Tdap vaccine effectiveness in adolescents during the 2012 Washington State pertussis epidemic

A reduced-dose recombinant pertussis vaccine booster in Thai adolescents: a phase 2/3, observer-blinded, randomised controlled, non-inferiority trial

BACKGROUND

A resurgence of pertussis has increased the demand for low-cost vaccines. The aim of this study was to test the immunogenicity of a booster acellular monovalent pertussis vaccine containing reduced-dose (2 μg) recombinant pertussis toxin (PT) and 5 μg filamentous haemagglutinin (FHA; apgen) against a version of apgen containing tetanus and reduced-dose diphtheria toxoids (Tdapgen) and a licensed vaccine containing chemically detoxified PT and FHA combined with tetanus toxoid and reduced-dose diphtheria toxoid (Tdapchem).

METHODS

This phase 2/3, observer-blinded, randomised, controlled, non-inferiority trial was done in adolescents aged 9-17 years at two clinical research centres in Bangkok and Pathum Thani, Thailand. Eligible participants were screened and randomly assigned (1:1:1) to receive one booster dose of apgen, Tdapgen, or Tdapchem vaccine. Participants were followed up until day 336 post-immunisation. The primary endpoint was non-inferior seroconversion rates in Tdapgen and Tdapchem vaccine groups, with seroconversion rate defined as the proportion of participants with at least a four-fold increase on day 28 post-immunisation relative to baseline of anti-PT and anti-FHA IgG. The non-inferiority for seroconversion rates of anti-PT and anti-FHA IgG was defined as the lower bound of the two-sided 95% CI of the seroconversion rate for Tdapgen compared with Tdapchem exceeding -10%. Immunogenicity was analysed in the per-protocol population. All safety data were collected, and the prevalence of adverse events was analysed in the intention-to-treat population. This trial was registered on the Thai Clinical Trial Registry (TCTR20181031001).

FINDINGS

Between June 18, and Aug 3, 2019, 450 adolescents (mean age 12·1 years, SD 2·5) were enrolled and randomly assigned (150 participants in each group). Day 28 anti-PT IgG seroconversion rates were 141 (94%) of 150 participants who received Tdapgen (95% CI 88·8-97·0) and 105 (71%) of 149 participants who received Tdapchem (62·7-77·2; p<0·0001). Day 28 anti-FHA IgG seroconversion rates were 144 (96%) of 150 participants who received Tdapgen (91·4-98·3) and 124 (83%) of 149 participants who received Tdapchem (76·4-88·4; p<0·0001). The difference in seroconversion rates was 23·5% (95% CI 15·3-31·8) for anti-PT IgG and 12·8% (6·0-19·6) for anti-FHA IgG, when comparing the Tdapgen versus the Tdapchem vaccine group. No vaccine-related serious adverse events were reported.

INTERPRETATION

Recombinant Tdapgen vaccine showed non-inferior immunogenicity compared with Tdapchem at day 28 in terms of seroconversion rate of anti-PT IgG and anti-FHA IgG relative to baseline. The reduced-dose approach for Tdapgen vaccines thus presents as a potentially cost-saving booster strategy to protect adolescents against pertussis.

FUNDING

Office of National Higher Education Science Research and Innovation Policy Council (Programme Management Unit Competitiveness), Thailand, and BioNet-Asia.

Pertussis vaccines, epidemiology and evolution

Pertussis, which is caused by Bordetella pertussis, has plagued humans for at least 800 years, is highly infectious and can be fatal in the unvaccinated, especially very young infants. Although the rollout of whole-cell pertussis (wP) vaccines in the 1940s and 1950s was associated with a drastic drop in incidence, concerns regarding the reactogenicity of wP vaccines led to the development of a new generation of safer, acellular (aP) vaccines that have been adopted mainly in high-income countries. Over the past 20 years, some countries that boast high aP coverage have experienced a resurgence in pertussis, which has led to substantial debate over the basic immunology, epidemiology and evolutionary biology of the bacterium. Controversy surrounds the duration of natural immunity and vaccine-derived immunity, the ability of vaccines to prevent transmission and severe disease, and the impact of evolution on evading vaccine immunity. Resolving these issues is made challenging by incomplete detection of pertussis cases, the absence of a serological marker of immunity, modest sequencing of the bacterial genome and heterogeneity in diagnostic methods of surveillance. In this Review, we lay out the complexities of contemporary pertussis and, where possible, propose a parsimonious explanation for apparently incongruous observations.

Transplacental transfer of maternal antibodies following immunization with recombinant pertussis vaccines during pregnancy: Real-world evidence

AIM/OBJECTIVE

This study investigates placental antibody transfer following recombinant pertussis vaccination in pregnancy in a real-world setting.

METHODS

This postmarketing observational study recruited pregnant women vaccinated with monovalent recombinant acellular pertussis (aP) vaccine (aPgen; n = 199) or combined to tetanus-diphtheria (TdaPgen; n = 200), or Td-vaccine only (n = 54). Pregnancy, delivery, and neonatal outcomes were assessed. Cord blood was collected postdelivery and pertussis toxin (PT)-IgG, filamentous hemagglutinin (FHA)-IgG, and PT-neutralizing antibodies (PT-Nab) were assessed.

RESULTS

No adverse pregnancy, delivery, or neonatal outcomes attributed to aPgen, TdaPgen, or Td vaccination were reported. High anti-PT antibody levels were detected in cord samples from women vaccinated with aPgen (geometric mean concentration [GMC] PT-IgG 206.1 IU/ml, 95% confidence intervals [CI]: 164.3-258.6; geometric mean titer [GMT] PT-Nab 105.3 IU/ml, 95% CI: 81.7-135.8) or TdaPgen (GMC PT-IgG 153.1 IU/ml, 95% CI: 129.1-181.5; GMT PT-Nab 81.5 IU/ml, 95% CI: 66.4-100.0). In the Td-only group, anti-PT antibodies were low (GMC PT-IgG 6.5 IU/ml, 95% CI: 4.9-8.8; GMT PT-Nab 3.8 IU/ml, 95% CI: 2.8-5.1). The same was found for FHA-IgG. Recombinant pertussis vaccination at <27 or 27-36 weeks gestation induced similar cord pertussis antibody levels.

CONCLUSION

This first real-world study confirms that recombinant pertussis vaccination in the second or third trimester of pregnancy results in high levels of passive immunity in infants. Thai Clinical Trial Registry: TCTR20200528006.

Assessing the Impact of the 2020 Council of State and Territorial Epidemiologists Case Definition for Pertussis on Reported Pertussis Cases

BACKGROUND

In 2020, the Council of State and Territorial Epidemiologists (CSTE) pertussis case definition was modified; the main change was classifying polymerase chain reaction (PCR)-positive cases as confirmed, regardless of cough duration. Pertussis data reported through Enhanced Pertussis Surveillance (EPS) in 7 sites and the National Notifiable Diseases Surveillance System (NNDSS) were used to evaluate the impact of the new case definition.

METHODS

We compared the number of EPS cases with cough onset in 2020 to the number that would have been reported based on the prior (2014) CSTE case definition. To assess the impact of the change nationally, the proportion of EPS cases newly reportable under the 2020 CSTE case definition was applied to 2020 NNDSS data to estimate how many additional cases were captured nationally.

RESULTS

Among 442 confirmed and probable cases reported to EPS states in 2020, 42 (9.5%) were newly reportable according to the 2020 case definition. Applying this proportion to the 6124 confirmed and probable cases reported nationally in 2020, we estimated that the new definition added 582 cases. Had the case definition not changed, reported cases in 2020 would have decreased by 70% from 2019; the observed decrease was 67%.

