cord blood) was demonstrated by the GMC ratios (Tdap/control): 16.1 (95% CI: 13.5-19.2) for anti-filamentous hemagglutinin, 20.7 (15.9-26.9) for anti-pertactin and 8.5 (7.0-10.2) for anti-pertussis toxoid. Rates of pregnancy-/neonate-related AEs of interest, solicited general and unsolicited AEs were similar between groups. None of the serious AEs reported throughout the study were considered related to maternal Tdap vaccination.

CONCLUSIONS

Tdap vaccination during pregnancy resulted in high levels of pertussis antibodies in cord blood, was well tolerated and had an acceptable safety profile. This supports the recommendation of Tdap vaccination during pregnancy to prevent early-infant pertussis disease.

CLINICAL TRIAL REGISTRATION

ClinicalTrials.gov: NCT02377349.

Impact of tetanus-diphtheria-acellular pertussis immunization during pregnancy on subsequent infant immunization seroresponses: follow-up from a large randomized placebo-controlled trial

BACKGROUND

Pertussis immunization during pregnancy results in high pertussis antibody concentrations in young infants but may interfere with infant immune responses to post-natal immunization.

METHODS

This phase IV, multi-country, open-label study assessed the immunogenicity and safety of infant primary vaccination with DTaP-HepB-IPV/Hib and 13-valent pneumococcal conjugate vaccine (PCV13). Enrolled infants (6-14 weeks old) were born to mothers who were randomized to receive reduced-antigen-content diphtheria-tetanus-three-component acellular pertussis vaccine (Tdap group) or placebo (control group) during pregnancy (27^0/7-36^6/7 weeks' gestation) with crossover immunization postpartum. All infants received 2 or 3 DTaP-HepB-IPV/Hib and PCV13 doses according to national schedules. Immunogenicity was assessed in infants pre- and 1 month post-primary vaccination. The primary objective was to assess seroprotection/vaccine response rates for DTaP-HepB-IPV/Hib antigens 1 month post-primary vaccination.

RESULTS

601 infants (Tdap group: 296; control group: 305) were vaccinated. One month post-priming, seroprotection rates were 100% (diphtheria; tetanus), ≥98.5% (hepatitis B), ≥95.9% (polio) and ≥94.5% (Hib) in both groups. Vaccine response rates for pertussis antigens were significantly lower in infants whose mothers received pregnancy Tdap (37.5-77.1%) versus placebo (90.0-99.2%). Solicited and unsolicited adverse event rates were similar between groups. Serious adverse events occurred in 2.4% (Tdap group) and 5.6% (control group) of infants, none were vaccination-related.

CONCLUSIONS

Pertussis antibodies transferred during pregnancy may decrease the risk of pertussis infection in the first months of life but interfere with the infant's ability to produce pertussis antibodies, the clinical significance of which remains unknown. Safety and reactogenicity results were consistent with previous experience.

CLINICAL TRIAL REGISTRATION

ClinicalTrials.gov: NCT02422264.

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.

The Effect of Maternal Immunisation During Pregnancy on Infant Vaccine Responses

INTRODUCTION

Immunisation during pregnancy to protect infants against tetanus, pertussis and influenza is recommended in many countries. However, maternal antibodies can interfere with infant vaccine responses. We investigated the effect of antenatal diphtheria-tetanus-acellular pertussis (dTpa) and trivalent inactivated influenza (TIV) immunisation on specific and heterologous antibody responses to routine immunisations given in the first year of life.

METHODS

In total, 471 healthy infants were included. At 7 and 13 months of age, antibodies to the primary course of routine vaccines given at 6 weeks, 4 and 6 months of age (pertussis (pertussis toxin (PT), filamentous haemagglutinin (FHA), pertactin (PRN)), polio (type 1, 2, 3), Haemophilus influenzae type b (Hib), pneumococcus (serotype 1, 3, 4, 5, 6A, 6B, 7F, 9V, 14, 18C, 19A, 19F, 23F)) were measured, and at 13 months of age, antibodies to the 12-month routine vaccines (Hib, meningococcus C, measles, mumps and rubella). The seroprotection rates for each vaccine and the geometric mean concentrations (GMC) of antibodies were compared between infants whose mothers did or did not receive dTpa or TIV immunisation during pregnancy.

RESULTS

A total of 369 infants were included in the final analysis. Maternal dTpa immunisation was associated with reduced antibody responses to both specific (diphtheria and pertussis) and heterologous (polio and pneumococcus) vaccine antigens. This effect was stronger for persistence of antibodies at 13 months of age than it was at 7 months of age. At 7 months of age, adjusted average antibody concentrations were significantly lower for diphtheria, pertussis (PT, FHA, PRN) and polio type 2, and at 13 months of age, for diphtheria, pertussis (PT, FHA, PRN), polio type 1-3 and pneumococcal serotypes 1, 4, 5, 6A, 6B, 7F, 18C and 23F. Additionally, at 13 months of age, seroprotection rates for diphtheria, PT, pneumococcal serotype 1, 6A and 6B were significantly lower in infants after maternal dTpa immunisation. In contrast, for Hib, in infants with maternal dTpa immunisation, the adjusted average antibody concentration and the seroprotection rate were higher, particularly at 7 months of age. Maternal TIV immunisation had minimal effect on infant vaccine responses.

