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TITLE: Maternal vaccination against pertussis: a systematic review of the
recent literature
Author names and affiliations.
Despoina Gkentzi1,2, Paraskevi Katsakiori3, Markos Marangos2, Yingfen Hsia4,
Gayatri Amirthalingam5, Paul Heath4, Shamez Ladhani4,5
1Department of Paediatrics, University General Hospital of Patras, Rio, Greece2Department of Infectious Diseases, Patras Medical School, Rio, Greece3Department of General Practice, Health Centre of Akrata, Akrata, Greece4Paediatric Infectious Diseases Research Group, & Vaccine Institute, Institute of Infection &
Immunity, St. Georges, University of London, UK5 Immunisation, Hepatitis and Blood Safety Department, Public Health England, London, UK
Corresponding author:
Despoina Gkentzi, Department of Paediatrics, University General Hospital of Patras, Patras
Medical School, Rio, Greece
E-mail: [email protected],
Telephone number: 0030 6972307569,
Fax number: 0030 2610994683
Word Count: 3392
Keywords
Maternal vaccination, pertussis, safety, immunogenicity, effectiveness, pregnancy
1
ABSTRACT
Objective: 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 PRISMA
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 foetus 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.
2
MAIN TEXT
INTRODUCTION
Bordetella pertussis continues to circulate and cause major epidemics both in the developed
and the developing world despite the widespread use of pertussis vaccines. In 2008, WHO
estimated that 16 million cases of pertussis occurred worldwide, with 95% of cases occurring
in developing countries, and nearly 200,000 children dying from the disease.1 In 2013,
pertussis was still causing around 63 000 deaths in children aged < 5 years,2 whereas in 2015
WHO reported 142,512 cases of pertussis worldwide.3 Changes in the circulating organism
strains, improved diagnostic methods, waning of both vaccine and natural immunity as well
as decreased effectiveness of the acellular compared to the whole cell vaccine have been
proposed to explain the continuing circulation of B. pertussis. Adults and adolescents are
considered to be the main and persistent transmitters of pertussis in the community, but the
highest morbidity and mortality is among the young infants. In particular, the majority of
severe pertussis cases, hospitalisations, intensive care admissions and deaths occur in infants
younger than two months (i.e. prior to receiving their primary immunisations).4, 5 Proposed
strategies to decrease pertussis disease burden in this vulnerable group include adolescent
vaccination, cocooning, antenatal and neonatal vaccination.6, 7 Neonatal vaccination
inevitably leaves the infant at risk until they have responded to the first or subsequent doses,8-
10 while cocooning relies on vaccination of everyone likely to have contact with the newborn
with the aim of preventing infection in adults in order to reduce transmission to the infant and
is difficult to implement.11 Maternal vaccination, on the other hand, not only protects the
pregnant woman but also offers passive immunity to the newborn via transplacental transport
of maternal antibodies and is currently considered as the most successful and effective
intervention to prevent infant disease.6, 12
3
In view of the public health importance of pertussis particularly in young infants, the
importance of maternal vaccination in reducing disease burden and the recent pertussis
epidemics during the last five years, we undertook this review to systematically summarise
and present the recently published data on maternal vaccination against pertussis with regard
to national recommendations, coverage, immunogenicity, safety and effectiveness of the
current available vaccines.
METHODS
Review methods and eligibility criteria
This review was conducted in accordance with PRISMA guidelines.13 We reviewed all
published literature in the English language on maternal vaccination against pertussis in
humans from January 2011 to May 2016. All publications were eligible for review, with
particular emphasis on observational and interventional studies. The high volume of reviews
already published in the field was also assessed for their context and references. They were
included in the present systematic review only if they contained original results or had
exceptional content.
Information sources
The search was conducted in the MEDLINE, EMBASE, Scopus, and Cochrane library. The
last search was performed on the 31 May 2016. We used the following key words and
combinations of these words for the search: pertussis, pregnan*, vaccin*, maternal,
antenatal and immunisation/immunization. References within included articles were further
reviewed for additional articles. Duplicate publications were identified and removed.
We identified 670 potentially relevant studies through database searches (Figure 1). Of these,
there were 309 duplicates and 314 were excluded on basis of title and abstract screening. The
4
grey literature and national reports were not eligible for inclusion. We, therefore, included 47.
The majority of included studies were from the United States (US) and the United Kingdom
(UK).
