Safety of the Pandemic H1N1 Influenza Vaccine Among Pregnant U.S. Military Women and Their Newborns

Maternal Vaccine Effectiveness Against Influenza-Associated Hospitalizations and Emergency Department Visits in Infants

Importance

Influenza virus infection during pregnancy is associated with severe maternal disease and may be associated with adverse birth outcomes. Inactivated influenza vaccine during pregnancy is safe and effective and can protect young infants, but recent evidence, particularly after the 2009 novel influenza A (H1N1) pandemic, is limited.

Objective

To evaluate the effectiveness of influenza vaccination during pregnancy against laboratory-confirmed influenza-associated hospitalizations and emergency department (ED) visits in infants younger than 6 months.

Design, Setting, and Participants

This was a prospective, test-negative case-control study using data from the New Vaccine Surveillance Network from the 2016 to 2017 through 2019 to 2020 influenza seasons. Infants younger than 6 months with an ED visit or hospitalization for acute respiratory illness were included from 7 pediatric medical institutions in US cities. Control infants with an influenza-negative molecular test were included for comparison. Data were analyzed from June 2022 to September 2023.

Exposure

Maternal influenza vaccination during pregnancy.

Main Outcomes and Measures

We estimated maternal vaccine effectiveness against hospitalizations or ED visits in infants younger than 6 months, those younger than 3 months, and by trimester of vaccination. Maternal vaccination status was determined using immunization information systems, medical records, or self-report. Vaccine effectiveness was estimated by comparing the odds of maternal influenza vaccination 14 days or more before delivery in infants with influenza vs those without.

Results

Of 3764 infants (223 with influenza and 3541 control infants), 2007 (53%) were born to mothers who were vaccinated during pregnancy. Overall vaccine effectiveness in infants was 34% (95% CI, 12 to 50), 39% (95% CI, 12 to 58) against influenza-associated hospitalizations, and 19% (95% CI, -24 to 48) against ED visits. Among infants younger than 3 months, effectiveness was 53% (95% CI, 30 to 68). Effectiveness was 52% (95% CI, 30 to 68) among infants with mothers who were vaccinated during the third trimester and 17% (95% CI, -15 to 40) among those with mothers who were vaccinated during the first or second trimesters.

Conclusions and Relevance

Maternal vaccination was associated with reduced odds of influenza-associated hospitalizations and ED visits in infants younger than 6 months. Effectiveness was greatest among infants younger than 3 months, for those born to mothers vaccinated during the third trimester, and against influenza-associated hospitalizations.

Safety of influenza vaccination during pregnancy: a systematic review

OBJECTIVE

We conducted a systematic review to evaluate associations between influenza vaccination during pregnancy and adverse birth outcomes and maternal non-obstetric serious adverse events (SAEs), taking into consideration confounding and temporal biases.

METHODS

Electronic databases (Ovid MEDLINE ALL, Embase Classic+Embase and the Cochrane Central Register of Controlled Trials) were searched to June 2021 for observational studies assessing associations between influenza vaccination during pregnancy and maternal non-obstetric SAEs and adverse birth outcomes, including preterm birth, spontaneous abortion, stillbirth, small-for-gestational-age birth and congenital anomalies. Studies of live attenuated vaccines, single-arm cohort studies and abstract-only publications were excluded. Records were screened using a liberal accelerated approach initially, followed by a dual independent approach for full-text screening, data extraction and risk of bias assessment. Pairwise meta-analyses were conducted, where two or more studies met methodological criteria for inclusion. The Grading of Recommendations, Assessment, Development and Evaluation approach was used to assess evidence certainty.

RESULTS

Of 9443 records screened, 63 studies were included. Twenty-nine studies (24 cohort and 5 case-control) evaluated seasonal influenza vaccination (trivalent and/or quadrivalent) versus no vaccination and were the focus of our prioritised syntheses; 34 studies of pandemic vaccines (2009 A/H1N1 and others), combinations of pandemic and seasonal vaccines, and seasonal versus seasonal vaccines were also reviewed. Control for confounding and temporal biases was inconsistent across studies, limiting pooling of data. Meta-analyses for preterm birth, spontaneous abortion and small-for-gestational-age birth demonstrated no significant associations with seasonal influenza vaccination. Immortal time bias was observed in a sensitivity analysis of meta-analysing risk-based preterm birth data. In descriptive summaries for stillbirth, congenital anomalies and maternal non-obstetric SAEs, no significant association with increased risk was found in any studies. All evidence was of very low certainty.

CONCLUSIONS

Evidence of very low certainty suggests that seasonal influenza vaccination during pregnancy is not associated with adverse birth outcomes or maternal non-obstetric SAEs. Appropriate control of confounding and temporal biases in future studies would improve the evidence base.

Impact of major disease outbreaks in the third millennium on adolescent and youth sexual and reproductive health and rights in low and/or middle-income countries: a systematic scoping review protocol

INTRODUCTION

Sexual and Reproductive Health and Rights (SRHR) of young people continue to present a high burden and remain underinvested. This is more so in low and middle-income countries (LMICs), where empirical evidence reveals disruption of SRHR maintenance, need for enhancement of programmes, resources and services during pandemics. Despite the importance of the subject, there is no published review yet combining recent disease outbreaks such as (H1N1/09, Zika, Ebola and SARS-COV-2) to assess their impact on adolescents and youth SRHR in LMICs.

METHODS AND ANALYSIS

We will adopt a four-step search to reach the maximum possible number of studies. In the first step, we will carry out a limitedpreliminary search in databases for getting relevant keywords (appendix 1). Second, we will search in four databases: Pubmed, Cochrane Library, Embase and PsycINFO. The search would begin from the inception of the first major outbreak in 2009 (H1N1/09) up to the date of publication of the protocol in early 2022. We will search databases using related keywords, screen title & abstract and review full texts of the selected titles to arrive at the list of eligible studies. In the third stage, we will check their eligibility to the included article's reference list. In the fourth stage, we will check the citations of included papers in phase 2 to complete our study selection. We will include all types of original studies and without any language restriction in our final synthesis. Our review results will be charted for each pandemic separately and include details pertaining to authors, year, country, region of the study, study design, participants (disaggregated by age and gender), purpose and report associated SRHR outcomes. The review will adhere to the Preferred Reporting Items for Systematic reviews and Meta-Analyses extension for Scoping Reviews guideline (PRISMA-ScR).

PATIENT AND PUBLIC INVOLVEMENT

Patients or public were not involved in this study.

ETHICS AND DISSEMINATION

Ethical assessment is not required for this study. The results of the study will be presented in peer-reviewed publications and conferences on adolescent SRHR.

History of pandemic H1N1-containing influenza vaccination and risk for spontaneous abortion and birth defects

BACKGROUND

One recent study suggested an association between receipt of pandemic H1N1 (pH1N1)-containing vaccines in consecutive influenza seasons and spontaneous abortion, but corroborating scientific evidence is limited. In the present study, we leveraged a population of vaccine-compliant pregnant military women to examine history of pH1N1-containing influenza vaccination and adverse pregnancy outcomes. Because seasonal influenza vaccination is compulsory for military service, safety concerns regarding repeat vaccination are particularly relevant in this population.