CONCLUSION

Whilst maternal immunisation protects infants in the first few months of life, it might interfere with both specific and heterologous (unrelated) vaccines responses in infants.

RESEARCH IN CONTEXT

Evidence before this study: Maternal immunisation during pregnancy helps to protect infants during the period before they complete their primary immunisations. It has been proven to be safe and beneficial. However, pre-existing maternal antibodies can influence antibody responses following infant immunisation, an effect called 'blunting'. Previous studies have investigated the influence of dTpa but not influenza immunisation during pregnancy on infant vaccine responses. The majority of studies investigated antibody concentrations only to the specific vaccine antigens included in the maternal immunisation, and there is scarce data available on heterologous vaccine responses, particularly pneumococcal responses.Added value of this study: In this study, we have shown that maternal dTpa immunisation during pregnancy is associated with reduced antibody responses to both specific (diphtheria and pertussis) and heterologous (polio and pneumococcus) vaccine antigens. This effect is stronger for persistence of antibodies at 13 months of age than after primary immunisation at 7 months of age. In contrast, for Hib, in infants with maternal dTpa immunisation, antibody concentrations are higher, particularly at 7 months of age. Maternal TIV immunisation has minimal effect on infant vaccine responses.Implications of all the available evidence: Whilst maternal immunisation protects infants in the first few months of life, it might interfere with both specific and heterologous (unrelated) vaccines responses in infants. As most vaccines induce very high antibody responses, small differences in antibody concentrations may not be of clinical significance. However, since maternal immunisation during pregnancy also influences seroprotection rates, strategies, such as additional booster doses in the second year of life, particularly for pertussis and pneumococcus, might need to be considered to address this.

'Links2HealthierBubs' cohort study: protocol for a record linkage study on the safety, uptake and effectiveness of influenza and pertussis vaccines among pregnant Australian women

INTRODUCTION

Pregnant women and infants are at risk of severe influenza and pertussis infection. Inactivated influenza vaccine (IIV) and diphtheria-tetanus-acellular pertussis vaccine (dTpa) are recommended during pregnancy to protect both mothers and infants. In Australia, uptake is not routinely monitored but coverage appears sub-optimal. Evidence on the safety of combined antenatal IIV and dTpa is fragmented or deficient, and there remain knowledge gaps of population-level vaccine effectiveness. We aim to establish a large, population-based, multi-jurisdictional cohort of mother-infant pairs to measure the uptake, safety and effectiveness of antenatal IIV and dTpa vaccines in three Australian jurisdictions. This is a first step toward assessing the impact of antenatal vaccination programmes in Australia, which can then inform government policy with respect to future strategies in national vaccination programmes. METHODS AND ANALYSIS: 'Links2HealthierBubs' is an observational, population-based, retrospective cohort study established through probabilistic record linkage of administrative health data. The cohort includes births between 2012 and 2017 (~607 605 mother-infant pairs) in jurisdictions with population-level antenatal vaccination and health outcome data (Western Australia, Queensland and the Northern Territory). Perinatal data will be the reference frame to identify the cohort. Jurisdictional vaccination registers will identify antenatal vaccination status and the gestational timing of vaccination. Information on maternal, fetal and child health outcomes will be obtained from hospitalisation and emergency department records, notifiable diseases databases, developmental anomalies databases, birth and mortality registers.

ETHICS AND DISSEMINATION

Ethical approval was obtained from the Western Australian Department of Health, Curtin University, the Menzies School of Health Research, the Royal Brisbane and Women's Hospital, and the West Australian Aboriginal Health Ethics Committees. Research findings will be disseminated in peer-reviewed journals, at scientific meetings, and may be incorporated into communication materials for public health agencies and the public.

Third-Trimester Maternal Vaccination Against Pertussis and Pertussis Antibody Concentrations

OBJECTIVE

To compare pertussis antibody concentrations in maternal venous serum (at the time of delivery) and umbilical cord arterial serum among women vaccinated with the tetanus toxoid, reduced diphtheria toxoid, and acellular pertussis (Tdap) vaccine from either 27-30 6/7 weeks of gestation or from 31-35 6/7 weeks of gestation.

METHODS

We conducted a prospective cohort study of pregnant women divided into two groups based on when Tdap was administered: 27-30 6/7 weeks of gestation and 31-35 6/7 weeks of gestation. Paired maternal and umbilical cord samples were obtained at the time of delivery to determine immunoglobulin G (IgG) concentrations to pertussis toxin and pertactin.

