Effectiveness of maternal immunization with trivalent inactivated influenza vaccine in pregnant women and their infants

Effectiveness of Influenza Vaccination During Pregnancy Against Laboratory-Confirmed Seasonal Influenza Among Infants Under 6 Months of Age in Ontario, Canada

BACKGROUND

Randomized trials conducted in low- and middle-income settings demonstrated efficacy of influenza vaccination during pregnancy against influenza infection among infants <6 months of age. However, vaccine effectiveness (VE) estimates from settings with different population characteristics and influenza seasonality remain limited.

METHODS

We conducted a test-negative study in Ontario, Canada. All influenza virus tests among infants <6 months from 2010 to 2019 were identified and linked with health databases to ascertain information on maternal-infant dyads. VE was estimated from the odds ratio for influenza vaccination during pregnancy among cases versus controls, computed using logistic regression with adjustment for potential confounders.

RESULTS

Among 23 806 infants tested for influenza, 1783 (7.5%) were positive and 1708 (7.2%) were born to mothers vaccinated against influenza during pregnancy. VE against laboratory-confirmed infant influenza infection was 64% (95% confidence interval [CI], 50%-74%). VE was similar by trimester of vaccination (first/second, 66% [95% CI, 40%-80%]; third, 63% [95% CI, 46%-74%]), infant age at testing (0 to <2 months, 63% [95% CI, 46%-75%]; 2 to <6 months, 64% [95% CI, 36%-79%]), and gestational age at birth (≥37 weeks, 64% [95% CI, 50%-75%]; < 37 weeks, 61% [95% CI, 4%-86%]). VE against influenza hospitalization was 67% (95% CI, 50%-78%).

CONCLUSIONS

Influenza vaccination during pregnancy offers effective protection to infants <6 months, for whom vaccines are not currently available.

Influenza vaccination in pregnant women in Iceland 2010-2020 and the burden of influenza in pregnant women and their infants

INTRODUCTION

Influenza vaccinations are recommended in pregnancy to protect both the pregnant woman and the unborn baby. The aim of this study was to assess the influenza vaccine uptake among pregnant women in Iceland in ten influenza seasons and to estimate the influenza disease burden on pregnant women and their infants.

METHODS

This was a retrospective, descriptive study on influenza vaccine uptake among pregnant women and the burden of influenza and influenza-like illness (ILI) among pregnant women and their infants in ten influenza seasons. All women attending a 20-week ultrasound at Landspitali University Hospital in Reykjavik in August-April each influenza season 2010-2020 were included in the study. Data on influenza vaccinations and influenza/ILI diagnoses was collected from central national databases.

RESULTS

The influenza vaccine uptake increased from 6.2 % in 2011-2012 to 37.5 % in 2019-2020. The incidence rate of influenza/ILI among pregnant women ranged from 5.5 to 22.1/1000 person-years. The estimated vaccine effectiveness in the ten influenza seasons was 34-100 %. The incidence rate of influenza/ILI among infants < 12 months of age was 0-13.4/1000 person-years. Influenza vaccinations in pregnancy are protective against influenza/ILI in pregnant women (IRR 0.36, 95 % CI 0.22-0.58), infants in the season of vaccination (IRR 0.40, 95 % CI 0.17-0.97) and probably for infants < 6 months of age (IRR 0.51, 95 % CI 0.22-1.21).

CONCLUSIONS

Influenza vaccine coverage in pregnancy is suboptimal. Influenza vaccinations in pregnancy provide significant protection against influenza/ILI for pregnant women and infants in the season of vaccination. Initiatives to improve maternal vaccination coverage are needed.

Prenatal Maternal Immunization for Infant Protection: A Review of the Vaccines Recommended, Infant Immunity and Future Research Directions

Prenatal maternal immunization is an effective tool to protect mothers and infants from poor health outcomes due to infectious diseases. We provide an overview of the rationale for the use of prenatal vaccines, discuss the immunologic environment of the maternal-fetal interface including the impact of maternal vaccines prenatally and subsequently on the infant's immune response, and review vaccines currently recommended in pregnancy and landscape for the future of maternal vaccination. This review aims to provide an understanding of the recent history and progress made in the field and highlight the importance of continued research and development into new vaccines for pregnant populations.

