Gayatri Amirthalingam

Effectiveness of maternal pertussis vaccination in England: an observational study

BACKGROUND In October, 2012, a pertussis vaccination programme for pregnant women was introduced in response to an outbreak across England. We aimed to assess the vaccine effectiveness and the overall effect of the vaccine programme in preventing pertussis in infants. METHODS We undertook an analysis of laboratory-confirmed cases and hospital admissions for pertussis in infants between Jan 1, 2008, and Sept 30, 2013, using data submitted to Public Health England as part of its enhanced surveillance of pertussis in England, to investigate the effect of the vaccination programme. We calculated vaccine effectiveness by comparing vaccination status for mothers in confirmed cases with estimates of vaccine coverage for the national population of pregnant women, based on data from the Clinical Practice Research Datalink. FINDINGS The monthly total of confirmed cases peaked in October, 2012 (1565 cases), and subsequently fell across all age groups. For the first 9 months of 2013 compared with the same period in 2012, the greatest proportionate fall in confirmed cases (328 cases in 2012 vs 72 cases in 2013, -78%, 95% CI -72 to -83) and in hospitalisation admissions (440 admissions in 2012 vs 140 admissions in 2013, -68%, -61 to -74) occurred in infants younger than 3 months, although the incidence remained highest in this age group. Infants younger than 3 months were also the only age group in which there were fewer cases in 2013 than in 2011 (118 cases in 2011 vs 72 cases in 2013), before the resurgence. 26?684 women included in the Clinical Practice Research Datalink had a livebirth between Oct 1, 2012 and Sept 3, 2013; the average vaccine coverage before delivery based on this cohort was 64%. Vaccine effectiveness based on 82 confirmed cases in infants born from Oct 1, 2012, and younger than 3 months at onset was 91% (95% CI 84 to 95). Vaccine effectiveness was 90% (95% CI 82 to 95) when the analysis was restricted to cases in children younger than 2 months. INTERPRETATION Our assessment of the programme of pertussis vaccination in pregnancy in England is consistent with high vaccine effectiveness. This effectiveness probably results from protection of infants by both passive antibodies and reduced maternal exposure, and will provide valuable information to international policy makers. FUNDING Public Health England.

A case-control study to estimate the effectiveness of maternal pertussis vaccination in protecting newborn infants in England and Wales, 2012-2013

BACKGROUND Infants with pertussis infection are at risk of severe clinical illness and death. Several countries, including the United Kingdom, have introduced maternal pertussis vaccination during pregnancy to protect infants from infection following national increases in pertussis notifications. The objective of this study was to estimate the effectiveness of maternal pertussis vaccination in protecting infants against laboratory-confirmed pertussis infection. METHODS A case-control study was undertaken in England and Wales between October 2012 and July 2013. Cases were infants aged <8 weeks at onset with pertussis infection tested by real-time polymerase chain reaction or culture. Family doctors of each case were asked to identify healthy infants born consecutively after the case in each practice, to act as controls. Fifty-eight cases and 55 controls were included in this study. Odds ratios (ORs) were calculated for the association between maternal vaccination and infant pertussis infection. The vaccine effectiveness (VE) was calculated as 1 - OR. This was adjusted for sex, geographical region, and birth period. RESULTS Mothers of 10 cases (17%) and 39 controls (71%) received pertussis vaccine in pregnancy. This gave an unadjusted VE of 91% (95% confidence interval [CI], 77%-97%). Adjusted VE was 93% (95% CI, 81%-97%). CONCLUSIONS Maternal pertussis vaccination is effective in preventing pertussis infection in infants aged <8 weeks and may be considered in other countries experiencing high levels of pertussis notifications.