RESULTS
Recommendations for antenatal immunisation against pertussis
In 2011, the Advisory Committee on Immunization Practices (ACIP) of the Center for
Disease Control and Prevention (CDC) in the US recommended the combined tetanus toxoid,
reduced diphtheria toxoid and acellular pertussis vaccine (Tdap) vaccination in the third
trimester of pregnancy (between 27 and 36 weeks of pregnancy) for women that had never
received a Tdap vaccine prior to pregnancy.14 This recommendation was modified in 2012 to
include all women, regardless of prior receipt of Tdap and with every pregnancy, following
evidence of waning vaccine immunity after vaccination in the first trimester of pregnancy or
in a previous pregnancy.15
In the UK, following the national outbreak of pertussis in 2012, a temporary antenatal
vaccination programme began in October 2012, offering Tdap to pregnant women, ideally at
28-32 weeks and up to delivery.16-18 In July 2014, the UK Joint Committee on Vaccination
and Immunisation (JCVI) recommended that this programme should continue for at least five
more years, owing to continuing high levels of pertussis activity.19 In April 2016, the UK’s
Department of Health, following JCVI recommendation,20 and reassuring evidence of a Swiss
study,21 of adequate immunogenicity earlier on in pregnancy, updated its advice to
recommend antenatal vaccination at any time between 16-32 weeks of pregnancy,17 in order
to provide greater opportunity for pregnant women to access the vaccine, improve protection
5
for premature babies and increase vaccine-induced antibody levels at birth. Moreover,
women may be vaccinated after week 32 recognising though that this does not offer optimal
passive protection to the baby. However, if it is not possible to immunise earlier, then
vaccinating later in pregnancy is still advisable because it will directly protect pregnant
women against disease, thereby reducing the risk of subsequent exposure to their offspring,
and will also provide some protection to the newborn.
In addition to the US and the UK, antenatal vaccination against pertussis is recommended and
government-funded in a variety of countries worldwide 22, 23 including Argentina,24 Belgium,25
Brazil,22 Colombia,22 El-Salvador,22 Mexico,22 New Zealand,26 Australia,27 Switzerland,28
Ireland,29 Czech Republic,29 Israel,30 Spain,31 and Greece.32
Immunogenicity and Interference
Transplacental transfer of vaccine-induced antibodies from the mother to the foetus before
birth and through breastfeeding after birth is the rationale behind antenatal
immunisation.33The immunogenicity of pertussis-containing vaccines has been studied in
various studies where almost a thousand women were vaccinated in pregnancy and compared
to unvaccinated pregnant women (Table 1). These studies have shown high rates of passive
antibody transfer from the mother to the foetus prior to delivery. In one randomised trial, the
33 pregnant women who received Tdap at 30-32 weeks gestation and their infants had higher
pertussis antibodies at delivery compared to the 15 women who received the vaccine
postpartum and their infants.34 In another randomised controlled trial on pneumococcal
vaccination schedules, higher pertussis antibody concentrations prior to routine infant
immunisation at two months of age were reported in 31 premature infants whose mothers had
received Tdap at 28-32 weeks gestation, compared to premature infants of unvaccinated
6
mothers.35 Other studies have also reported high concentrations and high antibody avidity of
vaccine-induced antibodies in infants of mothers receiving Tdap in the third trimester.25, 36-40
A Spanish study reported a high correlation between maternal and infant pertussis toxin (PT)
antibody concentrations following Tdap vaccination at ≥20 weeks’ gestation.41 With regards
to the timing of maternal vaccination, a prospective Australian study reported higher pertussis
antibody concentrations in the cord blood of infants born to women immunised at 28-32
weeks gestation compared to those vaccinated at 33-36 weeks gestation, suggesting that
vaccination early in the third trimester may be more effective than later in pregnancy.40 More
recently, a Swiss study found that early second-trimester maternal Tdap immunisation
(between 13-25 weeks) was associated with significantly higher neonatal pertussis antibody
concentrations compared to vaccination after 26 weeks gestation.21
Maternally-derived antibodies are known to interfere with infant responses to primary
immunisation with the same vaccine antigens.42 Immune interference has also been observed
after immunisation with DTaP vaccines at birth.43 This phenomenon is defined as “blunting”
of vaccine responses.6 Following the introduction of antenatal pertussis vaccination in
October 2012, 141 infants in England were followed up with pre- and post-immunisation
blood tests at two and five months, respectively. This study found higher pertussis antibodies
at two months compared to a historical cohort of 246 infants born to unvaccinated mothers.