METHODS

Pregnancies and live births from Department of Defense Birth and Infant Health Research program data were linked with military personnel immunization records to identify women vaccinated with a pH1N1-containing vaccine in pregnancy prior to 21 6/7 weeks' gestation, October 2009-April 2015. Cox and modified Poisson regression models estimated associations between vaccination with pH1N1- versus non-pH1N1-containing influenza vaccine in the season prior to the index pregnancy, and spontaneous abortion and birth defects, respectively. Cox models were calculated for two periods of follow-up: through (1) 21 6/7 weeks' gestation and (2) 28 days postvaccination.

RESULTS

Of 26,264 pregnancies, 21,736 (82.8%) were among women who received a dose of pH1N1-containing vaccine in the prior influenza season and 4,528 (17.2%) were among women who received non-pH1N1-containing vaccine in the prior influenza season. Among 23,121 infants, 19,365 (83.8%) and 3,756 (16.2%) had mothers exposed and unexposed to pH1N1-containing vaccine in the prior influenza season, respectively. The adjusted hazard ratio (aHR) for spontaneous abortion approximated 1.0 across the complete follow-up period (95% confidence interval [CI]: 0.89-1.13) and was slightly elevated when censored at 28 days postvaccination, though the CI was imprecise (aHR: 1.19; 95% CI: 0.97-1.46). No associations with birth defects were observed.

CONCLUSION

This work lends additional safety evidence and support for vaccination against pH1N1 in pregnancy, regardless of the vaccine received in the prior influenza season.

A Scoping Review of Pregnancy, Childbirth, and the Postpartum Period in Active Duty U.S. Military Women

PURPOSE

Women in the U.S. military encounter unique challenges during the perinatal period that are driven by military requirements for mission readiness. The purpose of this scoping review was to systematically examine the extent, range, and nature of the literature on pregnancy, childbirth, and the postpartum period of active duty military women. A secondary aim was to identify leverage points for changes to improve perinatal health of servicewomen.

METHODS

We used a PRISMA-ScR protocol to guide this scoping review of research and non-research articles germane to the perinatal health of servicewomen. In the protocol, we identified the rationale, objectives, eligibility criteria, search strategy, sources of evidence, and data charting processes for the review. We used the social ecological model for military women's health framework to guide the synthesis of results.

FINDINGS

Eighty-four articles on the topics of pregnancy, childbirth, and the postpartum period of servicewomen published from 2000 to 2018 were identified. The articles were mainly research studies (n = 76), of which 49 had observational designs. Leverage points to promote workplace safety and support of pregnant women, perinatal screening, recognition of pregnancy and postpartum depression, and maintaining physical fitness during pregnancy and the postpartum period were identified in multiple levels of the social ecological model for military women's health.

CONCLUSIONS

Literature published from 2000 to 2018 is broad in scope, yet generally lacks a robust body of evidence on any one topic. Implementing strategies and military policies that are directed at the identified leverage points could enhance the health of childbearing servicewomen.

Racial Disparities in Prenatal Care Utilization and Infant Small for Gestational Age Among Active Duty US Military Women

OBJECTIVES

To examine racial disparities in prenatal care (PNC) utilization and infant small for gestational age (SGA) among active duty US military women, a population with equal access to health care and known socioeconomic status.

METHODS

Department of Defense Birth and Infant Health Research program data identified active duty women with singleton live births from January 2003 through August 2015. Administrative claims data were used to define PNC utilization and infant SGA, and log-binomial regression models estimated associations with race/ethnicity. To examine whether associations between maternal race/ethnicity and infant SGA were subject to effect measure modification, respective analyses were stratified by demographic and health characteristics.

RESULTS

Overall, 12.2% of non-Hispanic White women initiated PNC after the first trimester, compared with 14.8% of American Indian/Alaska Native, 15.1% of Asian/Pacific Islander, 14.2% of non-Hispanic Black, and 13.0% of Hispanic women. Infant SGA prevalence was 2.4% and 1.6% among non-Hispanic Black and White women, respectively (aRR 1.52, 95% CI 1.40-1.64). This disparity persisted across stratified analyses, particularly among non-Hispanic Black versus White women with a preeclampsia or hypertension diagnosis in pregnancy (RR 1.96, 95% CI 1.67-2.29) and those aged 35 + years at infant birth (RR 2.04, 95% CI 1.56-2.67).

CONCLUSIONS FOR PRACTICE

In multiple assessments of PNC utilization and infant SGA, non-Hispanic Black military women had consistently worse outcomes than their non-Hispanic White counterparts. This suggests that equal access to health care does not eliminate racial disparities in outcomes or utilization; additional research is needed to elucidate the underlying etiology of these disparities.

Safety of yellow fever vaccination in pregnancy: findings from a cohort of active duty US military women

BACKGROUND

Yellow fever (YF) is a rare viral disease that can be prevented through receipt of a live attenuated vaccine. In the US military, service members must receive the YF vaccine before assignment to endemic areas, putting active duty service women at heightened risk for inadvertent exposure during preconception or pregnancy. Few studies have investigated the safety of YF vaccination in pregnancy to date, and none in a military population.

METHODS

Department of Defense Birth and Infant Health Research program data were used to identify pregnancies and infants among active duty US military women, 2003-2014. Multivariable regression models estimated associations with YF vaccine exposure during preconception/pregnancy and adverse outcomes (e.g. spontaneous abortion, birth defects). Sensitivity analyses were performed that excluded pregnancies exposed to other live vaccines. For analyses of birth defects only, a secondary sensitivity analysis was performed that excluded infants diagnosed with chromosomal anomalies.

RESULTS

Of the 196 802 pregnancies and 160 706 singleton infants identified, 1347 (0.7%) and 1132 (0.7%), respectively, were exposed to the YF vaccine. No increased risks for adverse pregnancy or infant outcomes were observed in the main analysis. In sensitivity analyses that excluded pregnancies exposed to other live vaccines, preconception YF vaccine exposure was associated with birth defects [adjusted risk ratio (aRR) = 1.71, 95% confidence interval (CI) = 1.08-2.73]; this association was attenuated when further excluding infants with chromosomal anomalies (aRR = 1.59, 95% CI = 0.97-2.62).

CONCLUSIONS

Overall, YF vaccine exposure did not appear to be associated with most adverse outcomes among this population of pregnant military women. A tenuous association between preconception YF vaccine exposure and birth defects was observed in sensitivity analyses, which may warrant further investigation.

Maternal and infant outcomes following exposure to quadrivalent human papillomavirus vaccine during pregnancy

INTRODUCTION

The Department of Defense encourages service members ≤26 years of age to receive the human papillomavirus (HPV) vaccine. Although this vaccine is not recommended in pregnancy, inadvertent vaccination may occur. The objective of this study was to assess whether active duty US military women who received the quadrivalent HPV vaccine (4vHPV) during pregnancy were at increased risk for adverse maternal or infant outcomes.

METHODS

The study population included active duty US military women aged 17-28 years with at least one pregnancy between 2007 and 2014, and the infants resulting from those pregnancies. Pregnancies, live births, and outcomes were identified using medical codes in administrative medical records. Exposure to 4vHPV during pregnancy was ascertained from personnel immunization records. Multivariable regression models were used to calculate risk estimates and 95% confidence intervals for the maternal outcomes of spontaneous abortion, preeclampsia/eclampsia and preterm labor, and the infant outcomes of preterm birth, birth defects, growth problems in infancy or in utero, and infant sex.

RESULTS

Overall, 90,600 pregnancies and 75,670 singleton infants were identified. Approximately 2% of pregnancies and infants were exposed to 4vHPV during pregnancy. After adjustments, no positive associations were detected between inadvertent exposure to 4vHPV during pregnancy and any adverse pregnancy or infant outcomes.