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.

Seasonal Influenza Vaccine Effectiveness in Persons Aged 15-64 Years: A Systematic Review and Meta-Analysis

Influenza is a respiratory disease caused by the influenza virus, which is highly transmissible in humans. This paper presents a systematic review and meta-analysis of randomized controlled trials (RCTs) and test-negative designs (TNDs) to assess the vaccine effectiveness (VE) of seasonal influenza vaccines (SIVs) in humans aged 15 to 64 years. An electronic search to identify all relevant studies was performed. The outcome measure of interest was VE on laboratory-confirmed influenza (any strain). Quality assessment was performed using the Cochrane risk-of-bias tool for RCTs and the ROBINS-I tool for TNDs. The search identified a total of 2993 records, but only 123 studies from 73 papers were included in the meta-analysis. Of these studies, 9 were RCTs and 116 were TNDs. The pooled VE was 48% (95% CI: 42-54) for RCTs, 55.4% (95% CI: 43.2-64.9) when there was a match between the vaccine and most prevalent circulating strains and 39.3% (95% CI: 23.5-51.9) otherwise. The TNDs' adjusted VE was equal to 39.9% (95% CI: 31-48), 45.1 (95% CI: 38.7-50.8) when there was a match and 35.1 (95% CI: 29.0-40.7) otherwise. The match between strains included in the vaccine and strains in circulation is the most important factor in the VE. It increases by more than 25% when there is a match with the most prevalent circulating strains. The laboratorial method for confirmation of influenza is a possible source of bias when estimating VE.

Effectiveness of Influenza Vaccination of Pregnant Women for Prevention of Maternal and Early Infant Influenza-Associated Hospitalizations in South Africa: A Prospective Test-Negative Study

BACKGROUND

Influenza vaccination during pregnancy reduces influenza-associated illness in the women and their infants, but effectiveness estimates against influenza-associated hospitalization are limited and lacking from settings with high human immunodeficiency virus (HIV) infection prevalence. We assessed the effect of maternal vaccination in HIV-uninfected women and women with HIV in preventing influenza-associated hospitalizations in infants and the women.

METHODS

During 2015-2018, influenza vaccination campaigns targeting pregnant women were augmented at selected antenatal clinics; these were coupled with prospective hospital-based surveillance for acute respiratory or febrile illness in infants aged <6 months and cardiorespiratory illness among pregnant or postpartum women. Vaccine effectiveness (VE) was assessed using a test-negative case-control study.

RESULTS

Overall, 71 influenza-positive and 371 influenza-negative infants were included in the analysis; mothers of 26.8% of influenza-positive infants were vaccinated during pregnancy compared with 35.6% of influenza-negative infants, corresponding to an adjusted VE (aVE) of 29.0% (95% confidence interval [CI], -33.6% to 62.3%). When limited to vaccine-matched strains, aVE was 65.2% (95% CI, 11.7%-86.3%). For maternal hospitalizations, 56 influenza-positive and 345 influenza-negative women were included in the analysis, with 28.6% of influenza-positive women being vaccinated compared with 38.3% of influenza-negatives, for an aVE of 46.9% (95% CI, -2.8% to 72.5%). Analysis restricted to HIV-uninfected women resulted in 82.8% (95% CI, 40.7%-95.0%) aVE. No significant aVE (-32.5% [95% CI, -208.7% to 43.1%]) was detected among women with HIV.

CONCLUSIONS

Influenza vaccination during pregnancy prevented influenza-associated hospitalizations among young infants when infected with vaccine strains and among HIV-uninfected women.

SARS-CoV-2 tests, confirmed infections and COVID-19-related hospital admissions in children and young people: birth cohort study

BACKGROUND

There have been no population-based studies of SARS-CoV-2 testing, PCR-confirmed infections and COVID-19-related hospital admissions across the full paediatric age range. We examine the epidemiology of SARS-CoV-2 in children and young people (CYP) aged <23 years.