CONCLUSIONS

Despite a substantial decrease in reported pertussis cases in the setting of coronavirus disease 2019 (COVID-19), our data show that the 2020 pertussis case definition change resulted in additional case reporting compared with the previous case definition, providing greater opportunities for public health interventions such as prophylaxis of close contacts.

The durability of vaccine-induced protection: an overview

INTRODUCTION

Current vaccines vary widely in both their efficacy against infection and disease, and the durability of the efficacy. Some vaccines provide practically lifelong protection with a single dose, while others provide only limited protection following annual boosters. What variables make vaccine-induced immune responses last? Can breakthroughs in these factors and technologies help us produce vaccines with better protection and fewer doses? The durability of vaccine-induced protection is now a hot area in vaccinology research, especially after COVID-19 vaccines lost their luster. It has fueled discussion on the eventual utility of existing vaccines to society and bolstered the anti-vaxxer camp. To sustain public trust in vaccines, lasting vaccines must be developed.

AREAS COVERED

This review summarizes licensed vaccines' protection. It analyses immunological principles and vaccine and vaccinee parameters that determine longevity of antibodies. The review concludes with challenges and the way forward to improve vaccine durability.

EXPERT OPINION

Despite enormous advances, we still lack essential markers and reliable correlates of lasting protection. Most research has focused on humoral immune responses, but we must also focus on innate, mucosal, and cellular responses - their assessment, correlates, determinants, and novel adjuvants. Suitable vaccine designs and platforms for durable immunity must be found.

Controlled Human Infection with Bordetella pertussis

Bordetella pertussis, a slow-growing Gram-negative coccobacillus and the causative agent of whooping cough, is one of the leading causes of vaccine-preventable death and morbidity globally. A state of asymptomatic human carriage has not yet been demonstrated by population studies but is likely to be an important reservoir for community transmission of infection. Such a carriage state may be a target for future vaccine strategies. This chapter presents a short summary of the characteristics of B. pertussis, which should be taken into account when developing a human challenge model and any future experimental medicine interventions. Three studies involving deliberate infection with B. pertussis have been described to date. The first of these was a scientifically and ethically unacceptable paediatric challenge study involving four children in 1930. The second was an investigation of a putative live vaccine using a genetically modified and attenuated strain of B. pertussis. Finally, a systematically constructed human challenge model using a wild-type, potentially pathogenic strain has been established. The latter study has demonstrated that deliberate induction of asymptomatic colonisation in humans is safe and immunogenic, with colonised participants exhibiting seroconversion to pertussis antigens. It has also shown nasal wash to be a more sensitive method of detecting the presence of B. pertussis than either pernasal swab or throat swab, and that B. pertussis carriage can be cleared effectively with Azithromycin. The development of this wild-type B. pertussis human challenge model will allow the investigation of host-pathogen and facilitate future vaccine development.

High post-exposure prophylaxis (PEP) uptake among household contacts of pertussis patients enrolled in a PEP effectiveness evaluation - United States, 2015-2017

BACKGROUND

Post-exposure prophylaxis (PEP) for pertussis is recommended for household contacts of pertussis cases in the United States within 21 days of exposure, but data on PEP effectiveness for prevention of secondary cases in the setting of widespread pertussis vaccination are limited. We implemented a multi-state evaluation of azithromycin PEP use and effectiveness among household contacts.

METHODS

Culture- or PCR-confirmed pertussis cases were identified through surveillance. Household contacts were interviewed within 7 days of case report and again 14-21 days later. Interviewers collected information on exposure, demographics, vaccine history, prior pertussis diagnosis, underlying conditions, PEP receipt, pertussis symptoms, and pertussis testing. A subset of household contacts provided nasopharyngeal and blood specimens during interviews.

RESULTS

Of 299 household contacts who completed both interviews, 12 (4%) reported not receiving PEP. There was no evidence of higher prevalence of cough or pertussis symptoms among contacts who did not receive PEP. Of 168 household contacts who provided at least one nasopharyngeal specimen, four (2.4%) were culture or PCR positive for B. pertussis; three of these received PEP prior to their positive test result. Of 156 contacts with serologic results, 14 (9%) had blood specimens that were positive for IgG anti-pertussis toxin (PT) antibodies; all had received PEP.

CONCLUSIONS

Very high PEP uptake was observed among household contacts of pertussis patients. Although the number of contacts who did not receive PEP was small, there was no difference in prevalence of pertussis symptoms or positive laboratory results among these contacts compared with those who did receive PEP.

Novel approaches to reactivate pertussis immunity

INTRODUCTION

Whole cell and acellular pertussis vaccines have been very effective in decreasing the deaths of neonates and infants from Bordetella pertussis. Despite high vaccine coverage worldwide, pertussis remains one of the most common vaccine-preventable diseases, thus suggesting that new pertussis vaccination strategies are needed. Several candidates are currently under development, such as acellular pertussis vaccines that use genetically detoxified pertussis toxin, acellular pertussis vaccines delivered with new adjuvants or new delivery systems, or an intranasally delivered, live attenuated vaccine.

AREAS COVERED

This review discusses the different possibilities for improving current pertussis vaccines and the present state of knowledge on the pertussis vaccine candidates under development.

EXPERT OPINION

Until there is a safe, effective, and affordable alternative to the two types of existing vaccines, we should maintain sufficient childhood coverage and increase the vaccination of pregnant women, adolescents, and young adults.

Lessons from a mature acellular pertussis vaccination program and strategies to overcome suboptimal vaccine effectiveness

INTRODUCTION

Despite high vaccination coverage among children and adolescents, pertussis remains a public health problem, with large outbreaks occurring periodically in the US and other developed countries.

AREAS COVERED

We examine lessons learned more than 20 years after implementation of programs which use only acellular pertussis vaccines and propose avenues for possible effective use of acellular pertussis vaccine to prevent large outbreaks.

EXPERT OPINION

Acellular pertussis vaccines were introduced more than 20 years ago, yet the incidence of pertussis has been increasing over the past decade, with periodic large outbreaks marked by notable shifts in disease burden from infants and young children toward fully vaccinated adolescents and young adults. This age shift is mainly driven by the waning of vaccine immunity. To better protect adolescents against pertussis, modification of the current acellular pertussis vaccination schedule or adoption of new vaccination strategies should be considered. For infants not yet eligible to be vaccinated, maternal vaccination against pertussis during pregnancy is an effective way to protect infants from infection, severe disease and death. Implementation of maternal vaccination programs should be encouraged in countries without one or efforts to improve coverage should be supported in countries with existing program.

Pertussis (Whooping Cough)

Pertussis (whooping cough) is a respiratory infection caused by Bordetella pertussis. All ages are susceptible. In the prevaccine era, almost all children became infected. Pertussis is particularly dangerous in young infants, who account for practically all hospitalizations and deaths, but clinical disease is burdensome at any age. Widespread use of pertussis vaccines dramatically reduced cases, but concern over adverse reactions led to the replacement of standard whole-cell by acellular pertussis vaccines that contain only a few selected pertussis antigens and are far less reactogenic. Routine administration of acellular pertussis vaccines combined with diphtheria and tetanus toxoids is recommended in infancy with toddler and preschool boosters, at age 11, and during pregnancy. Boosting in the second half of every pregancy is critical to protection of the newborn. Waning of vaccine immunity over time has become an increasing concern, and several new pertussis vaccines are being evaluated to address this problem.