However, only PT antibodies increased post-immunisation at five months of age, whereas
filamentous haemagglutinin (FHA) antibodies fell. Moreover, at five months, post-
vaccination antibodies were significantly lower for all pertussis antigens compared with
infants of unvaccinated mothers. There was also evidence of immune interference between
maternal-derived diphtheria and tetanus antibodies induced by the maternal Tdap/IPV
vaccine and infant responses to some of the tetanus toxoid- and CRM-carrier protein
conjugated vaccines.44 In a randomised controlled trial conducted in Vietnam pregnant
7
women received either a Tdap vaccine or a tetanus only vaccine between 19 and 35 weeks'
gestational age.45 Significantly higher geometric mean concentrations (GMC) were observed
for all three measured pertussis antigens i.e. PT, FHA and pertactin (PRN) in the offspring of
the Tdap group, up to two months of age. One month after completion of the primary infant
vaccination schedule, anti-PRN GMC, but not anti-PT and anti-FHA GMCs, was
significantly higher in the control group.
In a recently published prospective cohort from Belgium, blunting was observed for PT
antibody responses following the third dose of the primary immunisation schedule in infants
of women receiving a pertussis-containing vaccine in pregnancy compared to those of
unvaccinated women.25 After the booster dose of vaccine, anti-PT IgG concentrations in the
former group of infants remained significantly lower, while antibody concentrations for the
other pertussis antigens increased.46 These findings are slightly different and less reassuring
than those reported in the randomised control trial by Munoz et al.34 In this study, after
primary immunisation, infants of women who received Tdap during pregnancy achieved
equivalent antibody concentrations against PRN, lower but not statistically significant
antibodies concentrations against PT and FIM, and significantly lower antibody
concentrations against FHA compared to infants whose mothers received placebo. One month
after the booster dose, however, antibody concentrations against all pertussis antigens were
not significantly different in the two groups.34 These findings are similar to those of a
prospective observational study where the marginally lower antibody concentrations after the
primary immunisation series did not persist following the booster.39 These differences could
be explained by differences in the timing of booster DTaP, vaccine brands or population
demographics. Currently, the clinical significance of blunting and antibody waning is not
clear (particularly because of a lack of an established correlate of protection for pertussis),
and their impact on disease is likely to depend on country-specific immunisation schedules.
8
In the UK, for example, the pertussis booster is not offered until the pre-school vaccinations
at three years and four months and, therefore, blunting is more of a concern compared to
countries that boost in the second year of life. Ongoing surveillance in older, vaccinated
infants and toddlers will be critical to understand the longer-term impact and significance of
these immunological findings.
9
Table 1: Studies on Immunogenicity of Maternal Tetanus, Diphtheria, acellular Pertussis (Tdap) vaccine (n=14)
Country
(study years)
Type of study Number of participants-
(vaccine product)
Main findings Reference
USA(2008-2012)
RandomisedControlled Trial
33 women vaccinated in pregnancy with Tdap (Adacel ® Sanofi Pasteur) versus 15 received placebo – Their infants received DTaP vaccine (Pentacel® Sanofi Pasteur)
High concentrations of pertussis antibodies in infants of vaccinated mothers during the first 2 months of life; no significant impact on infant responses to DTaP one month after the booster dose
Munoz et al, 2014
Spain(2012-2013)
Prospective observational
132 women vaccinated in pregnancy (Triaxis Sanofi Pasteur ), and their newborns
Anti-PT antibodies >10 IU/ml in 90.2% of post vaccination maternal samples and 94.7% of newborn samples. At 2 months of age, 66% of newborns had estimated anti-PT levels ≥10 IU/ml.