METHODS

We used a birth cohort of all children born in Scotland since 1997, constructed via linkage between vital statistics, hospital records and SARS-CoV-2 surveillance data. We calculated risks of tests and PCR-confirmed infections per 1000 CYP-years between August and December 2020, and COVID-19-related hospital admissions per 100 000 CYP-years between February and December 2020. We used Poisson and Cox proportional hazards regression models to determine risk factors.

RESULTS

Among the 1 226 855 CYP in the cohort, there were 378 402 tests (a rate of 770.8/1000 CYP-years (95% CI 768.4 to 773.3)), 19 005 PCR-confirmed infections (179.4/1000 CYP-years (176.9 to 182.0)) and 346 admissions (29.4/100 000 CYP-years (26.3 to 32.8)). Infants had the highest COVID-19-related admission rates. The presence of chronic conditions, particularly multiple types of conditions, was strongly associated with COVID-19-related admissions across all ages. Overall, 49% of admitted CYP had at least one chronic condition recorded.

CONCLUSIONS

Infants and CYP with chronic conditions are at highest risk of admission with COVID-19. Half of admitted CYP had chronic conditions. Studies examining COVID-19 vaccine effectiveness among children with chronic conditions and whether maternal vaccine during pregnancy prevents COVID-19 admissions in infants are urgently needed.

Maternal Vaccination and Risk of Hospitalization for Covid-19 among Infants

BACKGROUND

Infants younger than 6 months of age are at high risk for complications of coronavirus disease 2019 (Covid-19) and are not eligible for vaccination. Transplacental transfer of antibodies against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) after maternal Covid-19 vaccination may confer protection against Covid-19 in infants.

METHODS

We used a case-control test-negative design to assess the effectiveness of maternal vaccination during pregnancy against hospitalization for Covid-19 among infants younger than 6 months of age. Between July 1, 2021, and March 8, 2022, we enrolled infants hospitalized for Covid-19 (case infants) and infants hospitalized without Covid-19 (control infants) at 30 hospitals in 22 states. We estimated vaccine effectiveness by comparing the odds of full maternal vaccination (two doses of mRNA vaccine) among case infants and control infants during circulation of the B.1.617.2 (delta) variant (July 1, 2021, to December 18, 2021) and the B.1.1.259 (omicron) variant (December 19, 2021, to March 8, 2022).

RESULTS

A total of 537 case infants (181 of whom had been admitted to a hospital during the delta period and 356 during the omicron period; median age, 2 months) and 512 control infants were enrolled and included in the analyses; 16% of the case infants and 29% of the control infants had been born to mothers who had been fully vaccinated against Covid-19 during pregnancy. Among the case infants, 113 (21%) received intensive care (64 [12%] received mechanical ventilation or vasoactive infusions). Two case infants died from Covid-19; neither infant's mother had been vaccinated during pregnancy. The effectiveness of maternal vaccination against hospitalization for Covid-19 among infants was 52% (95% confidence interval [CI], 33 to 65) overall, 80% (95% CI, 60 to 90) during the delta period, and 38% (95% CI, 8 to 58) during the omicron period. Effectiveness was 69% (95% CI, 50 to 80) when maternal vaccination occurred after 20 weeks of pregnancy and 38% (95% CI, 3 to 60) during the first 20 weeks of pregnancy.

CONCLUSIONS

Maternal vaccination with two doses of mRNA vaccine was associated with a reduced risk of hospitalization for Covid-19, including for critical illness, among infants younger than 6 months of age. (Funded by the Centers for Disease Control and Prevention.).