Waning immunity after receipt of Pertussis, Diphtheria, Tetanus and Polio-related vaccines: a systematic review and meta-analysis

DTP-containing (pertussis, diphtheria and tetanus) combined with polio vaccines are recommended by WHO as part of routine immunization programs. The decline of immunity after vaccination has been considered as a possible reason for the re-emergence of vaccine-preventable diseases worldwide. In this study, we evaluated the potential duration of protective immunity of pertussis, diphtheria, tetanus and polio through a systematic review and meta-analysis. We examined data on immunological and clinical outcomes. We observed evidence of waning post-vaccination immunity for pertussis and diphtheria, while tetanus and polio vaccines provided sustained protection. Further research on the risk factors of waning immunity after vaccination and the optimal timing of booster doses for pertussis and diphtheria are needed.

Bordetella pertussis in School-Age Children, Adolescents and Adults: A Systematic Review of Epidemiology and Mortality in Europe

Pertussis (whooping cough) epidemics persist globally despite high vaccine coverage among infants and young children. The resurgence of pertussis in high-income countries is partly due to waning vaccine immunity, resulting in a pool of unprotected adolescents and adults. However, pertussis is generally less severe in adolescents and adults, and this difference in presentation means it can often be unrecognised by healthcare professionals, meaning that it is largely under-diagnosed in older populations. A systematic search of MEDLINE, EMBASE and BIOSIS was undertaken to identify studies published between 1 January 1990 and 17 June 2019, with information on pertussis epidemiology and mortality in school-aged children, adolescents and adults in Europe. A formal statistical comparison (e.g. using meta-analyses) was not possible because of the mix of methodologies reported. There were 69 epidemiological studies and 19 mortality studies identified for review. Over the past decade, the reported incidence of notified pertussis cases varied widely between European countries, which is likely associated with differences in surveillance systems, diagnostic techniques and reporting regulations. However, several studies show that pertussis is circulating among adolescents and adults in Europe, and although pertussis-related morbidity and mortality are highest in infants, there is evidence that adults aged > 50 years are at increased risk. For example, in a hospital-based surveillance study in Portugal, between 2000 and 2015, 94% of hospitalised pertussis cases were infants aged < 1 year, with a case fatality rate (CFR) of 0.8%; however, among hospitalised adult cases of pertussis, the CFRs were 11.5% (aged 18–64 years) and 17.4% (aged > 65 years). Very few European countries currently include pertussis boosters for adults in the national immunisation strategy. In addition to increasing pertussis vaccination coverage in adolescents and adults, mitigation strategies in European countries should include improved diagnosis and treatment in these populations.

Pertussis vaccine effectiveness and duration of protection - A systematic review and meta-analysis

A comprehensive review of observational pertussis vaccine effectiveness (VE) studies is needed to update gaps from previous reviews. We conducted a systematic review of VE and duration of protection studies for the whole-cell (wP) and acellular (aP) pertussis vaccines and conducted a formal meta-analysis using random effects models. Evidence continues to suggest that receipt of any pertussis vaccine confers protection in the short-term against disease although this protection wanes rapidly for aP vaccine. We detected significant heterogeneity in pooled estimates due, in part, to factors such as bias and confounding which may be mitigated by study design. Our review of possible sources of heterogeneity may help interpretation of other VE studies and aid design decisions in future pertussis VE research.

Optimizing Immunization Strategies in Patients with IBD

Recent advances in the treatment of inflammatory bowel disease (IBD) include the use of immune modifiers and monoclonal antibodies, such as tumor necrosis factor (TNF) alpha inhibitors, anti-integrin agents, janus kinase inhibitors, and interleukin-12/23 inhibitors. These agents achieve higher rates of clinical remission and mucosal healing than conventional therapy. However, these therapies increase the risk of infections, including some vaccine-preventable diseases. Infections are one of the most common adverse event of immunosuppressive therapy. Thus, providers should optimize immunization strategies to reduce the risk of vaccine-preventable infections in patients with IBD. There are several newly licensed vaccines recommended for adults by the US Advisory Committee on Immunization Practices. This review will focus on how gastroenterology providers can implement the adult immunization schedule approved by ACIP for patients with IBD.

Immunological Distinctions between Acellular and Whole-Cell Pertussis Immunizations of Baboons Persist for at Least One Year after Acellular Vaccine Boosting

While both whole-cell (wP) and acellular pertussis (aP) vaccines have been highly effective at reducing the global pertussis disease burden, there are concerns that compared to wP vaccination, the immune responses to aP vaccination may wane more rapidly. To gain insights into the vaccine elicited immune responses, pre-adult baboons were immunized with either aP or wP vaccines, boosted with an aP vaccine, and observed over a nearly two-year period. Priming with a wP vaccine elicited a more Th17-biased response than priming with aP, whereas priming with an aP vaccine led to a more Th2-biased response than priming with wP. These differences were maintained after aP vaccine boost immunizations. Compared to aP, animals primed with a wP vaccine exhibited greater numbers of pertussis specific memory B cells. While aP and wP vaccine priming initially elicited similar levels of anti-pertussis toxin antibody, titers declined more rapidly in aP vaccine primed animals leading to a 4-fold difference. Both wP and aP vaccine immunization could induce serum bactericidal activity (SBA); however, only one wP vaccine immunization was required to elicit SBA while multiple aP vaccine immunizations were required to elicit lower, less durable SBA titers. In conclusion, when compared to aP vaccine, priming with wP vaccine elicits distinct cellular and humoral immune responses that persist after aP vaccine boosting.

Efficacy, safety, and formulation issues of the combined vaccines

Introduction: Controlling the preventable infectious diseases is the main goal of vaccination. Among the vaccines, combined vaccines are of great importance for their social, public health, and economic values. It is stated that the combined vaccines are as efficient and safe as the monovalent vaccines. However, a concern has raised about the efficacy and safety of the combined vaccines due to the outbreaks of vaccine-preventable diseases and occurrence of serious adverse events. Areas covered: A retrospective literature search was conducted in the Google Scholar and PubMed databases to evaluate the efficacy and safety of the combined vaccines from 1980 to 2020 using appropriate keywords. Expert opinion: Several studies have shown efficacy and safety issues related to the combined vaccines. Different factors contribute to the inefficacy and lack of safety in the vaccines including formulation problems, limited data in the pre-licensure studies and challenges related to imperfection of the post-licensure surveillance systems. For surmounting the mentioned obstacles, there is a need to provide new formulations of the vaccines, revise the vaccines҆ safety and efficacy acceptance standards in the pre-licensure studies, improvement of post-licensure surveillance systems, and education of healthcare staff.

Safety and immunogenicity of the epicutaneous reactivation of pertussis toxin immunity in healthy adults: a phase I, randomized, double-blind, placebo-controlled trial

OBJECTIVES

Protection induced by acellular vaccines can be short, requiring novel immunization strategies. Objectives of this study were to evaluate safety and capacity of a recombinant pertussis toxin (PTgen) -coated Viaskin® epicutaneous patch to recall memory responses in healthy adults.

METHODS

This double-blind, placebo-controlled randomized trial (Phase I) assessed the safety and immunogenicity of PTgen administered on days 0 and 14 to healthy adults using Viaskin® patches applied directly or after epidermal laser-based skin preparation. Patch administration was followed by Boostrix®dTpa on day 42. Antibodies were assessed at days 0, 14, 28, 42 and 70.

