Optimal timing of influenza vaccine during pregnancy: A systematic review and meta-analysis

Maternal Immunizations: Past, Present, and Future

Maternal vaccines during pregnancy offer crucial protection against infections for both the pregnant person and their newborn. Vaccines against influenza, pertussis, coronavirus disease 2019, and respiratory syncytial virus are routinely recommended by the Centers for Disease Control and Prevention to safeguard pregnant women and their infants from potentially severe complications. Administering these vaccines during pregnancy helps transfer protective antibodies from the mother to the baby, enhancing immunity during the vulnerable early months of life. Extensive research supports the safety and efficacy of maternal vaccines, with numerous studies demonstrating their protective benefits for both pregnant people and newborns.

From Womb to World: Exploring the Immunological Connections between Mother and Child

Mother and child are immunologically interconnected by mechanisms that we are only beginning to understand. During pregnancy, multiple molecular and cellular factors of maternal origin are transferred across the placenta and influence the development and function of the fetal and newborn immune system. Altered maternal immune states arising from pregnancy-associated infections or immunizations have the potential to program offspring immune function in ways that may have long-term health consequences. In this study, we review current literature on the impact of prenatal infection and vaccination on the developing immune system, highlight knowledge gaps, and look to the horizon to envision maternal interventions that could benefit both the mother and her child.

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.

Maternal hybrid immunity and risk of infant COVID-19 hospitalizations: national case-control study in Israel

Hybrid immunity, acquired through vaccination followed or preceded by a COVID-19 infection, elicits robust antibody augmentation. We hypothesize that maternal hybrid immunity will provide greater infant protection than other forms of COVID-19 immunity in the first 6 months of life. We conducted a case-control study in Israel, enrolling 661 infants up to 6 months of age, hospitalized with COVID-19 (cases) and 59,460 age-matched non-hospitalized infants (controls) between August 24, 2021, and March 15, 2022. Infants were grouped by maternal immunity status at delivery: Naïve (never vaccinated or tested positive, reference group), Hybrid-immunity (vaccinated and tested positive), Natural-immunity (tested positive before or during the study period), Full-vaccination (two-shot regimen plus 1 booster), and Partial-vaccination (less than full three shot regimen). Applying Cox proportional hazards models to estimate the hazard ratios, which was then converted to percent vaccine effectiveness, and using the Naïve group as the reference, maternal hybrid-immunity provided the highest protection (84% [95% CI 75-90]), followed by full-vaccination (66% [95% CI 56-74]), natural-immunity (56% [95% CI 39-68]), and partial-vaccination (29% [95% CI 15-41]). Maternal hybrid-immunity was associated with a reduced risk of infant hospitalization for Covid-19, as compared to natural-immunity, regardless of exposure timing or sequence. These findings emphasize the benefits of vaccinating previously infected individuals during pregnancy to reduce COVID-19 hospitalizations in early infancy.

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.

The protective role of maternal genetic immunization on maternal-fetal health and welfare

Pregnancy is a critical period associated with alterations in physiologic, biologic, and immunologic processes, which can affect maternal-fetal health through development of several infectious diseases. At birth, neonates have an immature immune system that makes them more susceptible to severe viral infections and diseases. For this reason, different maternal nutritional and immunization interventions have been used to improve the immune and health status of the mother and her neonate through passive immunity. Here, we reviewed the protective role of maternal immunization with different types of vaccines, especially genetic vaccines, during pregnancy in maternal-fetal health, immune response, colostrum quality, immune response, and anti-oxidative status. For this purpose, we have used different scientific databases (PubMed and Google Scholar) and other official web pages. We customized the search period range from the year 2000 to 2023 using the key words "maternal immunization" OR "gestation period/pregnancy" OR "genetic vaccination" OR "maternal-fetal health" OR "micronutrients" OR "neonatal immunity" "oxidative stress" OR "colostrum quality". The evidence demonstrated that inactivated or killed vaccines produced significant immune protection in the mother and fetus. Furthermore, most recent studies have suggested that the use of genetic vaccines (mRNA and DNA) during pregnancy is efficient at triggering the immune response in mother and neonate without the risk of undesired pregnancy outcomes. However, factors such as maternal redox balance, nutritional status, and the timing of immunization play essential roles in regulating immune response inflammatory status, antioxidant capacity, and the welfare of both the pregnant mother and her newborn.

Are maternal vaccines effective and safe for mothers and infants? A systematic review and meta-analysis of randomised controlled trials

INTRODUCTION

Maternal vaccination is a promising strategy to reduce the burden of vaccine-preventable diseases for mothers and infants. We aimed to provide an up-to-date overview of the efficacy and safety of all available maternal vaccines.

METHODS

We searched PubMed, Embase, CENTRAL and ClinicalTrials.gov on 1 February 2022, for phase III and IV randomised controlled trials (RCTs) that compared maternal vaccination against any pathogen with placebo or no vaccination. Primary outcomes were laboratory-confirmed or clinically confirmed disease in mothers and infants. Secondary safety outcomes included intrauterine growth restriction, stillbirth, maternal death, preterm birth, congenital malformations and infant death. Random effects meta-analysis were used to calculate pooled risk ratio's (RR). Quality appraisal was performed using the Grading of Recommendations, Assessment, Development and Evaluation (GRADE).