Trends of influenza vaccination coverage in pregnant women: a ten-year analysis from a French healthcare database

Pregnant women have a high risk of severe influenza, associated with obstetrical complications. The World Health Organization (WHO) has recommended influenza vaccination for all pregnant women since 2012. The vaccination coverage remains low worldwide, and in Europe, due to a lack of proposition from the health care providers, and a high refusal rate from the women. The primary aim of this study was to estimate the influenza vaccination coverage (IVC) in a population of pregnant women in France, and to analyse its evolution from 2009 to 2018. The secondary objective was to describe the vaccinated population and to find determinants associated with the vaccination. This retrospective cohort study is based on the EGB French health care database, a representative sample of the French population containing data from the health insurance system. All pregnant women who delivered medically or spontaneously over the 2009–2018 period were included. In the 2009–2018 period, only 1.2% pregnant women were vaccinated against influenza (n = 875/72,207; 95% CI 1.14–1.30). The IVC slightly increased after the 2012 WHO recommendation, from 0.33 to 1.79% (p < 0.001) but remained extremely low (4.1% in 2018). Women younger than 25 years old had a low coverage (0.6%) whereas women over 35 years old were more likely to get the influenza vaccine (1.7%; OR: 2.82, 95% CI 2.14–3.71). The vaccination behavior was not influenced by multifetal pregnancy or parity, but socio-economically deprived women were less likely to be vaccinated (OR: 0.81, 95% CI: 0.67–0.98). Women with pre-existing medical conditions had an overall higher vaccination rate (2.5%; OR: 2.32, 95% CI: 1.94–2.77). The vaccine was mainly prescribed by family physicians (58%). Influenza vaccination in pregnant women in France remains very low, particularly in younger, healthy women, and measures such as information campaigns towards pregnant women and studies of the knowledge, attitudes, and practices of the health care professionals need to be undertaken to improve the coverage.

Safety, Immunogenicity, Efficacy and Effectiveness of Inactivated Influenza Vaccines in Healthy Pregnant Women and Children Under 5 Years: An Evidence-Based Clinical Review

Annual influenza vaccination is often recommended for pregnant women and young children to reduce the risk of severe influenza. However, most studies investigating the safety, immunogenicity, and efficacy or effectiveness of influenza vaccines are conducted in healthy adults. In this evidence-based clinical review, we provide an update on the safety profile, immunogenicity, and efficacy/effectiveness of inactivated influenza vaccines (IIVs) in healthy pregnant women and children <5 years old. Six electronic databases were searched until May 27, 2021. We identified 3,731 articles, of which 93 met the eligibility criteria and were included. The IIVs were generally well tolerated in pregnant women and young children, with low frequencies of adverse events following IIV administration; however, continuous vaccine safety monitoring systems are necessary to detect rare adverse events. IIVs generated good antibody responses, and the seroprotection rates after IIVs were moderate to high in pregnant women (range = 65%-96%) and young children (range = 50%-100%), varying between the different influenza types/subtypes and seasons. Studies show vaccine efficacy/effectiveness values of 50%-70% in pregnant women and 20%-90% in young children against lab-confirmed influenza, although the efficacy/effectiveness depended on the study design, host factors, vaccine type, manufacturing practices, and the antigenic match/mismatch between the influenza vaccine strains and the circulating strains. Current evidence suggests that the benefits of IIVs far outweigh the potential risks and that IIVs should be recommended for pregnant women and young children.

Maternal Vaccination and Infant Influenza and Pertussis

BACKGROUND AND OBJECTIVES

Infant influenza and pertussis disease causes considerable morbidity and mortality worldwide. We examined the effectiveness of maternal influenza and pertussis vaccines in preventing these diseases in infants.

METHODS

This inception cohort study comprised women whose pregnancies ended between September 1, 2015, and December 31, 2017, in Victoria, Australia. Maternal vaccination status was sourced from the Victorian Perinatal Data Collection and linked to 5 data sets to ascertain infant outcomes and vaccination. The primary outcome of interest was laboratory-confirmed influenza or pertussis disease in infants aged <2 months, 2 to <6 months, and <6 months combined. Secondary outcomes included infant hospitalization (emergency presentation or admission) and death. Risk ratios and 95% confidence intervals (CIs) were estimated by Poisson regression. Vaccine effectiveness (VE) was estimated as (1 minus the risk ratio) x 100%.