Vilajeliu et al, 2014
Israel
(2013-2014)
Prospective 53 women vaccinated in
pregnancy (Boostrix GSK)
versus 8 unvaccinated
Higher relative avidity index of umbilical cord IgG to PT in infants born to vaccinated
women versus unvaccinated - higher relative avidity index in those vaccinated at 27-30
weeks of gestation compared to after 31 weeks of gestation
Abu Raya et al,
2015
Israel
(2013-2014)
Prospective 61 women vaccinated in
pregnancy (Boostrix GSK),
between 23 and 38 weeks
gestation (3 at 23–26+6, 51 at
27–36 and 7 at >36 weeks)
GMCs of IgG to PT were higher in cord sera when women immunized at 27-30 (+6)
weeks compared with 31-36 weeks and >36 weeks
Abu Raya et al,
2014
US
(2008-2009)
Prospective
observational
52 women vaccinated in
pregnancy (Sanofi Pasteur
product) and their offspring
versus 52 unimmunised
Higher concentrations of antibodies to PT, FHA, PRN, and FIM 2 & 3 in newborns of
immunised women
Gall et al, 2011
US
(2006-2009)
Prospective
observational
16 women vaccinated in
pregnancy (Adacel ® Sanofi
Pasteur) versus 54
unvaccinated as control group-
At 2 months of age (before the first infant vaccination), pertussis antibody GMCs in
infants of vaccinated mothers were higher than controls. Following the primary series,
antibody concentrations to pertussis antigens were modestly lower in the Tdap group
Hardy-Fairbanks et
al, 2013
10
Their infants received DTaP
vaccine (Pediarix, Pentacel or
Infanrix)
except for FIM which was greater. Antibody concentrations before and after the
booster dose of DTaP at 12–18 months of life showed no notable differences between
groups.
Israel
(2013-2014)
Cohort study 25 women vaccinated women
in pregnancy (Boostrix GSK),
versus 12 unvaccinated
Pertussis specific IgG and IgA antibodies showed a statistically significant decline at 2
weeks postpartum but pertussis IgA antibodies were still present in the breast milk of
the vaccinated women at 8 weeks postpartum
Abu Raya et al,
2014
Sweden
(2014)
Prospective
observational
non-inferiority
non-randomized
controlled study
122 women vaccinated in
pregnancy ((Boostrix GSK) in
the 2nd -trimester (GW 13–25)
versus 213 in the 3rd -trimester
(≥ GW 26)
Early 2nd -trimester Tdap immunisation significantly increased neonatal antibodies
(anti- PT, anti-FHA)
Eberhardt et al, 2016
UK
(2012-2014)
Prospective 31 premature infants of Tdap
(Repevax) vaccinated mothers
in pregnancy compared to 121
premature infants of
unvaccinated mothers
Anti- PT, anti-FHA and anti-FIM 2 & 3 at 2 months were higher in infants of Tdap
vaccinated mothers
Kent et al,2016
UK
(2012-2014)
Prospective 141 children born to women
who received TdaP/IPV
(Repevax) in pregnancy
compared to an historical
cohort of 246 infants born to
unvaccinated mothers .
Infants received DTaP-IPV-Hib
(Pediacel, Sanofi Pasteur)
At 2 months, prior to receiving their primary immunizations, antibody concentrations
to the 3 tested pertussis antigens (PT, FIM, FHA) were high. Compared with the
historical cohort of infants whose mothers did not receive Repevax in pregnancy,
antibody concentrations after primary immunization were lower for all 3 pertussis
antigens
Ladhani et al, 2015
Australia
(2014)
Prospective 154 pregnant women - 3
groups: 53 vaccinated between
28-42 weeks, 62 vaccinated
Cord blood levels higher in vaccinated groups versus non vaccinated - earlier gestation
vaccination group had higher antibody levels than later gestation group
Naidu et al, 2016
11
between 33-36 weeks and 39
non vaccinated. Participants
received Tdap vaccine
containing 8 mg PT, 8 mg
FHA, and 2.5 mg PRN.
Vietnam
(2012-2014)
Randomised
Controlled
51 infants of women vaccinated
with Tdap (Adacel) versus 48
infants of mothers vaccinated
with tetanus vaccine only in
pregnancy. Infants received
Infanrix hexa®(GSK).
Significantly higher GMCs were observed for all 3 measured pertussis antigens in the
offspring of the Tdap group, up to 2 months of age. One month after completion of the
primary infant vaccination schedule, anti-PRN GMC, but not anti-PT and anti-FHA
GMCs, was significantly (p = 0.006) higher in the control group.