Antibody Responses After Primary Immunization in Infants Born to Women Receiving a Pertussis-containing Vaccine During Pregnancy: Single Arm Observational Study With a Historical Comparator

INTRODUCTION In England, antenatal pertussis immunization using a tetanus/low-dose diphtheria/5-component acellular-pertussis/inactivated-polio (TdaP5/IPV) vaccine was introduced in October 2012. We assessed infant responses to antigens in the maternal vaccine and to those conjugated to tetanus (TT) or the diphtheria toxin variant, CRM. METHODS Infants of 141 TdaP5/IPV-vaccinated mothers in Southern England immunized with DTaP5/IPV/Haemophilus influenzae b (Hib-TT) vaccine at 2-3-4 months, 13-valent pneumococcal vaccine (PCV13, CRM-conjugated) at 2-4 months and 1 or 2 meningococcal C vaccine (MCC-CRM- or MCC-TT) doses at 3-4 months had blood samples taken at 2 and/or 5 months of age. RESULTS Antibody responses to pertussis toxin (PT), filamentous hemagglutinin (FHA), fimbriae 2 + 3 (FIMs), diphtheria, tetanus, Hib, MCC and PCV13 serotypes were compared to responses in a historical cohort of 246 infants born to mothers not vaccinated in pregnancy. Infants had high pertussis antibody concentrations pre-immunization but only PT antibodies increased post-immunization (fold-change, 2.64; 95% confidence interval [CI], 2.12-3.30; P < .001), whereas FHA antibodies fell (fold-change, 0.56; 95% CI, .48-.65; P < .001). Compared with infants of unvaccinated mothers, PT, FHA, and FIMs antibodies were lower post-vaccination, with fold-differences of 0.67 (0.58-0.77; P < .001), 0.62 (0.54-0.71; P < .001) and 0.51 (0.42-0.62; P < .001), respectively. Antibodies to diphtheria and some CRM-conjugated antigens were also lower, although most infants achieved protective thresholds; antibodies to tetanus and Hib were higher. CONCLUSIONS Antenatal pertussis immunization results in high infant pre-immunization antibody concentrations, but blunts subsequent responses to pertussis vaccine and some CRM-conjugated antigens. In countries with no pertussis booster until school age, continued monitoring of protection against pertussis is essential.

Pertussis immunisation and control in England and Wales, 1957 to 2012: a historical review.

This review summarises the epidemiology and control of pertussis in England and Wales since the introduction of routine immunisation and considers the implications for future control. Routine infant immunisation with a whole-cell pertussis (wP) vaccine was introduced in 1957 and had a marked impact on the overall disease burden. Following a fall in vaccine coverage during the 1970s and 80s linked to a safety scare with wP vaccine, there was an extended period of high coverage and pertussis incidence fell dramatically. Incidence continued to decrease with the introduction of an acellular pertussis vaccine in the pre-school booster in November 2001 and in the primary United Kingdom (UK) schedule in September 2004 but has increased since July 2011. In response to a high rate of pertussis in infants, a temporary vaccination programme for pregnant women was introduced in October 2012. The key aim of the programme is to protect vulnerable infants from birth in the first months of life, before they can be fully protected by routine infant immunisation. A review of the UK adolescent immunisation programme is currently ongoing and the inclusion of a pertussis booster is being considered.

Accelerating control of pertussis in England and Wales.

Pertussis incidence among infants can be reduced by early completion of the primary vaccination schedule.

Strategies to control pertussis in infants

The UK is currently in the midst of a large outbreak of pertussis, with the highest morbidity and mortality occurring in young unimmunised infants. This review considers the potential strategies to optimise control of pertussis in infants, including vaccination of (1) adolescents, (2) close household contacts of newborn infants (cocooning), (3) newborn infants and (4) pregnant women. The paper discusses the evidence base for each of these strategies and considers the rationale for the recent introduction of a temporary vaccination programme for pregnant women in the UK in response to the ongoing outbreak.

Sustained Effectiveness of the Maternal Pertussis Immunization Program in England 3 Years Following Introduction

The effectiveness of maternal immunization in preventing infant pertussis was first demonstrated in England, 1 year after the program using diphtheria–tetanus–5-component acellular pertussis–inactivated polio vaccine (dT5aP-IPV) was introduced in 2012. Vaccine effectiveness against laboratory-confirmed pertussis has been sustained >90% in the 3 years following its introduction, despite changing to another acellular vaccine with different antigen composition. Consistent with this, disease incidence in infants <3 months of age has remained low despite high activity persisting in those aged 1 year and older. Vaccine effectiveness against infant deaths was estimated at 95% (95% confidence interval, 79%–100%). Additional protection from maternal immunization is retained in infants who received their first dose of the primary series. There is no longer evidence of additional protection from maternal vaccination after the third infant dose. Although numbers are small and ongoing assessment is required, there is no evidence of increased risk of disease after primary immunization in infants whose mothers received maternal vaccination.