DISCUSSION

Our findings add to an established body of literature demonstrating the safety of 4vHPV when inadvertently administered during pregnancy. Although 4vHPV is no longer administered in the US, its use continues overseas; therefore, safety studies remain important. Furthermore, such studies can provide reassurance to women inadvertently exposed to nonavalent HPV vaccine (9vHPV) in pregnancy, which protects against four of the same antigens as 4vHPV, since safety of 9vHPV has not yet been established in pregnant women.

Safety and immunogenicity of three seasonal inactivated influenza vaccines among pregnant women and antibody persistence in their infants

OBJECTIVE

Inactivated influenza virus vaccines (IIVs) are recommended for all pregnant women in the United States. We conducted a prospective, randomized, double blind study of three licensed seasonal trivalent IIVs (IIV3s) to assess their safety and immunogenicity in pregnant women and determine the level and persistence of passively transferred maternal antibody in infants.

STUDY DESIGN

139 pregnant women ages 18-39 years and 14-33 weeks' gestation, and 44 non-pregnant women, were randomized 1:1:1 to receive a single intramuscular dose of one of three licensed IIV3s (Agriflu®, Fluzone®, or Fluarix®) prior to the 2010-2011 influenza season. Reactogenicity, adverse events (AEs) and pregnancy outcomes were documented. Serum samples for hemagglutination inhibition (HAI) and neutralization antibody assays were collected prior to and 28 and 180 days after immunization. Maternal sera and cord blood were collected at the time of delivery and sera were obtained from 44 infants at 6 weeks of age.

RESULTS

Pregnant and non-pregnant women experienced similar frequency of injection site (92% and 86%, respectively) and systemic (95% and 87%, respectively) reactions, the majority of which were mild. There were no vaccine-associated maternal or infant serious AEs. Antibody responses to the three vaccine antigens were not different between pregnant and non-pregnant women. The ratios of cord blood (infant) to maternal HAI antibody titers at delivery ranged between 1.1 and 1.7 for each of the vaccine antigens. Influenza antibody concentrations in infants were 70-40% of the birth titer by 6 weeks of age.

CONCLUSIONS

The three IIV3s were well tolerated in pregnant women. Antibody responses were comparable in pregnant and non-pregnant women, and after second or third trimester vaccination. Transplacental transfer of maternal antibodies to the infant was efficient. However, antibody titers decline rapidly in the first 6 weeks of life.

Australian Veterans of the Middle East Conflicts 2001–2010: Select Reproductive Health Outcomes Part 2 — Prenatal, Fetal, and Neonatal Outcomes

Background: Following on from Part 1 of these companion articles, which described the maternal and paternal cohort of the Middle East Area of Operations (MEAO) Census Study, this manuscript aims to describe fetal and infant characteristics and outcomes from the self-report data, including live deliveries, stillbirths, all other pregnancy losses, and unknown outcomes.

Methods: A descriptive analysis was performed on the clinical variables where data were reported. Descriptive statistics (means, frequencies, percentiles) were used to describe the occurrence of adverse gestational outcomes. Odds ratios were also calculated for perinatal outcomes. Infant characteristics and outcomes were evaluated using statistical analysis software IBM SPSS v26.

Results: There were 15,417 pregnancies reported by respondents to the MEAO Census Study. Of these, 74% (11,367) resulted in a live delivery, 0.75% in a stillbirth, and 20% in another type of pregnancy loss (ectopic pregnancy, miscarriage, termination). The unadjusted odds of an adverse perinatal outcome were higher in the MEAO Census population than in the general Australian population, notably stillbirth (OR = 3.11, 95% CI 2.56–3.80), perinatal death (OR = 3.80, 95% CI 3.26–4.44), and neonatal death (OR = 5.43, 95% CI 4.27–6.91). There were 499 cases of birth defects reported and 85 cases of childhood cancer in the MEAO population. The unadjusted odds of childhood cancer were slightly higher (OR = 1.7, 95% CI 0.09–3.28) in the MEAO population, and the unadjusted odds of birth defects were lower (OR = 0.52, 95% CI 0.40–0.68). The male:female infant sex ratio of babies born to respondents was 102 (5939 males:5823 females).

Conclusions: The MEAO Census Study presents a generally reassuring picture of reproductive health for women serving in the Australian Defence Force with regards to the risk of pregnancy loss and perinatal outcomes. The increased odds of perinatal and neonatal death and stillbirth are worthy of further study and evaluation, as is the increase in likelihood of childhood cancer in the offspring of MEAO veterans.

Obstetric Outcomes in Military Servicewomen: Emerging Knowledge, Considerations, and Gaps

The number of women in the U.S. military is dramatically increasing. Similarly, the roles of active-duty women are greatly expanding, thus exposing them to new occupational risks. Determining the impact of pregnancy outcomes for women while in the military is difficult due to changing exposures over time, difficulty in utilizing appropriate comparison groups, and the lack of prospective investigations. Despite these limitations, it was concerning that the available data suggest that servicewomen delivering within 6 months of their first deployment have an increased preterm birth risk (adjusted odds ratio [aOR]: 2.1), and those with three prior deployments have an even greater risk (aOR: 3.8). Servicewomen also have an increased risk of hypertensive disorders with a rate of 13% compared with 5% in the general obstetric population. Furthermore, depression is higher for women who deploy after childbirth and are exposed to combat when compared with those who have not deployed since the birth of their child (aOR: 2.01). Due to the importance of this issue, prospective research designs are necessary to better understand and address the unique health care needs of this population.

Japanese encephalitis vaccination in pregnancy among U.S. active duty military women

INTRODUCTION

Japanese encephalitis (JE) vaccine is an inactivated vaccine that has shown no risks in pregnancy in animal models, but epidemiologic studies are lacking. U.S. military service members located in JE endemic regions are required to be vaccinated; understanding the potential adverse events (AEs), including AEs that may occur in pregnancy, is needed. Here, we assessed pregnancy and infant health outcomes in association with JE vaccination in pregnancy.

METHODS

The study population consisted of 192,570 pregnancies to active duty women (2003-2014), captured in the Department of Defense Birth and Infant Health Research program. JE vaccine in pregnancy, vaccine count, formulation, trimester, and whether first career dose coincided with pregnancy were compared with unexposed pregnancies to assess risk of pregnancy and infant health outcomes. Adjusted risk estimates and 95% confidence intervals (CIs) were calculated by multivariable models.

RESULTS

Of the 192,570 identifed pregnancies, 513 were exposed to the JE vaccine; 474 exposures occurred in the first trimester. For all outcomes, elevated risk estimates ranging from 1.53 to 1.70, were observed with receipt of >1 JE vaccine in pregnancy, though 95% CIs were wide and encompassed the null. First dose of JE vaccination in pregnancy was associated with a 1.87 (95% CI: 1.12-3.13) times increased risk of low birthweight (LBW) when excluding pregnancies exposed to other non-routinely recommended vaccinations in pregnancy. All other associations were null in both main and subset analyses.

CONCLUSIONS

The overall results of these analyses provide reassuring findings for the safety of JE vaccination in pregnancy. Higher counts of JE vaccine received in pregnancy yielded large yet non-statistically significant risk estimates for all outcomes, though likely driven by lack of pregnancy awareness. An association was observed with LBW in subset analyses, but it was limited to women receiving their first JE vaccine and not observed in the larger main analyses.