Hoang et al, 2016
Belgium
(2012-2014)
Prospective
controlled
57 women vaccinated in
pregnancy (Boostrix,GSK)
versus 42 control non
vaccinated. Their infants
received Infanrix hexa®(GSK)
Infants born to vaccinated women had significantly higher GMC at birth and during
the first 2 months of life for all vaccine antigens compared to the offspring of
unvaccinated women. Blunting was noticed for PT vaccine responses in the infants
from vaccinated women after the primary vaccination schedule .Infants of vaccinated
women had after the booster dose of pertussis- containing vaccine at 15 months lower
anti-PT whereas a rise in all the other antibody titers of pertussis was observed.
Maertens et al,
June 2016
Maertnes et al,
January 2016
GMC: geometric mean concentration, PT: pertussis toxin, FHA: filamentous haemaglutinin, PRN: pertactin, FIM: fimbriae
12
Determinants of Tdap vaccine uptake and strategies to increase uptake
In the US, following the recommendations for antenatal pertussis vaccination, there
has been a general trend towards higher vaccine uptake, although vaccine coverage in
pregnant women is still considered to be low.47-50 Factors associated with lower
vaccine uptake include young maternal age, absence of public insurance, black race
and premature delivery.48, 51, 52 In Mexico, a cross sectional survey found that
recommendation of vaccination by an obstetrician was a strong determinant of
vaccine uptake, whereas the most popular reason for refusal was concern about
vaccine safety.53 Korean women of childbearing age appeared not to be adequately
informed by health care providers (HCPs) about the vaccinations recommended in
pregnancy.54 In a recent UK survey involving 1,013 women of childbearing age,
multiparous women were more likely to accept antenatal vaccinations including
pertussis and to participate in vaccine trials during pregnancy compared to
primiparous.55 In addition, HCPs in the UK were the most important and valuable
source of information for pregnant women.55 Similarly, in Australia, new mothers
were more likely to be vaccinated if they had heard of the disease and the benefits of
vaccination from a HCP.56 In Germany, migration status was associated with lower
vaccine uptake in pregnant women.57
A number of strategies to increase uptake have been proposed, such as electronic
antenatal alerts reminding HCPs to vaccinate pregnant women under their care from
32 weeks gestation and at each subsequent encounter up to delivery until vaccination
is performed and recorded.58 Vaccine coverage using such a best-practice alert
increased from 48% to 97% and this intervention nearly halved the incidence of
neonatal pertussis, although the reduction was not significant, possibly because of
13
small numbers of cases.58 In other studies, mobile phone text alert messages have been
successfully used to improve antenatal care provision in Africa, including maternal
vaccination uptake.59 In Ohio, US, the implementation of a hospital-based outpatient
pertussis prevention clinic improved Tdap vaccination rates in pregnant women and
family members (cocooning strategy).60
A questionnaire-based study involving 133 obstetric providers in New York State
found that, although 92% of them were aware of the national recommendations for
antenatal Tdap vaccination, only 67% provided vaccine in their office. Moreover,
11% and 13% of them expressed concern about vaccine safety and efficacy,
respectively, despite the growing body of literature against these beliefs.61 Concerns
raised included vaccine price, the need to vaccinate in each pregnancy, vaccine safety,
and low incidence of pertussis in the area. The authors concluded that educational
programs were needed to improve provider vaccine confidence and recommendation.
A recent review highlighted the difficulties, relating mainly to financial barriers, in
achieving high antenatal pertussis vaccination coverage in the US (such as the cost of
ordering and storing vaccines, maintaining vaccine inventory, and mainly inadequate
reimbursement) compared to the UK, where antenatal care and vaccination is
provided mainly by general practitioners in primary care.62
In summary, in order to achieve high vaccination coverage in countries with national
recommendations for antenatal vaccination better education of the public and
healthcare providers is essential as well as overcoming financial and logistical
barriers.
14
Safety
During the time frame of this systematic review, no excess in adverse events over
background rates was demonstrated among 138,277 pregnancies assessed (Table 2).
In the UK, following the introduction of antenatal pertussis vaccination in 2012, an
observational study of more than 20,000 pregnant women found no evidence of an
increased risk of stillbirth in the 14 days after vaccination (incidence rate ratio 0·69,
95% CI, 0·23-1·62) or later in pregnancy compared with historical national rates.