The Social Life of Infants in the Context of Infectious Disease Transmission; Social Contacts and Mixing Patterns of the Very Young

Insight into how humans interact helps further understanding of the transmission of infectious diseases. For diseases such as pertussis, infants are at particular risk for severe outcomes. To understand the contact pattern of infants, especially those too young to be vaccinated, we sent contact diaries to a representative sample of 1000 mothers in the United Kingdom. We received 115 responses with a total of 758 recorded contacts. The average number of daily contacts for an infant was 6.68 overall and 5.7 for those aged ≤10 weeks. Of the latter, 2.1 (37%) contacts were with non-household members and were >15 minutes duration, suggesting that a cocooning programme may miss a substantial proportion of exposures leading to disease transmission. The least contact was between adolescents and infants. Thus the impact of adolescent (pertussis) vaccination on infants would likely be limited, unless it reduces transmission to other age groups whose contact with infants is greater.

Whooping cough in school age children presenting with persistent cough in UK primary care after introduction of the preschool pertussis booster vaccination: prospective cohort study.

Objective To estimate the prevalence and clinical severity of whooping cough (pertussis) in school age children presenting with persistent cough in primary care since the introduction and implementation of the preschool pertussis booster vaccination. Design Prospective cohort study (November 2010 to December 2012). Setting General practices in Thames Valley, UK. Participants 279 children aged 5 to 15 years who presented in primary care with a persistent cough of two to eight weeks’ duration. Exclusion criteria were cough likely to be caused by a serious underlying medical condition, known immunodeficiency or immunocompromise, participation in another clinical research study, and preschool pertussis booster vaccination received less than one year previously. Main outcome measures Evidence of recent pertussis infection based on an oral fluid anti-pertussis toxin IgG titre of at least 70 arbitrary units. Cough frequency was measured in six children with laboratory confirmed pertussis. Results 56 (20%, 95% confidence interval 16% to 25%) children had evidence of recent pertussis infection, including 39 (18%, 13% to 24%) of 215 children who had been fully vaccinated. The risk of pertussis was more than three times higher (21/53; 40%, 26% to 54%) in children who had received the preschool pertussis booster vaccination seven years or more previously than in those who had received it less than seven years previously (20/171; 12%, 7% to 17%). The risk of pertussis was similar between children who received five and three component preschool pertussis booster vaccines (risk ratio for five component vaccine 1.14, 0.64 to 2.03). Four of six children in whom cough frequency was measured coughed more than 400 times in 24 hours. Conclusions Pertussis can still be found in a fifth of school age children who present in primary care with persistent cough and can cause clinically significant cough in fully vaccinated children. These findings will help to inform consideration of the need for an adolescent pertussis booster vaccination in the United Kingdom. Study registration UK Clinical Research Network portfolio ID 8361.

Maternal vaccination against pertussis: a systematic review of the recent literature

Objective This study is conducted to summarise and present the current knowledge on antenatal vaccination against pertussis with regard to national recommendations, coverage, immunogenicity, safety and effectiveness of the current available vaccines. Methods A systematic review of the literature in English was undertaken from January 2011 to May 2016 with searches in four databases. The review conformed to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Results 47 studies fulfilled the inclusion criteria. Antenatal vaccination against pertussis induces high antibody concentrations in pregnant women, which are efficiently transferred transplacentally to the fetus and protect newborns when they are most vulnerable to pertussis. This strategy has been demonstrated to be safe, with no evidence of adverse pregnancy, birth or neonatal outcomes. Several countries have already introduced antenatal pertussis vaccination into their national immunisation programme with varying vaccination coverage influenced by various factors. Barriers to achieving high immunisation rates could be improved through better education of the public and healthcare professionals. Conclusions There is now an increasing body of evidence to support the safety, immunogenicity and effectiveness of antenatal vaccination to reduce the morbidity and mortality associated with pertussis in neonates and young infants before they receive their primary immunisations. Narrowing the gap between scientific evidence and public health policies is critical in order to protect the most vulnerable as quickly as possible. The lessons learnt have important implications for implementation of new vaccines into the antenatal immunisation programme.