RESULTS

Among 102 volunteers enrolled, 80 received Viaskin-PT (Viaskin-PT 25 μg (n = 25), Viaskin-PT 50 μg (n = 25), laser + Viaskin-PT 25 μg (n = 5), laser + Viaskin-PT 50 μg (n = 25)), Viaskin-placebo (n = 10) or laser + Viaskin-placebo (n = 2). Incidence of adverse events was similar across groups (any local event: 21/25 (84.0%), 24/25 (96.0%), 4/5 (80.0%), 24/25 (96.0%), 8/10 (80.0%), 10/12 (83.0%), respectively). Direct application induced no detectable response. On day 42, PT-IgG geometric mean concentrations were significantly higher following laser + Viaskin-PT 25 μg and 50 μg (139.87 (95% CI 87.30-224.10) and 121.76 (95% CI 95.04-156.00), respectively), than laser + Viaskin-placebo (59.49, 95% CI 39.37-89.90). Seroresponse rates were higher following laser + Viaskin-PT 25 μg (4/5 (80.0%), 95% CI 28.4-99.5) and 50 μg (22/25 (88.0%), 95% CI 68.8-97.5) than laser + Viaskin-placebo (0/12 (0.0%), 95% CI 0.0-26.5).

CONCLUSIONS

Viaskin-PT applied after laser-based epidermal skin preparation showed encouraging safety and immunogenicity results: anti-PT booster responses were not inferior to those elicited by Boostrix®dTpa. This study is registered at ClinicalTrials.gov (NCT03035370) and was funded by DBV Technologies.

Vaccine-Preventable Infections in Childcare Workers

BACKGROUND

Adequate immunity to so-called childhood diseases can lower the occupational risk of vaccine-preventable infectious diseases in persons who work in day-care centers for children.

METHODS

A systematic literature survey was carried out in PubMed and Embase for the period January 2000 to February 2019. Studies on immune status and vaccination status were included. In addition, data from the first wave of the German Health Interview and Examination Survey for Adults (Studie zur Gesundheit Erwachsener in Deutschland, DEGS1) and surveillance data on notifiable infections in Germany were evaluated.

RESULTS

Six studies and the DEGS1 analysis of vaccination or immune status for varicella zoster, rubella, hepatitis A (HAV), pertussis, measles, and mumps in persons caring for children in day-care centers, most of whom are women, were included in this review. According to DEGS1, childcare workers are more commonly vaccinated against HAV and pertussis than the general female population (prevalence ratios [PR]: 1.46 [1.12; 1.90] and 1.57 [1.05; 2.36]), yet 57% had not been vaccinated against HAV and 77% had not been vaccinated against pertussis. Childcare workers were found to be less commonly vaccinated against rubella than the general female population, although the difference was not statistically significant (PR: 0.87 [0.71; 1.07]). In a Canadian study, positive HAV serology was found to be correlated with the duration of activity as a childcare worker. In the DEGS1 study, large proportions of the younger childcare workers in particular were seronegative against measles (16%), mumps (19%), and HAV (37%). Notifiable disease statistics show that those working in community facilities had a markedly higher risk of mumps, pertussis, and varicella (relative risk [RR]: 1.8-2.6) and a somewhat higher risk of rubella and HAV (RR: 1.47 and 1.21, respectively).

CONCLUSION

Childcare workers have a higher occupational risk of infection but do not always receive the appropriate vaccinations. In particular, women of child-bearing age working in day-care centers should be made more aware of the need for vaccination.

Boosting Teenagers With Acellular Pertussis Vaccines Containing Recombinant or Chemically Inactivated Pertussis Toxin: A Randomized Clinical Trial

BACKGROUND

Protection induced by acellular pertussis (aP) vaccines is partial and short-lived, especially in teenagers, calling for novel immunization strategies.

METHODS

We conducted an investigator-driven proof-of-concept randomized controlled trial in aP-primed adolescents in Geneva to assess the immunogenicity and reactogenicity of a novel recombinant aP (r-aP) vaccine including recombinant pertussis toxin (PT) and filamentous hemagglutinin (FHA) coadministered with tetanus-diphtheria toxoids (Td), compared to a licensed tetanus-diphtheria-aP vaccine containing chemically detoxified PT (cd/Tdap). The primary immunological endpoints were day 28/365 geometric mean concentrations (GMCs) of total and neutralizing anti-PT antibodies. Memory B cells were assessed.

RESULTS

Sixty-two aP-primed adolescents were randomized and vaccinated with r-aP + Td or cd/Tdap. Reactogenicity, adverse events, and baseline GMCs were similar between the groups. Day 28 PT-neutralizing GMCs were low after cd/Tdap (73.91 [95% confidence interval {CI}, 49.88-109.52] IU/mL) and approximately 2-fold higher after r-aP + Td (127.68 [95% CI, 96.73-168.53] IU/mL; P = .0162). Anti-PT GMCs were also low after cd/Tdap (52.43 [95% CI, 36.41-75.50] IU/mL) and 2-fold higher after r-aP + Td (113.74 [95% CI, 88.31-146.50] IU/mL; P = .0006). Day 28 anti-FHA GMCs were similar in both groups. Day 365 anti-PT (but not PT-neutralizing) GMCs remained higher in r-aP + Td vaccinees. PT-specific memory B cells increased significantly after r-aP + Td but not cd/Tdap boosting.

CONCLUSIONS

Boosting aP-primed adolescents with r-aP induced higher anti-PT and PT-neutralizing responses than cd/Tdap and increased PT-specific memory B cells. Despite this superior immunogenicity, r-aP may have to be given repeatedly, earlier, and/or with novel adjuvants to exert an optimal influence in aP-primed subjects.

CLINICAL TRIALS REGISTRATION

NCT02946190.

A qPCR assay for Bordetella pertussis cells that enumerates both live and dead bacteria

Bordetella pertussis is the causative agent of whooping cough, commonly referred to as pertussis. Although the incidence of pertussis was reduced through vaccination, during the last thirty years it has returned to high levels in a number of countries. This resurgence has been linked to the switch from the use of whole-cell to acellular vaccines. Protection afforded by acellular vaccines appears to be short-lived compared to that afforded by whole cell vaccines. In order to inform future vaccine improvement by identifying immune correlates of protection, a human challenge model of B. pertussis colonisation has been developed. Accurate measurement of colonisation status in this model has required development of a qPCR-based assay to enumerate B. pertussis in samples that distinguishes between viable and dead bacteria. Here we report the development of this assay and its performance in the quantification of B. pertussis from human challenge model samples. This assay has future utility in diagnostic labs and in research where a quantitative measure of both B. pertussis number and viability is required.