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

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

Safety of tetanus, diphtheria, and acellular pertussis vaccination among pregnant active duty U.S. military women

BACKGROUND

The tetanus, diphtheria, and acellular pertussis (Tdap) vaccine was approved for U.S. adults in 2005 and recommended for administration in every pregnancy in 2012, with optimal timing between 27 and 36 weeks' gestation. In the military, however, a current Tdap vaccination status is compulsory for service, and active duty women may be inadvertently exposed in early pregnancy. Safety data in this population are limited.

OBJECTIVES

To assess safety of inadvertent (0-13 weeks' gestation) and recommended (27-36 weeks' gestation) exposure to the Tdap vaccine in pregnancy.

METHODS

Pregnancies and live births from Department of Defense Birth and Infant Health Research program data were linked with military personnel immunization records to determine pregnancy Tdap vaccine exposure among active duty women, 2006-2014. Multivariable Cox and generalized linear regression models estimated associations between Tdap vaccine exposure and adverse pregnancy or infant outcomes.

RESULTS

Of 145,883 pregnancies, 1272 were exposed to the Tdap vaccine in the first trimester and 9438 between 27 and 36 weeks' gestation. Neither inadvertent nor recommended vaccine exposure were associated with spontaneous abortion, preeclampsia, or preterm labor. Among 117,724 live born infants, 984 were exposed to the Tdap vaccine in the first trimester and 9352 between 27 and 36 weeks' gestation. First trimester exposure was not associated with birth defects, growth problems in utero, growth problems in infancy, preterm birth, or low birth weight. Tdap vaccine exposure between 27 and 36 weeks' gestation was not associated with any adverse infant outcome.

CONCLUSIONS

Among a population of active duty women in the U.S. military who received the Tdap vaccine during pregnancy, we detected no increased risks for adverse maternal, fetal, or infant outcomes. Our findings corroborate existing literature on the safety of exposure to the Tdap vaccine in pregnancy.

Effects of maternal influenza vaccination on adverse birth outcomes: A systematic review and Bayesian meta-analysis

BACKGROUND

Although pregnant women are a priority group for influenza vaccination, its effect on birth outcomes has long been debated. Numerous observational studies and a few randomized controlled studies have been conducted, with inconsistent results.

OBJECTIVES

To evaluate the association of influenza vaccination in pregnancy with adverse birth outcomes.

DATA SOURCE

The Cochrane Library, PubMed, EMBASE, Web of Science, and Scopus were searched.

STUDY ELIGIBILITY CRITERIA

This analysis included randomized placebo-controlled studies, cohort studies, and case-control studies, in which inactivated influenza vaccination was given during pregnancy and fetal adverse birth outcomes were assessed.

PARTICIPANTS & INTERVENTION

Women who received inactivated influenza vaccine during pregnancy and their offspring.

STUDY APPRAISAL AND SYNTHESIS

Two independent reviewers and a third reviewer collaborated in study selection and data extraction. A Bayesian 3-level random-effects model was utilized to assess the impact of maternal influenza vaccination on birth outcomes, which were presented as odds ratios (ORs) with 95% credible interval (CrIs). Bayesian outcome probabilities (P) of an OR<1 were calculated, and values of at least 90% (0.9) were deemed to indicate a significant result.

RESULTS

Among the 6,249 identified publications, 48 studies were eligible for the meta-analysis, including 2 randomized controlled trials, 41 cohort studies, and 5 case-control studies. The risk of none of the following adverse birth outcomes decreased significantly: preterm birth (OR = 0.945, 95% CrI: 0.736-1.345, P = 73.3%), low birth weight (OR = 0.928, 95% CrI: 0.432-2.112, P = 76.7%), small for gestational age (OR = 0.971, 95% CrI: 0.249-4.217,P = 63.3%), congenital malformation (OR = 1.026, 95% CrI: 0.687-1.600, P = 38.0%), and fetal death (OR = 0.942, 95% CrI: 0.560-1.954, P = 61.6%). Summary estimates including only cohort studies showed significantly decreased risks for preterm birth, small for gestational age and fetal death. However, after adjusting for season at the time of vaccination and countries' income level, only fetal death remained significant.

CONCLUSION

This Bayesian meta-analysis did not find a protective effect of maternal influenza vaccination against adverse birth outcomes, as reported in previous studies. In fact, our results showed evidence of null associations between maternal influenza vaccination and adverse birth outcomes.

Birth outcomes following immunization of pregnant women with pandemic H1N1 influenza vaccine 2009-2010

BACKGROUND

Following the H1N1 influenza pandemic in 2009, pregnant women were recommended to receive both seasonal (TIV) and H1N1 influenza vaccines. This study presents incidence of adverse birth and pregnancy outcomes among a population of pregnant women immunized with TIV and H1N1 vaccines at Kaiser Permanente Northern California during 2009-2010.

METHODS

We telephone surveyed pregnant Kaiser Permanente Northern California members to assess non-medically-attended reactions following H1N1, TIV or both vaccines during 2009-2010 (n=5365) in a separate study. Here we assessed preterm birth (<37weeks), very preterm birth (<32weeks), low birth weight (<2500 g, LBW), very low birth weight (<1500g), small for gestational age, spontaneous abortions, stillbirths and congenital anomalies among this cohort by comparing incidence and 95% confidence intervals between the following immunization groups: TIV only, H1N1 only, H1N1 prior to TIV immunization, TIV prior to H1N1 and both immunizations given at the same time.

RESULTS

Results did not vary significantly between groups. Comparing H1N1 with TIV, incidence were similar for preterm births (6.37vs 6.28/100 births), very preterm births (5.30vs 8.29/1000 births), LBW (4.19vs 2.90/100 births), very LBW (4.54vs 5.52/1000 births), small for gestational age (9.99vs 9.24/1000 births), spontaneous abortion (7.10vs 6.83/1000 pregnancies), stillbirths (7.10vs 4.57/1000 pregnancies), and congenital anomalies (2.66vs 2.43/100 births).

CONCLUSIONS

Although constrained by small sample size, complex vaccine groups, and differential vaccine availability during 2009-2010, this study found no difference in adverse birth outcomes between H1N1 vaccine and TIV.

Vaccines for preventing influenza in healthy adults

BACKGROUND

The consequences of influenza in adults are mainly time off work. Vaccination of pregnant women is recommended internationally. This is an update of a review published in 2014. Future updates of this review will be made only when new trials or vaccines become available. Observational data included in previous versions of the review have been retained for historical reasons but have not been updated due to their lack of influence on the review conclusions.

OBJECTIVES

To assess the effects (efficacy, effectiveness, and harm) of vaccines against influenza in healthy adults, including pregnant women.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL; 2016, Issue 12), MEDLINE (January 1966 to 31 December 2016), Embase (1990 to 31 December 2016), the WHO International Clinical Trials Registry Platform (ICTRP; 1 July 2017), and ClinicalTrials.gov (1 July 2017), as well as checking the bibliographies of retrieved articles.

SELECTION CRITERIA

Randomised controlled trials (RCTs) or quasi-RCTs comparing influenza vaccines with placebo or no intervention in naturally occurring influenza in healthy individuals aged 16 to 65 years. Previous versions of this review included observational comparative studies assessing serious and rare harms cohort and case-control studies. Due to the uncertain quality of observational (i.e. non-randomised) studies and their lack of influence on the review conclusions, we decided to update only randomised evidence. The searches for observational comparative studies are no longer updated.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed trial quality and extracted data. We rated certainty of evidence for key outcomes (influenza, influenza-like illness (ILI), hospitalisation, and adverse effects) using GRADE.