There was also no association with any of a wide range of maternal, perinatal and
neonatal outcomes assessed.63
Equally reassuring are the findings of other well-designed observational studies,50, 51,
64-66 including a US retrospective observational cohort study using data from two
California Vaccine Safety datalinks,64 a more recent analysis from seven US Vaccine
Safety Datalinks in the year following ACIP recommendations for antenatal Tdap
vaccination,50 a retrospective review of medical records of 1,759 women who
delivered a singleton infant in Texas during 2012-14,65 a prospective follow-up study
of 403 infants in New Zealand whose mothers had received Tdap antenatally
following a pertussis epidemic in 2012.67
Following recent national recommendations to vaccinate pregnant women in each
pregnancy in the US, the UK and elsewhere, irrespectively of previous history of
vaccine uptake, recent studies have attempted to assess the safety of repeated doses of
antenatal Tdap vaccination. An observational cohort study using data from seven
Vaccine Safety Datalink sites in the US evaluated acute adverse events and adverse
birth outcomes in 29155 women over a five year period.68 Women who were
vaccinated in pregnancy with Tdap were divided into three groups according to the
timing of prior receipt of Tdap: <2 years, 2-5 years and >5 years (the control group).
15
Overall, no differences were found in vaccine-associated (pyrexia, allergy or local
reactions) or pregnancy-associated (preterm delivery, low birth weight rate, SGA)
adverse events. It should, however, be noted that one of the exclusion criteria was
pregnancies with non-live birth outcomes (stillbirth, spontaneous abortion and ectopic
pregnancy).
In a retrospective, cohort study of 7378 women offered antenatal Tdap at 32 weeks
gestation at a single institution in Texas,69 there was no difference in the risk of
stillbirths, major malformations, chorioamnionitis, Apgar scores, cord blood pH or
neonatal complications such as ventilation requirement, sepsis, intraventricular
hemorrhage, or death. Interestingly, however, preterm birth before 37 weeks gestation
(6% vs. 12%, p <0·001), SGA (10% vs. 15%, p = 0·03), and duration of
hospitalisation (3·9 vs. 4·7 days, p <0·001) were all significantly higher in the
unvaccinated cohort. Notably, though, adverse neonatal outcomes were not
significantly different between the 1,229 women receiving >1 Tdap vaccine in the
previous five years and 4,159 women who received only a single dose.69 There are
also some safety data for Tdap administered in early pregnancy. In a single-centre,
retrospective study assessing pregnancy and birth outcomes in infants born to 138
women during 2005-09, 63% of whom had received Tdap in the first trimester,
mainly as vaccination against tetanus following trauma (many of the women were not
aware that they were pregnant at the time), there were no significant differences in
maternal (spontaneous or elective abortion) or infant (preterm delivery, gestational
age, birth weight, congenital anomalies or complex chronic conditions) outcomes
when compared to infants of 552 unvaccinated pregnant women.70
16
Table 2: Studies focusing on safety of pertussis-containing vaccines in pregnancy (n=10)
Country
(year of study)
Type of study Number of participants Main results/findings Reference
US
(2008-2012)
Randomised
Controlled Trial
33 Tdap vaccinated women versus 15 placebo No increased risk of AEs in pregnant women and infants Munoz et al, 2014
US
(2010-2012)
Retrospective observational 26229 Tdap vaccinated women versus 97265 unvaccinated No increased risk in preterm birth or SGA Kharbanda et al, 2014
UK
(2012-2013)
Retrospective observational 20074 Tdap vaccinated women versus matched unvaccinated
historical cohorts
No increased incidence of stillbirth Donegan et al, 2014
US
(2007-2013)
Retrospective cohort 29155 women - 3 groups according to timing of prior receipt of
vaccine: less than 2 years, 2-5 years and more than 5 years
(control)
No differences in maternal AEs and preterm delivery, low birth weight and SGA rate Sukumaran et al, 2015
US(Texas)
2013-2014
Retrospective cohort 7152 Tdap vaccinated women compared to 226 who declined -
4159 single dose compared to 1229 more doses
No difference in adverse obstetric or neonatal outcomes - preterm birth and duration
of hospitalization were significantly higher in the unvaccinated group
Morgan et al, 2015
US (Utah)
(2005-2009)
Retrospective 138 Tdap vaccinated women (63% during first trimester as
wound prophylaxis) versus 552 unvaccinated controls
No difference in adverse obstetric or neonatal outcomes Shakib et al, 2013
US (Texas)
(2012-2014)
Retrospective analysis
of electronic medical
records
1109 Tdap vaccinated women versus 650 non vaccinated No difference in obstetric (chorioamnionitis, preterm delivery, premature rupture of