Tetanus, diphtheria and acellular pertussis (Tdap) vaccine for prevention of pertussis among adults aged 19 years and older in the United States: A cost-effectiveness analysis

Currently, the Advisory Committee on Immunization Practices recommends one-time tetanus toxoid, reduced diphtheria toxoid, and acellular pertussis (Tdap) vaccination for all adults 19 years and older. This study is designed to evaluate the cost-effectiveness of Tdap vaccination for Tdap-eligible adults aged 19 through 85 in the United States. A cost-effectiveness model was developed to compute costs and health outcomes associated with pertussis among 100,000 Tdap-eligible persons of each age cohort. From the societal perspective, the cost per quality-adjusted life-year (QALY) saved was evaluated under the vaccination scenarios. Sensitivity analyses were also conducted to evaluate the impacts of changes in key variables. All costs were adjusted to 2018 US$ with an annual discount rate of 3% applied to costs and outcomes. The incremental cost-effectiveness ratios (ICERs) for vaccinating US adults aged 19 to 85 with Tdap ranged from $248,000/QALY to $900,000/QALY. The lowest cost per QALY was found to be $248,000 for the age 65 cohort, followed by $332,000 for the cohort of age 19, and followed by $477,000 for the age 50 cohort. Sensitivity analysis showed the most dramatic changes in ICER occurred when changing the underreporting factor, vaccine effectiveness and vaccination costs. While Tdap vaccination may not be as cost effective as predicted earlier, it remains the best available preventive measure against pertussis. Further investigation of the true burden of pertussis disease among adults and the effectiveness of Tdap vaccination in this population is needed to better estimate the impact of Tdap vaccination.

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).

Successful Vaccines

Vaccines are considered one of the most important advances in modern medicine and have greatly improved our quality of life by reducing or eliminating many serious infectious diseases. Successful vaccines have been developed against many of the most common human pathogens, and this success has not been dependent upon any one specific class of vaccine since subunit vaccines, non-replicating whole-virus or whole-bacteria vaccines, and attenuated live vaccines have all been effective for particular vaccine targets. After completing the initial immunization series, one common aspect of successful vaccines is that they induce long-term protective immunity. In contrast, several partially successful vaccines appear to induce protection that is relatively short-lived and it is likely that long-term protective immunity will be critical for making effective vaccines against our most challenging diseases such as AIDS and malaria.

The 112-Year Odyssey of Pertussis and Pertussis Vaccines-Mistakes Made and Implications for the Future

Effective diphtheria, tetanus toxoids, whole-cell pertussis (DTwP) vaccines became available in the 1930s, and they were put into routine use in the United States in the 1940s. Their use reduced the average rate of reported pertussis cases from 157 in 100 000 in the prevaccine era to <1 in 100 000 in the 1970s. Because of alleged reactions (encephalopathy and death), several countries discontinued (Sweden) or markedly decreased (United Kingdom, Germany, Japan) use of the vaccine. During the 20th century, Bordetella pertussis was studied extensively in animal model systems, and many "toxins" and protective antigens were described. A leader in B pertussis research was Margaret Pittman of the National Institutes of Health/US Food and Drug Administration. She published 2 articles suggesting that pertussis was a pertussis toxin (PT)-mediated disease. Dr Pittman's views led to the idea that less-reactogenic acellular vaccines could be produced. The first diphtheria, tetanus, pertussis (DTaP) vaccines were developed in Japan and put into routine use there. Afterward, DTaP vaccines were developed in the Western world, and definitive efficacy trials were carried out in the 1990s. These vaccines were all less reactogenic than DTwP vaccines, and despite the fact that their efficacy was less than that of DTwP vaccines, they were approved in the United States and many other countries. DTaP vaccines replaced DTwP vaccines in the United States in 1997. In the last 13 years, major pertussis epidemics have occurred in the United States, and numerous studies have shown the deficiencies of DTaP vaccines, including the small number of antigens that the vaccines contain and the type of cellular immune response that they elicit. The type of cellular response a predominantly, T2 response results in less efficacy and shorter duration of protection. Because of the small number of antigens (3-5 in DTaP vaccines vs >3000 in DTwP vaccines), linked-epitope suppression occurs. Because of linked-epitope suppression, all children who were primed by DTaP vaccines will be more susceptible to pertussis throughout their lifetimes, and there is no easy way to decrease this increased lifetime susceptibility.

Effectiveness of Acellular Pertussis Vaccine in Older Adults: Nested Matched Case-control Study

Background

Despite recommendations that older adults receive acellular pertussis vaccines, data on direct effectiveness in adults aged over 50 years are sparse.

Methods

A case-control study nested within an adult cohort. Cases were identified from linked pertussis notifications and each matched to 3 controls on age, sex, and cohort recruitment date. Cases and controls were invited to complete a questionnaire, with verification of vaccination status by their primary care provider. Vaccine effectiveness (VE) was estimated by conditional logistic regression, with adjustment for reported contact with children and area of residence.

Results

Of 1112 notified cases in the cohort, we had complete data for 333 cases and 506 controls. Among 172 PCR-diagnosed cases (mean age, 61 years), 11.2% versus 19.5% of controls had provider-verified pertussis vaccination, on average, 3.2 years earlier. Adjusted VE against PCR-diagnosed pertussis was 52% (95% CI, 15–73%), nonsignificantly higher if vaccinated within 2 years (63%; −5–87%). Adjusted VE was similar in adults born before 1950, presumed primed by natural infection (51%; −8–77%) versus those born 1950 or later who may have received whole-cell pertussis vaccine (53%; −11–80%) (P-heterogeneity = 0.9). Among 156 cases identified by single-point serology, adjusted VE was −55% (−177–13%).

Conclusions

We found modest protection against PCR-confirmed pertussis among older adults (mean age, 61 years; range, 46–81 years) within 5 years after acellular vaccine. The most likely explanation for the markedly divergent VE estimate from cases identified by single-titer serology is misclassification arising from limited diagnostic specificity in our setting.

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.

On the role of different age groups during pertussis epidemics in California, 2010 and 2014

There is limited information on the roles of different age groups in propagating pertussis outbreaks, and the temporal changes in those roles since the introduction of acellular pertussis vaccines. The relative roles of different age groups in propagating the 2010 and the 2014 pertussis epidemics in California were evaluated using the relative risk (RR) statistic that measures the change in the group's proportion among all detected cases before vs. after the epidemic peak. For the 2010–11 epidemic, evidence for a predominant transmission age group was weak, with the largest RR estimates being 1.26 (95% CI 1.08–1.46) (aged 11–13 years); 1.19 (1.01–1.4) (aged 9–10 years); 1.17 (0.86–1.59) (aged 14–15 years); 1.12 (0.86–1.46) (aged 16–19 years) and 1.1 (0.89–1.36) (aged 7–8 years). The 2014 epidemic showed a strong signal of the role of older adolescents, with the highest RR estimate being in those aged 14–15 years (RR = 1.83, 1.61–2.07), followed by adolescents aged 16–19 years (RR = 1.41, 1.24–1.61) and 11–13 years (RR = 1.26, 1.12–1.41), with lower RR estimates in other age groups. As the time following introduction of acellular pertussis vaccines in California progressed, older adolescents played an increasing role in transmission during the major pertussis outbreaks. Booster pertussis vaccination for older adolescents with vaccines effective against pertussis transmission should be considered with the aim of mitigating future pertussis epidemics in the community.

Awareness, Knowledge, and Coverage of Vaccination Against Tetanus, Diphtheria, and Pertussis Among Medical Students of Karachi: A Cross-sectional Analysis

Background Along with reducing the global burden of diphtheria, pertussis and tetanus, the DPT3 (diphtheria-pertussis-tetanus) vaccine protects health care professionals (HCPs) as well as vulnerable patients in their care. This study evaluates awareness, knowledge and coverage of DPT3 vaccine and boosters among medical students of public university in Karachi, Pakistan. Methods A cross-sectional study consisting of 281 participants selected through convenience sampling was conducted from July 2017 to July 2018 using a self-administered questionnaire. Results While 93% participants received childhood doses of DPT3, only 39.2% received adult boosters. Students with positive immunization history in childhood and family vaccination routines were more likely to get adult boosters. Eighty-six percent of the students were unaware that their university had a recommended vaccination program as a part of the admission process. The assessment of awareness and knowledge revealed that only 10.5% individuals could be regarded as well-aware, 20.3% (n = 58) students as unaware, and 69.2% (n = 198) participants as moderately aware. Conclusion The level of awareness, knowledge and coverage of DPT3 vaccine is insufficient among medical students of a public university of Karachi; universities are recommended to take measures to enhance knowledge and ensure strict adherence of students to appropriate vaccination programs.