RESULTS

Eighty-eight pregnant women were enrolled. Cord serum pertussis toxin IgG concentrations were approximately twice maternal serum pertussis toxin IgG concentrations (91.6 vs 48.6 enzyme-linked immunoassay [ELISA] units/mL, P<.01) and were significantly correlated (Pearson correlation coefficient=0.85, P<.01). There was no significant difference in maternal serum pertussis toxin IgG concentrations (48.6 vs 48.6 ELISA units/mL, P=.99), cord serum pertussis toxin IgG concentrations (92.1 vs 90.7 ELISA units/mL, P=.95), and cord serum pertactin IgG concentrations (798 vs 730 international units/mL, P=.73) between the two groups. Furthermore, there was no correlation between time from vaccination to delivery and these three parameters. Cord serum pertussis toxin IgG concentrations were greater than 10 ELISA units/mL (ie, in the protective range) in 87% and 97% of those vaccinated from 27-30 6/7 weeks of gestation and from 31-35 6/7 weeks of gestation, respectively (P=.13).

CONCLUSION

Maternal vaccination against pertussis between 27 and 36 weeks of gestation was associated with a high percentage of newborns with antibody concentrations conferring protection and did not vary by gestational age at vaccination.

Review of vaccination in pregnancy to prevent pertussis in early infancy

Maternal pertussis vaccination has been introduced in several countries to protect infants from birth until routine infant vaccination takes place. This review assesses existing evidence on the effectiveness and safety of immunization in pregnancy. The search was finalized in April 2017 and was based on searches using several databases. The selection criteria included any experimental or observational study reporting on the immunogenicity, effectiveness or safety of vaccination with a pertussis-containing vaccine in pregnant women and their infants. Following de-duplication and exclusions, we identified 8395 studies, which were reduced to 46 for inclusion. The overall risk of bias was low, with the exception of some early studies and pharmacovigilance safety data. The evidence demonstrates efficient transplacental transfer of maternal antibodies in infants whose mothers were vaccinated with Tdap or Tdap/IPV in pregnancy, with good evidence that this protects against disease in young infants. Safety studies covering more than 150 000 women vaccinated mostly in the late second or third trimesters are generally consistent and provide reassurance of no significant increased risk of recognized maternal conditions or of adverse events (including congenital anomalies) in infants born to vaccinated women. The clinical significance of reduced seroconversion to pertussis following routine immunization is not yet clear, but no increased risk of pertussis in infants whose mothers were vaccinated in pregnancy was found following primary immunizations in North American and English studies. Most post-booster studies suggest that any blunting effect is short-lived and that longer-term protection in infants from active immunization is not compromised.

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.

Pertussis epidemiology in Argentina: TRENDS after the introduction of maternal immunisation

Data on the impact of the recently recommended maternal pertussis vaccination are promising, but still insufficient to universalise this approach. We thus compared the epidemiological data prior to the implementation of this vaccination strategy in Argentina (2012) with the figures reported after 2012. During that 2010–2016 period, two outbreaks occurred, one in 2011 and another in 2016. In the former, the incidence was 6.9/100 000 inhabitants and the case-fatality rate 2.6%. Thereafter, a decline in incidence was detected until 2014. During 2015 and 2016 an increase in the incidence transpired, but this rise was fortunately not accompanied by one in the case fatality ratio. Indeed, in 2016 the case fatality ratio was the lowest (0.6%). Moreover, during the 2016 outbreak, the incidence (3.9/100 000 inhabitants) and the case severity detected in the most vulnerable population (infants 0–2 months) were both lower than those in 2011. Consistent with this pattern, in 2016, in the most populated province of Argentina (Buenos Aires), the case percentage with laboratory-positive results indicating a high number of symptoms (59.1% of the total cases) diminished compared with that detected in the 2011 outbreak without maternal immunisation (71.9%). Using the mathematical model of pertussis transmission we previously designed, we assessed the effect of vaccination during pregnancy on infant incidence. From comparisons between the epidemiological data made through calculations, emerged the possibility that vaccinating women during pregnancy would benefit the infants beyond age 2 months, specifically in the 2–12-month cohort.

Antibodies to Bordetella pertussis antigens in maternal and cord blood pairs: a Thai cohort study

Background

Pertussis is a vaccine-preventable disease, yet an increasing incidence of pertussis occurs in many countries. Thailand has a long-standing pertussis vaccination policy, therefore most expectant mothers today had received vaccines as children. The resurgence of pertussis among Thai infants in recent years led us to examine the pre-existing antibodies to Bordetella pertussis antigens in a cohort of 90 pregnant women.

Methods

We evaluated the IgG to the Pertussis toxin (PT), filamentous hemagglutinin (FHA) and pertactin (PRN) in maternal and cord blood sera using commercial enzyme-linked immunosorbent assays (ELISA).

Results

When values of >10 IU/ml were accepted as potential protective concentrations, we found that the percentages of unprotected infants were 73.3%, 43.3% and 75.5% for anti-PT, anti-FHA and anti-PRN IgG, respectively.

Discussion

These results may explain the susceptibility for pertussis among newborn infants in Thailand and support the requirement for a pertussis booster vaccine during pregnancy, which may contribute to the passive seroprotection among newborns during the first months of life.