membranes, induced labour, preterm delivery) or neonatal (SGA, low birth weight,
birth defects, NICU admission) outcomes
Berenson et al, 2016
US
(2007-2013)
Retrospective observational 53885 Tdap vaccinated pregnant women and 109253 matched
unvaccinated
No acute maternal safety events Kharbanda et al, 2016
New Zealand
(2014)
Prospective observational 403 infants of vaccinated mothers compared to baseline
population data
No adverse neonatal outcomes - no reported pertussis cases in infants despite high
prevalent disease rate
Walls et al, 2016
US
(2005-2010)
Retrospective 132 reports of Vaccine Adverse Events following Tdap
administration to pregnant women
No concerning patterns in maternal, infant, or foetal outcomes. Zheteyeva et al, 2012
AEs: adverse events, SGA: small for gestational age, NICU: Neonatal Intensive Care Unit
17
Effectiveness
The impact and effectiveness of antenatal pertussis immunisation has been reported
for the UK. In England and Wales, a 78% and 68% reduction in pertussis cases and
hospital admissions, respectively, was noted in infants younger than three months of
age during the first nine months of 2013 compared to the same period in 2012. The
antenatal vaccine coverage before delivery was 64%. Vaccine effectiveness based on
82 confirmed cases in infants born from October the 1st, 2012, and younger than 3
months was 91% (95% CI 84 to 95). When the analysis was restricted to cases in
those younger than 2 months, vaccine effectiveness was 90% (95% CI 82 to 95)71.
Similar vaccine effectiveness rates (93%; 95% CI, 81-97%) were reported in a
subsequent case control study conducted for infants aged < 8 weeks with confirmed
pertussis.72
Cost– Effectiveness
A number of studies have assessed the cost-effectiveness of maternal pertussis
vaccination in different countries. Antenatal vaccination against pertussis is
considered an effective strategy in preventing severe infant disease and deaths, but
cost-effectiveness depends – among other factors – highly on disease incidence,
which is difficult to predict. In the UK, if the incidence remained at the level of the
2012 epidemic, then antenatal immunisation would be a cost-effective intervention.73
A recent US study found antenatal vaccination to be cost-effective, in contrast to
vaccinating a second parent or vaccinating either parent post-partum.74 Economic
analysis in New Zealand also found that the addition of pertussis vaccination to the
New Zealand national antenatal immunisation program was a cost-effective or even
18
cost-saving decision.75 In Spain, it was estimated that 4,752 parents would need to be
vaccinated as part of a cocoon strategy to prevent one pertussis hospitalisation and
>900,000 to prevent one death.12 For antenatal immunisation, the numbers were 1,331
and 200,000, respectively, highlighting the cost-benefit compared with cocooning. In
Brazil, antenatal immunisation of one annual cohort had the potential to avoid 661
cases and 24 infant deaths, saving 1,800 years of life.76 Economic analysis indicated
universal antenatal Tdap immunisation would be a cost-effective intervention for
preventing pertussis cases and deaths in infants in Brazil.
CONLUSIONS
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. Pregnant women produce high concentrations of vaccine-
induced antibodies and can offer protection to their offspring through efficient
transplacental antibody transfer. The introduction of antenatal vaccination against
pertussis into a national immunisation programme will depend on a range of local
factors, especially disease incidence, vaccine costs, implementation barriers and cost-
effectiveness analyses. Narrowing the gap between scientific evidence and public
health policies is critical in order to protect the most vulnerable as quickly as possible.
Given the initial safety and efficacy concerns of off-license antenatal immunisation,
the rapid and sustained 60% coverage achieved in the UK is commendable. There are,
however, opportunities to improve vaccine coverage in all countries that currently
recommend antenatal immunisation against pertussis, through education of the public,
vaccine givers, and all primary and secondary healthcare professionals who have any
19
contact with pregnant women and improvements in access to vaccine to ensure
timely immunisation. There is also a need for on-going surveillance to monitor
disease activity, safety and long-term vaccine impact. The lessons learnt will be vital
for the introduction of new antenatal vaccines, including those against Respiratory
Syncytial Virus (RSV) and Group B Streptococcus (GBS), which are currently under
development and will further reduce neonatal morbidity and mortality in the near
future.
20
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