Human Immune Responses to Pertussis Vaccines

Pertussis still represents a major cause of morbidity and mortality worldwide. Although vaccination is the most powerful tool in preventing pertussis and despite nearly 70 years of universal childhood vaccination, incidence of the disease has been rising in the last two decades in countries with high vaccination coverage. Two types of vaccines are commercially available against pertussis: whole-cell pertussis vaccines (wPVs) introduced in the 1940s and still in use especially in low and middle-income countries; less reactogenic acellular pertussis vaccines (aPVs), licensed since the mid-1990s.In the last years, studies on pertussis vaccination have highlighted significant gaps and major differences between the two types of vaccines in the induction of protective anti-pertussis immunity in humans. This chapter will discuss the responses of the immune system to wPVs and aPVs, with the aim to enlighten critical points needing further efforts to reach a good level of protection in vaccinated individuals.

Recommendations to control pertussis prioritized relative to economies: A Global Pertussis Initiative update

Pertussis is a vaccine-preventable disease that causes morbidity and mortality, particularly in infants and children <5 years of age. The Global Pertussis Initiative (GPI) recommendations represent a systematic evaluation and prioritization of strategies to prevent pertussis-related infant and child deaths, reduce global disease burden and prevent resurgence through vaccination strategies and public health policies at national, regional and local levels. The GPI recommendations are based on clinical trials and observational and surveillance data, which are essential in the planning, implementation and evaluation of vaccination practices and best use of available resources. Many low- and middle-income countries (LMIC) continue to use whole-cell pertussis (wP) vaccines for primary vaccination, while most high-income countries have replaced wP with the less-reactogenic acellular pertussis (aP) vaccines. This present manuscript pertains to discussions held during the GPI's meeting on November 11-13, 2016, in Cape Town, Republic of South Africa. The GPI recommends that LMIC aim for high coverage of infant series pertussis vaccines as a priority. In LMIC and countries with constrained vaccine funding, if wP vaccines are currently used, wP should continue to be used. Furthermore, given that protection against disease and death due to pertussis in neonates is a key priority of the GPI, it recommends that ap immunization in pregnancy should be implemented as a priority in all countries if resources allow. Given that surveillance and epidemiology data on which to base vaccine decisions are important, the GPI also suggests that, in areas where wP vaccines are implemented, standardization and calibration of wP vaccines are checked, considering the many different manufacturers and variable standards of production and quality control. In addition, as immunity to pertussis wanes following the primary infant series of vaccination, the GPI further recommends that toddlers, adolescents, healthcare and childcare workers receive booster vaccine doses, where resources allow.

Antibody persistence after vaccination of adolescents with monovalent and combined acellular pertussis vaccines containing genetically inactivated pertussis toxin: a phase 2/3 randomised, controlled, non-inferiority trial

BACKGROUND

The immunogenicity of acellular pertussis vaccines and persistence of immunity after vaccination might be improved by using genetically inactivated pertussis toxin (PTgen) instead of chemically inactivated pertussis toxin (PTchem) because of the preservation of conformational epitopes. We assessed the safety and immunogenicity of two vaccines containing PTgen 1 year after vaccination.

METHODS

We did a phase 2/3 non-inferiority, randomised, controlled trial involving 450 adolescents (age 12-17 years) enrolled between July 6, 2015, and Aug 20, 2015. Participants were randomised 1:1:1 to receive one dose of vaccine containing PTgen and filamentous haemagglutinin (FHA) either in a monovalent formulation (aP_[PTgen/FHA]) or in a combined formulation with tetanus and reduced-dose diphtheria toxoids (TdaP_[PTgen/FHA]) or to receive a commercial vaccine containing reduced-dose PTchem (Tdap) as a comparator. We report a secondary trial outcome, namely antibody persistence 1 year after vaccination, assessed per protocol in 150 randomly preselected participants (50 per group). Seroconversion was defined as antibody titres at least four times greater than at baseline. Safety was assessed in all trial participants. This study is registered in the Thai Clinical Trial Registry, number TCTR20150703002.

FINDINGS

Between June 5, 2016, and Aug 9, 2016, 442 (98%) of 450 enrolled participants attended a 1-year follow-up visit. After 1 year, persistent seroconversion for pertussis toxin neutralising antibodies was seen in 38 (76%, 95% CI 64-88) participants in the aP_(PTgen/FHA) group and 41 (81%, 70-92) in the TdaP_(PTgen/FHA) group, but in only four (8%, 1-16) in the Tdap comparator group. Seroconversion rates for IgG antibodies against pertussis toxin and FHA were also greater in the aP_(PTgen/FHA) group (82%, 95% CI 71-93 and 64%, 51-77, respectively) and TdaP_(PTgen/FHA) group (75%, 63-87 and 56%, 42-70, respectively) than in the Tdap group (4%, 0-9, p<0·0001, and 28%, 16-41, p=0·0007, respectively). 13 serious adverse events were reported in 12 participants and all were judged to be unrelated to the study vaccines. Five pregnancies were reported during follow-up, none of which had any maternal or neonatal complications.

INTERPRETATION

A monovalent and a combined recombinant acellular pertussis vaccine containing PTgen induced antibody responses that were greater and sustained for longer than those achieved with the Tdap comparator vaccine. New recombinant pertussis vaccines containing PTgen might offer new opportunities to limit pertussis resurgence and can be widely used, including in pregnant women.

FUNDING

BioNet-Asia.

On the Role of Different Age Groups and Pertussis Vaccines During the 2012 Outbreak in Wisconsin

Background

There is limited information on the roles of different age groups in propagating pertussis outbreaks, and on the impact of vaccination on pertussis transmission in the community.

Methods

The relative roles of different age groups in propagating the 2012 pertussis outbreak in Wisconsin were evaluated using the relative risk (RR) statistic that measures the change in the group’s proportion among all detected cases before vs after the epidemic peak. The impact of vaccination in different age groups against infection (that is potentially different from the protective effect against detectable disease) was evaluated using the odds ratios (ORs), within each age group, for being vaccinated vs undervaccinated before vs after the outbreak’s peak.

Results

The RR statistic suggests that children aged 13–14 years played the largest relative role during the outbreak’s ascent (with estimates consistent across the 3 regions in Wisconsin that were studied), followed by children aged 7–8, 9–10, and 11–12 years. Young children and older teenagers and adults played more limited relative roles during the outbreak. Results of the vaccination status analysis for the fifth dose of DTaP (for children aged 7–8 years: OR, 0.44; 95% confidence interval [CI], 0.23–0.86; for children aged 9–10 years: OR, 0.51; 95% CI, 0.27–0.95); and for Tdap for children aged 13–14 years (OR, 0.38, 95% CI, 0.16–0.89) are consistent with protective effect against infection.

Conclusions

While our epidemiological findings for the fifth dose of DTaP and for Tdap are consistent with protective effect against infection, further studies, including those estimating vaccine effectiveness against infection/transmission to others particularly for pertussis vaccines for adolescents, are needed to evaluate the impact of vaccination on the spread of pertussis in the community.