RESULTS

Among 186 962 pregnant women, 85 830 (45.9%) and 128 060 (68.5%) were vaccinated against influenza and pertussis, respectively. There were 175 and 51 infants with laboratory-confirmed influenza and pertussis disease, respectively. Influenza VE was 56.1% (95% CI, 23.3% to 74.9%) for infants aged <2 months and 35.7% (2.2% to 57.7%) for infants aged 2 to <6 months. Pertussis VE was 80.1% (95% CI, 37.1% to 93.7%) for infants aged <2 months and 31.8% (95% CI, -39.1% to 66.6%) for infants aged 2 to <6 months.

CONCLUSIONS

Our study provides evidence of the direct effectiveness of maternal influenza and pertussis vaccination in preventing these diseases in infants aged <2 months. The findings strengthen the importance of maternal vaccination to prevent these diseases in infants.

Vaccination as a preventative measure contributing to immune fitness

The primary goal of vaccination is the prevention of pathogen-specific infection. The indirect consequences may include maintenance of homeostasis through prevention of infection-induced complications; trained immunity that re-programs innate cells to respond more efficiently to later, unrelated threats; slowing or reversing immune senescence by altering the epigenetic clock, and leveraging the pool of memory B and T cells to improve responses to new infections. Vaccines may exploit the plasticity of the immune system to drive longer-term immune responses that promote health at a broader level than just the prevention of single, specific infections. In this perspective, we discuss the concept of “immune fitness” and how to potentially build a resilient immune system that could contribute to better health. We argue that vaccines may contribute positively to immune fitness in ways that are only beginning to be understood, and that life-course vaccination is a fundamental tool for achieving healthy aging.

Methodologic approaches in studies using real-world data (RWD) to measure pediatric safety and effectiveness of vaccines administered to pregnant women: A scoping review

OBJECTIVE

This scoping review mapped studies using real-world data (RWD) to measure pediatric safety and effectiveness of vaccines administered to pregnant women.

INTRODUCTION

In the US, two vaccines are recommended for all pregnant women to prevent illness in the infant: inactivated influenza vaccine (recommended since 2004), and the combined tetanus-diphtheria-acellular pertussis (Tdap) vaccine (recommended since 2013). This scoping review maps the studies conducted to date that address questions about pediatric safety and effectiveness of vaccines administered during pregnancy and provides a knowledge base for evaluating the use of RWD to study this issue.

METHODS

The scoping review was conducted following a published protocol. Methods included an electronic search of PubMed and Embase, screening of titles and abstracts by two reviewers, and double extraction of data for summary and synthesis. Studies that reported on pregnant women and the effectiveness or safety outcomes in their infants were included.

RESULTS

Forty-eight studies met the inclusion criteria of the scoping review protocol using RWD to assess safety or effectiveness of influenza or pertussis vaccinations administered to pregnant women with respect to pregnancy, infant or child outcomes. Detailed information about data sources, linkage of maternal and infant data, and operational definitions for gestational age were largely absent from the majority of studies raising concerns about reproducibility and validity of study findings.

CONCLUSIONS

A body of literature is available from which to plan and design future studies of vaccination in pregnant women using RWD. This is of intense importance as new vaccines, such as those for COVID-19, become available to the general population via approval or authorization without inclusion of pregnant women in the clinical trials.

Efficacy and safety of influenza vaccination during pregnancy: realizing the potential of maternal influenza immunization

Introduction: Pregnant women are at higher risk of severe complications following influenza infection compared to the general population. Influenza vaccination during pregnancy can offer direct protection to pregnant women and passive immunity to infants up to 6 months of age via maternal antibodies. Pregnant women are a high priority group for influenza immunization.Areas covered: This review provides an overview of the basis for recommending influenza vaccine to pregnant women, current immunization policies, the evidence supporting the safety and effectiveness of maternal vaccination, and future research needed. We conducted a search of PubMed for articles describing the safety or efficacy of influenza vaccines administered during pregnancy. Published articles from inception to 17 November 2020 were reviewed.Expert opinion: Experimental and observational evidence support the efficacy, effectiveness and safety of influenza immunization during pregnancy. These data support the continued provision of inactivated influenza vaccine to pregnant women, as recommended by global immunization policies. To achieve success with maternal influenza immunization programs, further work is needed to inform policy development in low- and middle-income settings and implementation and promotion in high-income settings.