MAIN RESULTS

We included 52 clinical trials of over 80,000 people assessing the safety and effectiveness of influenza vaccines. We have presented findings from 25 studies comparing inactivated parenteral influenza vaccine against placebo or do-nothing control groups as the most relevant to decision-making. The studies were conducted over single influenza seasons in North America, South America, and Europe between 1969 and 2009. We did not consider studies at high risk of bias to influence the results of our outcomes except for hospitalisation.Inactivated influenza vaccines probably reduce influenza in healthy adults from 2.3% without vaccination to 0.9% (risk ratio (RR) 0.41, 95% confidence interval (CI) 0.36 to 0.47; 71,221 participants; moderate-certainty evidence), and they probably reduce ILI from 21.5% to 18.1% (RR 0.84, 95% CI 0.75 to 0.95; 25,795 participants; moderate-certainty evidence; 71 healthy adults need to be vaccinated to prevent one of them experiencing influenza, and 29 healthy adults need to be vaccinated to prevent one of them experiencing an ILI). The difference between the two number needed to vaccinate (NNV) values depends on the different incidence of ILI and confirmed influenza among the study populations. Vaccination may lead to a small reduction in the risk of hospitalisation in healthy adults, from 14.7% to 14.1%, but the CI is wide and does not rule out a large benefit (RR 0.96, 95% CI 0.85 to 1.08; 11,924 participants; low-certainty evidence). Vaccines may lead to little or no small reduction in days off work (-0.04 days, 95% CI -0.14 days to 0.06; low-certainty evidence). Inactivated vaccines cause an increase in fever from 1.5% to 2.3%.We identified one RCT and one controlled clinical trial assessing the effects of vaccination in pregnant women. The efficacy of inactivated vaccine containing pH1N1 against influenza was 50% (95% CI 14% to 71%) in mothers (NNV 55), and 49% (95% CI 12% to 70%) in infants up to 24 weeks (NNV 56). No data were available on efficacy against seasonal influenza during pregnancy. Evidence from observational studies showed effectiveness of influenza vaccines against ILI in pregnant women to be 24% (95% CI 11% to 36%, NNV 94), and against influenza in newborns from vaccinated women to be 41% (95% CI 6% to 63%, NNV 27).Live aerosol vaccines have an overall effectiveness corresponding to an NNV of 46. The performance of one- or two-dose whole-virion 1968 to 1969 pandemic vaccines was higher (NNV 16) against ILI and (NNV 35) against influenza. There was limited impact on hospitalisations in the 1968 to 1969 pandemic (NNV 94). The administration of both seasonal and 2009 pandemic vaccines during pregnancy had no significant effect on abortion or neonatal death, but this was based on observational data sets.

AUTHORS' CONCLUSIONS

Healthy adults who receive inactivated parenteral influenza vaccine rather than no vaccine probably experience less influenza, from just over 2% to just under 1% (moderate-certainty evidence). They also probably experience less ILI following vaccination, but the degree of benefit when expressed in absolute terms varied across different settings. Variation in protection against ILI may be due in part to inconsistent symptom classification. Certainty of evidence for the small reductions in hospitalisations and time off work is low. Protection against influenza and ILI in mothers and newborns was smaller than the effects seen in other populations considered in this review.Vaccines increase the risk of a number of adverse events, including a small increase in fever, but rates of nausea and vomiting are uncertain. The protective effect of vaccination in pregnant women and newborns is also very modest. We did not find any evidence of an association between influenza vaccination and serious adverse events in the comparative studies considered in this review. Fifteen included RCTs were industry funded (29%).

A systematic review of ethical issues in vaccine studies involving pregnant women

BACKGROUND

Immunization during pregnancy can provide protection for mother and child. However, there have been only a limited number of studies documenting the efficacy and safety of this strategy.

AIMS

To determine the extent and nature of subject matter related to ethics in maternal immunization by systematically documenting the spectrum of ethical issues in vaccine studies involving pregnant women.

METHOD

We conducted a systematic literature review of published works pertaining to vaccine and therapeutic studies involving pregnant women through searches of PubMed, EMBASE, Web of Science, the Cochrane Database, and ClinicalTrials.gov. We selected literature meeting the inclusion criteria published between 1988 and June 2014. We systematically abstracted subject matter pertaining to ethical issues in immunization studies during pregnancy. Immunization-specific ethical issues were matched and grouped into major categories and subcategories.

RESULTS

Seventy-seven published articles met the inclusion criteria. Published articles reported findings on data that had been collected in 26 countries, the majority of which were classified as high-income or upper-middle-income nations according to World Bank criteria. Review of these publications produced 60 immunization-specific ethical issues, grouped into six major categories. Notably, many studies demonstrated limited acknowledgment of key ethical issues including the rights and welfare of participants. Additionally, there was no discussion pertaining to the ethics of program implementation, including integration of maternal immunization programs into existing routine immunization programs.

CONCLUSION

This review of ethical issues in immunization studies of pregnant women can be used to help inform future vaccine trials in this important population. Consistent documentation of these ethical issues by investigators will facilitate a broader and more nuanced discussion of ethics in immunization of pregnant women - offering new and valuable insights for programs developed to prevent disease in newborn children in low- and middle-income countries.

Maternal Influenza Vaccination and Risk for Congenital Malformations: A Systematic Review and Meta-analysis

OBJECTIVE

To systematically summarize the literature on maternal influenza vaccination and the risk for congenital malformations using the methodology of meta-analysis.

DATA SOURCES

PubMed, Scopus, and Embase databases (up to December 2014) as well as ClinicalTrials.gov (May 2015) and references of relevant articles were searched. The search strategy included combinations of the terms "influenza," "vaccin*," "pregnan*," "safe*," "adverse," "congenital," "malformation," "defect," and "anomal*."

METHODS OF STUDY SELECTION

Eligible studies examined the association between antepartum or preconceptional maternal immunization with inactivated influenza vaccines (seasonal trivalent or monovalent H1N1) and the risk for congenital malformations. Studies with no or inappropriate control group (comparison with population background rates or other vaccine types) were excluded.

TABULATION, INTEGRATION, AND RESULTS

The risk for congenital anomalies after influenza vaccination was examined in 15 studies: 14 cohorts (events per vaccinated compared with unvaccinated: 859/32,774 [2.6%] compared with 7,644/245,314 [3.1%]) and one case-control study (vaccinated per cases compared with controls: 1,351/3,618 [37.3%] compared with 511/1,225 [41.7%]). Eight studies reported on first-trimester immunization (events per vaccinated compared with unvaccinated: 258/4,733 [5.4%] compared with 6,470/196,054 [3.3%]). No association was found between congenital defects and influenza vaccination at any trimester of pregnancy (odds ratio [OR] 0.96, 95% confidence interval 0.86-1.07; 15 studies; I2=36) or at the first trimester (OR 1.03, 0.91-1.18; eight studies; I2=0). When assessing only major malformations, no increased risk was detected after immunization at any trimester (OR 0.99, 0.88-1.11; 12 studies; I2=31.5) or at the first trimester (OR 0.98, 0.83-1.16; seven studies; I2=0). Neither adjuvanted (OR 1.06, 0.95-1.20; five studies; I2=18.8) nor unadjuvanted vaccines (OR 0.89, 0.75-1.04; seven studies; I2=22.6) were associated with an increased risk for congenital defects.