Acellular pertussis vaccines effectiveness over time: A systematic review, meta-analysis and modeling study

Background

Acellular pertussis vaccine studies postulate that waning protection, particularly after the adolescent booster, is a major contributor to the increasing US pertussis incidence. However, these studies reported relative (ie, vs a population given prior doses of pertussis vaccine), not absolute (ie, vs a pertussis vaccine naïve population) efficacy following the adolescent booster. We aim to estimate the absolute protection offered by acellular pertussis vaccines.

Methods

We conducted a systematic review of acellular pertussis vaccine effectiveness (VE) publications. Studies had to comply with the US schedule, evaluate clinical outcomes, and report VE over discrete time points. VE after the 5-dose childhood series and after the adolescent sixth-dose booster were extracted separately and pooled. All relative VE estimates were transformed to absolute estimates. VE waning was estimated using meta-regression modeling.

Findings

Three studies reported VE after the childhood series and four after the adolescent booster. All booster studies reported relative VE (vs acellular pertussis vaccine-primed population). We estimate initial childhood series absolute VE is 91% (95% CI: 87% to 95%) and declines at 9.6% annually. Initial relative VE after adolescent boosting is 70% (95% CI: 54% to 86%) and declines at 45.3% annually. Initial absolute VE after adolescent boosting is 85% (95% CI: 84% to 86%) and declines at 11.7% (95% CI: 11.1% to 12.3%) annually.

Interpretation

Acellular pertussis vaccine efficacy is initially high and wanes over time. Observational VE studies of boosting failed to recognize that they were measuring relative, not absolute, VE and the absolute VE in the boosted population is better than appreciated.

Safety of repeated doses of tetanus toxoid, reduced diphtheria toxoid, and acellular pertussis vaccine in adults and adolescents

In light of waning immunity to pertussis following receipt of tetanus toxoid, reduced diphtheria toxoid and acellular pertussis (Tdap) vaccine, maintaining protection may require repeated Tdap vaccination. We evaluated the safety of repeated doses of tetanus-containing vaccine in 68 915 nonpregnant adolescents and adults in the Vaccine Safety Datalink population who had received an initial dose of Tdap. Compared with 7521 subjects who received a subsequent dose of tetanus toxoid, reduced diphtheria (Td) vaccine, the 61 394 subjects who received a subsequent dose of Tdap did not have significantly elevated risk of medical visits for seizure, cranial nerve disorders, limb swelling, pain in limb, cellulitis, paralytic syndromes, or encephalopathy/encephalitis/meningitis. These results suggest that repeated Tdap vaccination has acceptable safety relative to Tdap vaccination followed by Td vaccination.

Assessment of Tdap Vaccination Effectiveness in Adolescents in Integrated Health-Care Systems

PURPOSE

Despite high national vaccination coverage with tetanus toxoid, reduced diphtheria toxoid, and acellular pertussis (Tdap) vaccines among U.S. adolescents, rates of adolescent pertussis disease are increasing. We estimated the duration of protection after Tdap vaccination and the possible effects of the change from whole-cell to acellular childhood pertussis vaccines in the United States during the 1990s.

METHODS

We conducted a retrospective cohort analysis among 11- to 18-year-olds enrolled in two integrated health-care delivery systems during 2005-2012. Cases met the Council of State and Territorial Epidemiologists' confirmed or probable definition or a polymerase chain reaction-positive suspect definition. We estimated vaccine effectiveness (VE) overall and by time since Tdap receipt. We stratified VE estimates by primary series pertussis vaccine received (based on birth year): mixed-vaccine cohort (1987-1997) and acellular vaccine cohort (1998-2001).

RESULTS

The overall Tdap VE was 57% (95% confidence interval [CI]: 42%-68%); the VE in the mixed-vaccine and acellular cohorts was 65% (95% CI: 44%-78%) and 52% (95% CI: 30%-68%), respectively. Tdap VE within <2 years post vaccination (69%, 95% CI: 54%-79%) was significantly different from VE ≥2 years post vaccination (34%, 95% CI: 1%-55%, p value < .01). VE was significantly higher <2 years post vaccination compared with ≥2 years post vaccination in both mixed-vaccine (87%, 95% CI: 58%-96%, and 52%, 95% CI: 13%-73%; p value = .04) and acellular cohorts (62%, 95% CI: 41%-76%, and 21%, 95% CI: -30% to 52%; p value = .01).

CONCLUSIONS

Although Tdap vaccination remains the best pertussis prevention method for adolescents, protection wanes within 2 years regardless of the type of childhood primary vaccine. Vaccines with longer duration of protection could decrease pertussis burden.

Lower Sustained Diphtheria and Pertussis Antibody Concentrations in Inflammatory Bowel Disease Patients

BACKGROUND

Patients with inflammatory bowel disease (IBD) are often immunosuppressed, and those patients receiving anti-tumor necrosis factor α (TNF) therapy can have lower antibody responses to vaccines. Pertussis cases are at their highest levels in the post-vaccine era. There is little data regarding responses to the Tdap (tetanus, diphtheria, and acellular pertussis) vaccine in IBD patients.

AIMS

The aim of this study was to compare sustained vaccine-induced Tdap antibody concentrations in a cohort of IBD patients stratified by medication regimens with healthy controls (HC) who had received an adult Tdap booster.

METHODS

We performed a cross-sectional study evaluating antibody responses to Tdap vaccine among IBD patients compared to HC. Our study consisted of three patient groups: adults with IBD stratified by maintenance medication regimen: (1) thiopurine monotherapy; (2) anti-TNF monotherapy; and (3) combination therapy (anti-TNF and immunomodulator (thiopurine or methotrexate)).

RESULTS

Ninety IBD patients and 20 HC participated. Pertussis pertactin antibody concentrations were significantly lower in IBD patients (p = 0.021) compared to HC, and those on anti-TNF agents (monotherapy or combination) had lower antibody concentrations compared to those on thiopurine monotherapy (p = 0.028). Diphtheria antibody concentrations were also lower in IBD patients (p < 0.001), and those on anti-TNF agents (monotherapy or combination) had lower antibody concentrations compared to the thiopurine monotherapy group (p < 0.001).

CONCLUSION

IBD patients on anti-TNF agents had lower antibody concentrations to diphtheria and pertussis. These findings suggest a need for different Tdap booster schedules for IBD patients on anti-TNF therapy. Clinical Trials Registry NCT02434133.

Reduced Severity of Pertussis in Persons With Age-Appropriate Pertussis Vaccination-United States, 2010-2012

Background

In 2012, >48000 pertussis cases were reported in the United States. Many cases occurred in vaccinated persons, showing that pertussis vaccination does not prevent all pertussis cases. However, pertussis vaccination may have an impact on disease severity.

Methods

We analyzed data on probable and confirmed pertussis cases reported through Enhanced Pertussis Surveillance (Emerging Infections Program Network) between 2010 and 2012. Surveillance data were collected through physician and patient interview and vaccine registries. We assessed whether having received an age-appropriate number of pertussis vaccines (AAV) (for persons aged ≥3 months) was associated with reduced odds of posttussive vomiting, a marker of more clinically significant illness, or of severe pertussis (seizure, encephalopathy, pneumonia, and/or hospitalization). Adjusted odds ratios were calculated using multivariable logistic regression.

Results

Among 9801 pertussis patients aged ≥3 months, 77.6% were AAV. AAV status was associated with a 60% reduction in odds of severe disease in children aged 7 months-6 years in multivariable logistic regression and a 30% reduction in odds of posttussive vomiting in persons aged 19 months-64 years.