Vaccination of pregnant women against influenza: what is the optimal timing?

Pregnant women and young infants are at increased risk for severe influenza and its complications. Influenza vaccination during pregnancy is increasingly implemented as a strategy aiming to protect the pregnant woman, the fetus and the young infant. In clinical practice, the achievement of satisfactory protection for the pregnant woman without compromising the protection of her infant during the first months of life remains a challenge. Determinants that are implicated in the optimal timing of influenza vaccination in pregnancy include influenza season, trimester of pregnancy, maternal host factors and infant factors. This article addresses influenza vaccination in pregnancy and presents recent published evidence on issues that affect the optimization of the timing of maternal vaccination.

Cost-effectiveness of influenza vaccination during pregnancy

OBJECTIVE

To assess the cost-effectiveness of influenza vaccination for all pregnant patients in the United States.

METHODS

We designed a cost-effectiveness model to compare outcomes and costs in pregnant patients who received the inactivated, trivalent influenza vaccine to those who did not. We used a theoretical cohort of 4 million patients, the number of individuals giving birth in the United States per year. We assumed that H1N1 and A or B type influenza were of equal incidence based on seasonal variation from the past ten years. Our outcomes include acquiring H1N1, acquiring A or B type influenza, maternal death, stillbirth, infant death, preterm birth, and cerebral palsy in addition to cost and quality-adjusted life years (QALYs). Probabilities were derived from the literature and QALYs generated at a discount rate of 3%. Sensitivity analyses were performed to assess the robustness of our model.

RESULTS

In our theoretical cohort of 4 million pregnant patients, the influenza vaccination strategy was associated with 1632 fewer stillbirths (24,332 in the vaccine strategy vs. 25,964 in the no vaccine strategy), 120 fewer maternal deaths (284 vs. 404), 340 fewer infant deaths (5608 vs. 5948), 32,856 fewer preterm births (403,896 vs. 436,752), and 641 fewer cases of moderate cerebral palsy (12,388 vs. 13,029). Additionally, the vaccination strategy corresponded to savings of $3.7 billion ($63.3 billion vs. $67.0 billion) and increased QALYs of 81,696 (226,852,076 vs 226,770,380). Therefore, it was considered a dominant strategy. Univariate sensitivity analysis demonstrated that the vaccine is cost saving until vaccine cost passes $900, far above the current cost of $12.16. In addition, we used sensitivity analysis to vary seasonal proportions of H1N1 to A or B type influenza. The vaccine was cost saving and increased QALYs for any proportion of H1N1 to A or B type influenza including when H1N1 was absent.

CONCLUSION

We demonstrate that in a cohort of 4 million patients, the influenza vaccine may save $3.7 billion per year, improve maternal and infant outcomes, and reduce morbidity and mortality. Our study provides further evidence that providers should strongly recommend that pregnant patients receive their annual influenza vaccine.

Individual and Neighborhood Factors Associated With Failure to Vaccinate Against Influenza During Pregnancy