CONCLUSION

This systematic review did not indicate an increased risk for congenital anomalies after maternal influenza immunization adding to the evidence base on the safety of influenza vaccination in pregnancy.

A systematic review of adverse events following immunization during pregnancy and the newborn period

In 2013, the WHO Strategic Advisory Group of Experts on Immunization (SAGE) requested WHO to develop a process and a plan to move the maternal immunization agenda forward in support of an increased alignment of data safety evidence, public health needs, and regulatory processes. A key challenge identified was the continued need for harmonization of maternal adverse event following immunization (AEFI) research and surveillance efforts within developing and developed country contexts. We conducted a systematic review as a preliminary step in the development of standardized AEFI definitions for use in maternal and neonatal clinical trials, post-licensure surveillance, and other vaccine studies. We documented the current extent and nature of variability in AEFI definitions and adverse event reporting among 74 maternal immunization studies, which reported a total of 240 different types of adverse events. Forty-nine studies provided explicit AEFI case definitions describing 35 separate types of AEFIs. We identified variability in how AEFIs were determined to be present, in how AEFI definitions were applied, and in the ways that AEFIs were reported. Definitions for key maternal/neonatal AEFIs differed on four discrete attributes: overall level of detail, physiological and temporal boundaries and cut-offs, severity strata, and standards used. Our findings suggest that investigators may proactively address these inconsistencies through comprehensive and consistent reporting of AEFI definitions and outcomes in future publications. In addition, efforts to develop standardized AEFI definitions should generate definitions of sufficient detail and consistency of language to avoid the ambiguities we identified in reviewed articles, while remaining practically applicable given the constraints of low-resource contexts such as limited diagnostic capacity and high patient throughput.

Influenza virus infection in pregnancy: a review

BACKGROUND

Influenza virus infection is very common and a significant cause of morbidity and mortality in specific populations like pregnant women. Following the 2009 pandemic, several reports on the effects of influenza virus infection on maternal health and pregnancy outcome have been published. Also the safety and efficacy of antiviral treatment and vaccination of pregnant women have been studied. In this review, we have analyzed and summarized these data.

OBJECTIVE

To provide information on the influence of influenza virus infection during pregnancy on maternal health and pregnancy outcome and on the effect of treatment and vaccination.

DATA SOURCES

We have searched Medline, Embase and the Cochrane Library. We used influenza, influenz*, pregnancy and pregnan* as search terms.

STUDY SELECTION

In total, 294 reports were reviewed and judged according to the STROBE guidelines or CONSORT statement. In all, 100 studies, published between 1961 and 2015, were included.

RESULTS

Compared to the general population, pregnant women are more often hospitalized and admitted to an intensive care unit due to influenza virus infection. For hospitalized patients, increased rates of preterm birth and fetal/neonatal death are reported. Early treatment with oseltamivir is associated with a reduced risk of severe disease. Vaccination of pregnant women is safe and reduces maternal and neonatal morbidity.

CONCLUSIONS

There is level 2b evidence that maternal health and pregnancy outcome can be severely affected by influenza virus infection. Antiviral treatment may diminish these effects and vaccination protects pregnant women and neonates from infection (level of evidence 2b and 1b, respectively).

[Influenza and pregnancy]

Influenza is a respiratory disease caused by influenza viruses. The virus is responsible for pandemics by emergence of new viral strains, then for seasonal flu by antigenic drift. Seasonal flu is more frequent and severe in pregnant women, with increased risk of pneumonia and increased risk of hospitalization (but no increased death reported). Pandemic flu is more severe in pregnant women, with increased risk of pneumonia and increased mortality. Influenza vaccination is recommended for all women who are or will be pregnant (in any trimester) during influenza season. After closed contact with a flu case or in case of symptoms compatible with flu, early oseltamivir-based treatment (prophylactic in the first situation, curative in the latter one) is recommended, at any term of pregnancy. The occurrence of flu symptoms in a pregnant woman requires medical evaluation to confirm the diagnosis or identify any alternative infection requiring appropriate therapy like listeriosis, chorioamniotitis, pyelonephritis or viral primo-infection.

Development of a mother-child database for drug exposure and adverse event detection in the Military Health System

PURPOSE

The aim of this study was to develop a mother-child linked database consisting of all eligible active duty military personnel, retirees, and their dependents in order to conduct medication-related analyses to improve the safety and quality of care in the Military Health System (MHS).

METHODS

Eligible women of reproductive age with at least one pregnancy-related encounter between January 2005 and December 2013 receiving care in the MHS were included in the study population. Building on previously published algorithms, we used pregnancy-related diagnostic and procedure codes, parameterized temporal constraints, and data elements unique to the MHS to identify pregnancies ending in live births, stillbirth, spontaneous abortion, or ectopic pregnancy. Pregnancies ending in live births were matched to presumptive offspring using birth dates and family-based sponsorship identification. Antidepressant and antiepileptic use during pregnancy was evaluated using electronic pharmacy data.

RESULTS

Algorithms identified 755,232 women who experienced 1,099,648 complete pregnancies with both pregnancy care encounter and pregnancy outcome. Of the 924,320 live birth pregnancies, 827,753 (90.0%) were matched to offspring. Algorithms also identified 5,663 stillbirths, 11,358 ectopic pregnancies, and 169,665 spontaneous abortions. Among the matched singleton live birth pregnancies, 7.1% of mothers were dispensed an antidepressant at any point during pregnancy, usually a selective serotonin reuptake inhibitor, (75.3%), whereas 1.3% of mothers were dispensed an antiepileptic drug.

Influenza vaccination during pregnancy and its usefulness to mothers and their young infants

The current approach to protecting pregnant women from influenza infection and serious influenza-related complications is vaccination. It is, therefore, critical to evaluate the vaccine's safety, immunogenicity, and protection efficacy during pregnancy. However, because it is affected by previous influenza vaccination or infection, the efficacy of the seasonal trivalent inactivated influenza vaccine is difficult to evaluate in pregnant women. The A/H1N1pdm pandemic in 2009 provided us with the opportunity to evaluate the immunogenicity of the influenza vaccine unaffected by previous vaccinations or infections. Vaccination with inactivated influenza virus during pregnancy elicited neutralizing antibody titers that were sufficient and comparable to those of naturally infected individuals. Furthermore, post-pandemic surveys provided a wealth of definitive information on vaccine efficacy and safety. In addition, transplacental transfer of antibodies following vaccination protected newborn infants against influenza infection. With reports showing the effectiveness of influenza vaccine during pregnancy, it is suggested that influenza vaccination benefits both mothers and their young infants.

Monovalent H1N1 influenza vaccine safety in pregnant women, risks for acute adverse events

OBJECTIVE

To assess risks for acute adverse events and pregnancy complications in pregnant women following monovalent 2009 H1N1 inactivated influenza (MIV) vaccination.

METHODS

Within the Vaccine Safety Datalink, we compared rates of pre-specified medically attended events (MAE) occurring within 42 days of MIV vaccination to those occurring in matched cohorts that at the same gestational age were either unvaccinated or received seasonal trivalent inactivated influenza (TIV) vaccine. Using generalized estimating equation method, with a Poisson distribution and log link, we calculated adjusted incident rate ratios (AIRR).