Conclusions

Serious pertussis symptoms and complications are less common among AAV pertussis patients, demonstrating that the positive impact of pertussis vaccination extends beyond decreasing risk of disease.

Immunogenicity and safety of a second booster dose of an acellular pertussis vaccine combined with reduced antigen content diphtheria-tetanus toxoids 10 years after a first booster in adolescence: An open, phase III, non-randomized, multi-center study

Pertussis is a highly contagious disease, for which periodic peaks in incidence and an increasing number of outbreaks have been observed over the last decades. The reduced-antigen-content tetanus-diphtheria-acellular pertussis vaccine (Tdap) can be used to boost individuals aged ≥10 years, vaccinated in infancy with a diphtheria-tetanus-acellular pertussis vaccine (DTaP), to reduce pertussis morbidity and maintain protection against diphtheria and tetanus throughout adolescence and adulthood. This phase III, open-label, non-randomized, multicenter follow-up study (NCT01738477) enrolled 19–30-year-old participants from the United States who had received booster vaccination 10 years earlier with either Tdap (Tdap group) or Td (Td group). In total, 128 (Tdap group) and 37 (Td group) participants received Tdap vaccination. After administration of Tdap, all participants were seroprotected (antibody concentrations ≥0.1 international units [IU]/ml) against diphtheria and tetanus. Immune responses to a second Tdap dose in the Tdap group were shown to be non-inferior to responses elicited by a first Tdap dose in the Td group for diphtheria and tetanus and to a 3-dose DTaP vaccination during infancy for pertussis antigens (primary objectives). Post-booster vaccination, all participants in both groups had antibody concentrations above assay cut-offs and antibody geometric mean concentrations increased by 3.8–15.5-fold compared to pre-booster levels for all antigens. The incidence of adverse events was similar in the Td (80.6%) and Tdap (85.6%) groups (no serious adverse events reported). A Tdap dose administered after previous Td or Tdap vaccination was shown to be immunogenic and well-tolerated in young adults, supporting repeated vaccination with Tdap at 10-year intervals.

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.

Detection and incidence of Bordetella holmesii in respiratory specimens from patients with pertussis-like symptoms in New South Wales, Australia

Bordetella pertussis, the aetiological agent of whooping cough is routinely diagnosed by polymerase chain reaction (PCR) directed at IS481, an insertion sequence target also found in Bordetella holmesii. Recent reports have suggested that B. holmesii infections can be misdiagnosed as pertussis, which can have a significant impact on public health surveillance. This study investigated the presence of B. holmesii in B. pertussis positive clinical samples, in order to determine the incidence of B. holmesii. Clinical cases of pertussis diagnosed by IS481-specific PCR between October 2008 and March 2016 in New South Wales were included. Bordetella holmesii was detected through the simultaneous amplification of IS481 and B. holmesii specific insertions sequence, hIS1001. A total of 46 of 802 patients were identified to be positive for B. holmesii rather than B. pertussis, suggesting an incidence rate of 6.5% in 2009, 16.8% in 2010, 7.6% during 2013 and 8.1% during 2015. Bordetella holmesii infections were diagnosed during and between pertussis epidemics, however cases of B. holmesii and B. pertussis co-infections were not found. The predominant age group of B. holmesii infection was 11-18 years old, which was significantly different to the mean age of B. pertussis infections (0-6 years, p = 0.023). These findings revealed that B. holmesii was co-circulating alongside the B. pertussis epidemic for seven years, hidden from view, as B. holmesii infections have been diagnosed as B. pertussis. Confirmatory testing of B. pertussis positive samples for the presence of B. holmesii, especially during pertussis epidemics, should improve the quality of laboratory diagnosis and laboratory surveillance for pertussis. The presence of B. holmesii in Australia highlights the importance of testing for this pathogen and ongoing molecular surveillance that can guide the control of whooping cough.

An Assessment of the Cocooning Strategy for Preventing Infant Pertussis-United States, 2011

BACKGROUND

 Infants are at greatest risk for severe pertussis. In 2006, the Advisory Committee on Immunization Practices recommended that adolescents and adults, especially those with infant contact, receive a single dose of Tdap (tetanus toxoid, reduced diphtheria toxoid, and acellular pertussis vaccine). To assess the effectiveness of cocooning, we conducted a case-control evaluation of infant close contacts.

METHODS

 Pertussis cases aged <2 months with onset between 1 January 2011 and 31 December 2011 were identified in Emerging Infections Program Network sites. For each case, we recruited 3 controls from birth certificates and interviewed identified adult close contacts (CCs) or parents of CCs aged <18 years. Pertussis vaccination was verified through medical providers and/or immunization registries.

RESULTS

 Forty-two cases were enrolled, with 154 matched controls. Around enrolled infants, 859 CCs were identified (600 adult and 259 nonadult). An average of 5.4 CCs was identified per case and 4.1 CCs per control. Five hundred fifty-four (64.5%) CCs were enrolled (371 adult and 183 non-adult CCs); 119 (32.1% of enrolled) adult CCs had received Tdap. The proportion of Tdap-vaccinated adult CCs was similar between cases and controls (P = .89). The 600 identified adult CCs comprised 172 potential cocoons; 71 (41.3%) potential cocoons had all identified adult CCs enrolled. Of these, 9 were fully vaccinated and 43.7% contained no Tdap-vaccinated adults. The proportion of fully vaccinated case (4.8%) and control (10.0%) cocoons was similar (P = .43).

CONCLUSIONS

 Low Tdap coverage among adult CCs reinforces the difficulty of implementing the cocooning strategy and the importance of vaccination during pregnancy to prevent infant pertussis.

What Is Wrong with Pertussis Vaccine Immunity? Why Immunological Memory to Pertussis Is Failing

Memory responses seen after whole-cell pertussis (wP) and acellular pertussis (aP) vaccine priming are different and reflect better long-term protection against pertussis disease seen with the whole-cell vaccines. Although acellular vaccines generate higher levels of antigen-specific IgG to the antigens included in the aP vaccines, there are many more pertussis antigens included in whole-cell vaccines. Acellular vaccine priming is associated with skewing of the immune response to a more Th2-like response, whereas whole-cell priming is associated with a Th1/Th17 response. Repeated booster doses of acellular vaccine in children primed with acellular vaccine has been shown to result in progressively shorter duration of protection against disease. This may be explained by the generation of higher levels of antigen-specific IgG4, which does not bind complement and leads to a suboptimal inflammatory response and impaired phagocytosis and antimicrobial defense. In contrast, whole-cell priming followed by aP vaccine boosters results in better opsonization, phagocytosis, and complement mediated killing through the preferential induction of IgG1.

What Is Wrong with Pertussis Vaccine Immunity? Inducing and Recalling Vaccine-Specific Immunity

The high incidence of pertussis in vaccinated adolescents suggests the failing of immune memory. We argue that acellular pertussis vaccines generate memory cells that are effectively reactivated by boosters better than by Bordetella pertussis exposure. We propose that there are two main causes. One is the induction of vaccine-specific immunity rather than pathogen-specific immunity. The second is that strictly mucosal infections such as B. pertussis poorly reactivate memory B and T cells residing deep in lymph nodes or tissues. Developing new vaccines for infants or adolescents will be immunologically and economically challenging. Let us hope that maternal and infant immunization, to date the most effective strategies against pertussis death, will remain so.