Uptake of influenza vaccine among pregnant women remains low. We investigated whether unvaccinated pregnant women were clustered geographically and determined factors associated with failure to vaccinate using spatial and multivariate logistic regression analyses. Pregnant women who were members of Kaiser Permanente Northern California in 2015 or 2016 were included in the study. More than half (53%) of the 77,607 included pregnant women were unvaccinated. Spatial analysis identified 5 clusters with a high prevalence of unvaccinated pregnant women. The proportion of unvaccinated women ranged from 57% to 75% within clusters as compared with 51% outside clusters. In covariate-adjusted analyses, residence in a cluster was associated with a 41% increase in the odds of being unvaccinated (odds ratio (OR) = 1.41, 95% confidence interval (CI): 1.36, 1.46). The odds of being unvaccinated were greater for Black women (OR = 1.58, 95% CI: 1.49, 1.69), Hispanic women (OR = 1.15, 95% CI: 1.05, 1.25), women with subsidized health insurance (OR = 1.18, 95% CI: 1.11, 1.24), women with fewer than 5 prenatal-care visits (OR = 1.85, 95% CI: 1.60, 2.16), and neighborhoods with a high deprivation index (fourth quartile vs. first: OR = 1.14, 95% CI: 1.07, 1.21). In conclusion, unvaccinated pregnant women were clustered geographically and by key sociodemographic factors. These findings suggest that interventions to increase influenza vaccine coverage among pregnant women are needed, particularly in vulnerable populations.

The effectiveness of influenza vaccination in pregnancy in relation to child health outcomes: Systematic review and meta-analysis

OBJECTIVES

To determine the effectiveness of influenza vaccination during pregnancy on child health outcomes.

DESIGN

Systematic review/meta-analysis.

DATA SOURCES

Clinical Trials.gov, Cochrane Library, EMBASE, Medline, Medline in process, PubMed and Web of Science, from 1st January 1996 to 29th June 2018. An updated Medline search was performed 30th June 2018 to 31st October 2019.

METHODS

Randomised controlled trials (RCTs) and observational studies reporting health outcomes of infants and children born to women who received inactivated influenza vaccine during pregnancy. The primary outcome was infant laboratory confirmed influenza (LCI). Secondary outcomes included influenza-like illness (ILI), other respiratory illnesses, primary care, clinic visit or hospitalisations due to influenza illness and long-term respiratory childhood outcomes.

RESULTS

19 studies were included; 15 observational studies and 4 primary RCTs with an additional 3 papers reporting secondary outcomes of these RCTs. In a random effects meta-analysis of 2 RCTs including 5742 participants, maternal influenza vaccination was associated with an overall reduction of LCI in infants of 34% (95% confidence interval 15-50%). However, there was no effect of maternal influenza vaccination on ILI in infants ≤6 months old. Two RCTs were excluded from the meta-analysis for the outcome of LCI in infants (different controls used). Both of these studies showed a protective effect for infants from LCI, with a vaccine efficacy of up to 70%. Overall observational studies showed an inverse (protective) association between maternal influenza vaccination and infant LCI, hospitalisation and clinic visits due to LCI or ILI in infants and other respiratory illness in infants ≤6 months old.

CONCLUSIONS

This systematic review supports maternal influenza vaccination as a strategy to reduce LCI and influenza-related hospitalisations in young infants. Communicating these benefits to pregnant women may support their decision to accept influenza vaccination in pregnancy and increase vaccine coverage in pregnant women.

REGISTRATION

PROSPERO CRD42018102776.

Vaccinating pregnant women against influenza needs to be a priority for all countries: An expert commentary

BACKGROUND

In 2012, the World Health Organization recommended influenza vaccination for all pregnant women worldwide and the prioritisation of pregnant women in national influenza vaccination programmes. Nevertheless, vaccination rates in pregnant women often remain much lower than national targets.

OBJECTIVES

To assess the benefits and risks associated with influenza infection and vaccination during pregnancy, and to consider obstacles that work against influenza vaccine uptake during pregnancy.

RESULTS

There is strong evidence that maternal and foetal outcomes can be compromised if women develop influenza infections during pregnancy. Influenza vaccines have been administered to millions of pregnant women and have demonstrated benefits in terms of disease prevention in mothers and their infants. There is a consensus amongst several recommending authorities that influenza vaccines may be safely administered during all stages of pregnancy. Healthcare professionals are recognised as the most important influencers of vaccine uptake, being well placed to recommend vaccination and directly address safety concerns.

CONCLUSIONS

Despite data supporting the value of influenza vaccination during pregnancy, vaccine uptake remains low globally. Low uptake appears to be largely due to ineffective communication with pregnant women about the risks and benefits of influenza vaccination. A graphical abstract is available online.