RESULTS

Among 9349 women receiving MIV in any trimester, only one MAE occurred 0-3 days following MIV, an allergic reaction. No cases of Guillain-Barré syndrome, Bell's palsy, or transverse myelitis occurred 1-42 days after MIV. Compared to women receiving TIV and to unvaccinated women, risks for acute MAEs were not increased following MIV for any outcome. Hyperemesis was the most common adverse event in the MIV, TIV, and unvaccinated groups, occurring at a rate of about 4% over a 42-day period in all groups. Over a 42-day window, among all groups, incident gestational diabetes occurred at a rate of 3% and thrombocytopenia occurred at a rate of approximately 0.3%. Among women receiving MIV during pregnancy, increased risks for these and other less common obstetric events were not detected.

CONCLUSION

In this large cohort of pregnant women no acute safety signals were identified within 6 weeks of receipt of MIV.

Maternal vaccination: moving the science forward

BACKGROUND

Infections remain one of the leading causes of morbidity in pregnant women and newborns, with vaccine-preventable infections contributing significantly to the burden of disease. In the past decade, maternal vaccination has emerged as a promising public health strategy to prevent and combat maternal, fetal and neonatal infections. Despite a number of universally recommended maternal vaccines, the development and evaluation of safe and effective maternal vaccines and their wide acceptance are hampered by the lack of thorough understanding of the efficacy and safety in the pregnant women and the offspring.

METHODS

An outline was synthesized based on the current status and major gaps in the knowledge of maternal vaccination. A systematic literature search in PUBMED was undertaken using the key words in each section title of the outline to retrieve articles relevant to pregnancy. Articles cited were selected based on relevance and quality. On the basis of the reviewed information, a perspective on the future directions of maternal vaccination research was formulated.

RESULTS

Maternal vaccination can generate active immune protection in the mother and elicit systemic immunoglobulin G (IgG) and mucosal IgG, IgA and IgM responses to confer neonatal protection. The maternal immune system undergoes significant modulation during pregnancy, which influences responsiveness to vaccines. Significant gaps exist in our knowledge of the efficacy and safety of maternal vaccines, and no maternal vaccines against a large number of old and emerging pathogens are available. Public acceptance of maternal vaccination has been low.

CONCLUSIONS

To tackle the scientific challenges of maternal vaccination and to provide the public with informed vaccination choices, scientists and clinicians in different disciplines must work closely and have a mechanistic understanding of the systemic, reproductive and mammary mucosal immune responses to vaccines. The use of animal models should be coupled with human studies in an iterative manner for maternal vaccine experimentation, evaluation and optimization. Systems biology approaches should be adopted to improve the speed, accuracy and safety of maternal vaccine targeting.

Fetal death and preterm birth associated with maternal influenza vaccination: systematic review

BACKGROUND

Before 2012, few studies had addressed pregnancy outcomes following maternal influenza vaccination; however, the number of publications on this topic has increased recently.

OBJECTIVES

To review comparative studies evaluating fetal death or preterm birth associated with influenza vaccination during pregnancy.

SEARCH STRATEGY

We searched bibliographic databases from inception to April 2014.

SELECTION CRITERIA

Experimental or observational studies assessing the relationship between influenza vaccination during pregnancy and fetal death or preterm birth.

DATA COLLECTION AND ANALYSIS

Two reviewers independently abstracted data from studies meeting the inclusion criteria.

MAIN RESULTS

We included one randomised clinical trial and 26 observational studies. Meta-analyses were not considered appropriate because of high clinical and statistical heterogeneity. Three studies of fetal death at any gestational age reported adjusted effect estimates in the range 0.56-0.79, and four of five studies of fetal death at <20 weeks reported adjusted estimates between 0.89 and 1.23, all with confidence intervals including 1.0. Adjusted effect estimates for four of five studies of fetal death at ≥20 weeks ranged from 0.44 to 0.77 (two with confidence intervals not crossing 1.0), whereas a fifth reported a non-significant effect in the opposite direction. Among 19 studies of preterm birth, there was no strong evidence suggesting any increased risk, and meta-regression did not explain the moderate between-study heterogeneity (I(2) = 57%).

AUTHORS' CONCLUSIONS

Most studies reported no association between fetal death or preterm birth and influenza vaccination during pregnancy. Although several reported risk reductions, results may be biased by methodological shortcomings of observational studies of influenza vaccine effectiveness.

Influenza vaccination and fetal and neonatal outcomes

As pregnant women are considered a high-risk group for severe influenza illness, current recommendations advise vaccination of all pregnant women with inactivated influenza vaccine. Nevertheless, rates of maternal influenza vaccination have historically been low, possibly reflecting ongoing concerns about vaccine safety. Until recently, the majority of evidence concerning safety of influenza vaccination during pregnancy was limited to post-marketing pharmacovigilance studies; however, in the past 5 years, one randomized clinical trial and a number of observational studies reflecting seasonal trivalent inactivated influenza vaccines and monovalent H1N1 influenza vaccines have been published. This review summarizes the evidence pertaining to fetal and neonatal outcomes following influenza vaccination during pregnancy for comparative analytic studies published between 2008 and August 2013. Since the majority of these studies are observational in nature, issues related to study quality are also addressed.

Evaluation of safety of A/H1N1 pandemic vaccination during pregnancy: cohort study

OBJECTIVE

To assess the risk of maternal, fetal, and neonatal outcomes associated with the administration of an MF59 adjuvanted A/H1N1 vaccine during pregnancy.

DESIGN

Historical cohort study.

SETTING

Singleton pregnancies of the resident population of the Lombardy region of Italy.

PARTICIPANTS

All deliveries between 1 October 2009 and 30 September 2010. Data on exposure to A/H1N1 pandemic vaccine, pregnancy, and birth outcomes were retrieved from regional databases. Vaccinated and non-vaccinated women were compared in a propensity score matched analysis to estimate risks of adverse outcomes.

MAIN OUTCOME MEASURES

Main maternal outcomes included type of delivery, admission to intensive care unit, eclampsia, and gestational diabetes; fetal and neonatal outcomes included perinatal deaths, small for gestational age births, and congenital malformations.

RESULTS

Among the 86,171 eligible pregnancies, 6246 women were vaccinated (3615 (57.9%) in the third trimester and 2557 (40.9%) in the second trimester). No difference was observed in terms of spontaneous deliveries (adjusted odds ratio 1.02, 95% confidence interval 0.96 to 1.08) or admissions to intensive care units (0.95, 0.47 to 1.88), whereas a limited increase in the prevalence of gestational diabetes (1.26, 1.04 to 1.53) and eclampsia (1.19, 1.04 to 1.39) was seen in vaccinated women. Rates of fetal and neonatal outcomes were similar in vaccinated and non-vaccinated women. A slight increase in congenital malformations, although not statistically significant, was present in the exposed cohort (1.14, 0.99 to 1.31).

CONCLUSIONS

Our findings add relevant information about the safety of the MF59 adjuvanted A/H1N1 vaccine in pregnancy. Residual confounding may partly explain the increased risk of some maternal outcomes. Meta-analysis of published studies should be conducted to further clarify the risk of infrequent outcomes, such as specific congenital malformations.

2009 A/H1N1 influenza vaccination in pregnancy: uptake and pregnancy outcomes - a historical cohort study

OBJECTIVES

To describe the uptake of 2009 A/H1N1 influenza vaccination among pregnant women and determine if vaccination was associated with adverse pregnancy outcomes.

STUDY DESIGN

A historical cohort study was performed using booking, delivery suite and neonatal unit discharge records from the Coombe Women and Infants University Hospital, Dublin, Ireland. Singleton deliveries to women pregnant before (December 2008-September 2009) and during the pandemic (December 2009-September 2010) were included. Information on vaccination status and type of vaccine was collected on admission to the delivery suite. Logistic regression analyses were used to determine maternal characteristics associated with vaccination. Pregnancy outcomes were compared for vaccinated and unvaccinated women, with adjustment for differing maternal characteristics. Outcomes included vaccination status, preterm birth, size for gestational age, neonatal intensive care admission, congenital anomalies and perinatal death.

RESULTS

Of 6894 women pregnant during the pandemic, 2996 [43.5%] reported vaccination at delivery. In the early weeks of the vaccination programme rates of over 70% were achieved. Of those vaccinated, 246 [8.2%], 1709 [57.0%] and 1034 [34.5%] were vaccinated in the first, second and third trimesters respectively. Vaccination was less likely in younger age groups, those who were not in the professional/manager/employer socioeconomic group, women from Eastern Europe, Africa and Asia/Middle East, those who reported an unplanned pregnancy, women who booked late for antenatal care and recipients of publicly-funded obstetric care. Irish nationality was associated with reporting vaccination. There was no association between vaccination during pregnancy and adverse pregnancy outcomes. Women who were vaccinated were less likely to have a preterm delivery than unvaccinated women.

CONCLUSION

2009 A/H1N1 influenza vaccination uptake was influenced by maternal sociodemographic factors. High vaccination uptake can be achieved in a pandemic situation. Future public health campaigns should provide clear information on vaccination safety in pregnancy, ensure consistent vaccination recommendations from healthcare professionals and provide easy access to vaccination in order to optimise uptake rates in subgroups of the population who less likely to be vaccinated. There was no association between vaccination and adverse pregnancy outcomes.

Safety of influenza vaccination during pregnancy: a review of subsequent maternal obstetric events and findings from two recent cohort studies

Pregnant women and their infants are vulnerable to severe disease and secondary complications from influenza infection. For this reason, annual influenza vaccination is recommended for all pregnant women in the United States. Women frequently cite concerns about vaccine safety as a barrier to vaccination. This review describes the safety of inactivated influenza vaccination during pregnancy with a focus on maternal obstetric events, including hypertensive disorders, gestational diabetes, and chorioamnionitis. Included in the review are new findings from two studies which examined the safety of seasonal inactivated influenza vaccination during pregnancy. The first study enrolled 641 pregnant women during the 2010-2011 season and prospectively followed them until delivery or pregnancy termination. The second study enrolled 1616 pregnant women during the 2010-2011 influenza season, and followed the women and their infants for six months after delivery. No associations between inactivated influenza vaccination and gestational diabetes, gestational hypertension, preeclampsia/eclampsia, or chorioamnionitis were observed in either cohort. When considered as a whole, these studies should further reassure women and clinicians that influenza vaccination during pregnancy is safe for mothers.

Vaccines for preventing influenza in healthy adults

BACKGROUND

Different types of influenza vaccines are currently produced worldwide. Vaccination of pregnant women is recommended internationally, while healthy adults are targeted in North America.

OBJECTIVES

To identify, retrieve and assess all studies evaluating the effects (efficacy, effectiveness and harm) of vaccines against influenza in healthy adults, including pregnant women.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2013, Issue 2), MEDLINE (January 1966 to May 2013) and EMBASE (1990 to May 2013).

SELECTION CRITERIA

Randomised controlled trials (RCTs) or quasi-RCTs comparing influenza vaccines with placebo or no intervention in naturally occurring influenza in healthy individuals aged 16 to 65 years. We also included comparative studies assessing serious and rare harms.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed trial quality and extracted data.

MAIN RESULTS

We included 90 reports containing 116 data sets; among these 69 were clinical trials of over 70,000 people, 27 were comparative cohort studies (about eight million people) and 20 were case-control studies (nearly 25,000 people). We retrieved 23 reports of the effectiveness and safety of vaccine administration in pregnant women (about 1.6 million mother-child couples).The overall effectiveness of parenteral inactivated vaccine against influenza-like illness (ILI) is limited, corresponding to a number needed to vaccinate (NNV) of 40 (95% confidence interval (CI) 26 to 128). The overall efficacy of inactivated vaccines in preventing confirmed influenza has a NNV of 71 (95% CI 64 to 80). The difference between these two values depends on the different incidence of ILI and confirmed influenza among the study populations: 15.6% of unvaccinated participants versus 9.9% of vaccinated participants developed ILI symptoms, whilst only 2.4% and 1.1%, respectively, developed laboratory-confirmed influenza.No RCTs assessing vaccination in pregnant women were found. The only evidence available comes from observational studies with modest methodological quality. On this basis, vaccination shows very limited effects: NNV 92 (95% CI 63 to 201) against ILI in pregnant women and NNV 27 (95% CI 18 to 185) against laboratory-confirmed influenza in newborns from vaccinated women.Live aerosol vaccines have an overall effectiveness corresponding to a NNV 46 (95% CI 29 to 115).The performance of one-dose or two-dose whole virion pandemic vaccines was higher, showing a NNV of 16 (95% CI 14 to 20) against ILI and a NNV of 35 (95% CI 33 to 47) against influenza, while a limited impact on hospitalisation was found (NNV 94, 95% CI 70 to 1022).Vaccination had a modest effect on time off work and had no effect on hospital admissions or complication rates. Inactivated vaccines caused local harms. No evidence of association with serious adverse events was found, but the harms evidence base was limited.The overall risk of bias in the included trials is unclear because it was not possible to assess the real impact of bias.

AUTHORS' CONCLUSIONS

Influenza vaccines have a very modest effect in reducing influenza symptoms and working days lost in the general population, including pregnant women. No evidence of association between influenza vaccination and serious adverse events was found in the comparative studies considered in the review. This review includes 90 studies, 24 of which (26.7%) were funded totally or partially by industry. Out of the 48 RCTs, 17 were industry-funded (35.4%).

Pandemic A/H1N1 influenza vaccination during pregnancy: a comparative study using the EFEMERIS database

OBJECTIVE

To evaluate the risk of adverse pregnancy outcomes following A/H1N1 vaccination in pregnant women.

METHODS

This observational cohort study compared vaccinated and non-vaccinated pregnant women in EFEMERIS, a French prescription database including pregnant women. Women who ended their pregnancy in South Western France between October 21, 2009 and November 30, 2010 (the period of the French vaccination campaign) were included. Two non-vaccinated women were individually matched to each vaccinated woman by month and year of pregnancy onset. Conditional logistic regression and Cox proportional hazards regression were used to evaluate associations between each outcome (all-cause pregnancy loss, preterm delivery, small for gestational age (SGA) and neonatal pathology) and A/H1N1 vaccination during pregnancy.

RESULTS

1645 women of the 12,120 (13.6%) in the database who were administered A/H1N1 vaccine during pregnancy were compared to 3290 non-vaccinated women. Most were vaccinated in December 2009 (61%) with a non-adjuvanted vaccine (93%). The risks of pregnancy loss (adjusted HR=0.56; 95% CI=0.31-1.01), of preterm birth (adjusted HR=0.82; 95% CI=0.64-1.06), and of neonatal pathology (adjusted OR=0.70; 95% CI=0.49-1.02) did not differ between the vaccinated and the non-vaccinated groups. The rate of SGA was lower in the vaccinated group than in the non-vaccinated group (0.5% vs. 1.4%; adjusted OR=0.36; 95% CI=0.17-0.78).

CONCLUSION

There was no significant association between adverse pregnancy outcomes and vaccination with a non-adjuvanted A/H1N1 vaccine during pregnancy.