RESULTS

Six RCTs on four maternal vaccines, influenza, tetanus, diphtheria and pertussis (Tdap), pneumococcal and respiratory syncytial virus (RSV) were eligible. The overall risk of bias and certainty of evidence varied from low to high. Maternal influenza vaccination significantly reduced the number of laboratory-confirmed influenza cases (RR 0.58, 95% CI 0.42 to 0.79, event rate 57 vs 98, 2 RCTs, n=6003, I2=0%), and clinically confirmed influenza cases in mothers (RR 0.88, 95% CI 0.78 to 0.99, event rate 418 vs 472, 2 RCTs, n=6003, I2=0%), and laboratory-confirmed influenza in infants (RR 0.66, 95% CI 0.52 to 0.85, event rate 98 vs 148, 2 RCTs, n=5883, I2=0%), although this was not significant for clinically confirmed influenza in infants (RR 0.99, 95% CI 0.94 to 1.05, event rate 1371 vs 1378, 2 RCTs, n=5883, I2=0%). No efficacy data were available on maternal Tdap vaccination. Maternal pneumococcal vaccination did not reduce laboratory-confirmed and clinically confirmed middle ear disease (RR 0.49, 95% CI 0.24 to 1.02, event rate 9 vs 18, 1 RCT, n=133 and RR 0.88 95% CI 0.69 to 1.12, event rate 42 vs 47, 1 RCT, n=133, respectively), and clinically confirmed lower-respiratory tract infection (LRTI) (RR 1.08, 95% CI 0.82 to 1.43, event rate 18 vs 34, 1 RCT, n=70) in infants. Maternal RSV vaccination did not reduce laboratory-confirmed RSV LRTI in infants (RR 0.75, 95% CI 0.56 to 1.01, event rate 103 vs 71, 1 RCT, n=4527). There was no evidence of a significant effect of any of the maternal vaccines on the reported safety outcomes.

CONCLUSIONS

The few RCTs with low event rates suggest that, depending on the type of maternal vaccine, the vaccine might effectively prevent disease and within its size does not show safety concerns in mothers and infants.

PROSPERO REGISTRATION NUMBER

CRD42021235115.

Influenza-associated respiratory illness among five cohorts of pregnant women and their young infants (0-6 months), Bangladesh, 2013-2017

Background

Pregnant women with their infants are considered at higher risk for influenza-associated complications, and the World Health Organization (WHO) recommends influenza vaccination during pregnancy to protect them, including their infants (0-6 months). There are limited data on the influenza burden among pregnant women and their infants (0-6 months), and there are no routine influenza vaccinations in Bangladesh.

Methods

Five annual cohorts (2013-2017) of pregnant women were enrolled from the eight sub-districts of Bangladesh before the influenza season (May-September); they were contacted weekly to identify new onset of influenza-like illness (ILI) (subjective or measured fever and cough) and acute respiratory illness (ARI) (at least two of these symptoms: cough, rhinorrhea, or difficulty in breathing) among their infants from birth to 6 months of age. We collected nasopharyngeal swabs from ILI and ARI cases, tested by real-time reverse transcription polymerase chain reaction (rRT-PCR) for influenza virus (including types and subtypes) and estimated influenza incidence (95% CI)/10000 pregnant women-months or infant-months, respectively.

Results

We enrolled 9020 pregnant women, followed for 26,709 pregnancy-months, and detected 1241 ILI episodes. We also followed 8963 infants for 51,518 infant-months and identified 5116 ARI episodes. Influenza positivity was 23% for ILI and 3% for ARI cases. The overall incidence (2013-2017) of influenza among pregnant women was 158.5/10000 pregnant women-months (95% CI: 141.4-177.6) and that among infants was 21.9/10000 infant-months (95% CI: 18.2-26.5).

Conclusions

Although the data was collected more than 5 years ago, as the only baseline data, our findings illustrate evidence of influenza burden among pregnant women and infants (0-6 months), which may support preventive policy decisions in Bangladesh.

Maternal influenza vaccination preferentially boosts hemagglutinin stem-specific antibody resulting in efficient transplacental transfer of stem-specific IgG

OBJECTIVE

The objective of this study was to evaluate hemagglutinin stem-specific antibody response to the influenza vaccine during pregnancy and its transfer to the infant.

METHODS

The authors assessed antibody titers among maternal participants and their paired neonate's cord blood (CB) using enzyme-linked immunoassay. Fifteen pregnant participants pre-2019 and post-2019 seasonal influenza vaccine were compared with 18 prenatally vaccinated participants with paired neonatal CB samples. Total IgG and IgG subclass titers specific for whole vaccine antigens versus recombinant hemagglutinin stem-specific antigen were compared using Wilcoxon exact test.

RESULTS

Hemagglutinin stem-specific IgG was boosted more robustly than whole vaccine titers when comparing postvaccine versus prevaccine log2 IgG ratios (P = 0.04). Hemagglutinin stem-specific IgG titers were boosted postvaccination (prevaccine: 14.5 [95% confidence interval, 13.8-15.2] vs. postvaccine: 16 [95% confidence interval, 15.2-16.8], P = 0.004). While IgG to whole vaccine was similar in neonatal CB and maternal plasma (P = 0.09), hemagglutinin stem-specific IgG concentrated in CB (P = 0.002), which was dominated by IgG1 subclass (analysis of variance P < 0.05).

CONCLUSION

These data demonstrate the ability of pregnant women to generate a more robust antibody response to the stem region compared with the head region of hemagglutinin with transplacental transfer of IgG.

Impact of maternal SARS-CoV-2 booster vaccination on blood and breastmilk antibodies

Maternal COVID-19 vaccination could protect infants who are ineligible for vaccine through antibody transfer during pregnancy and lactation. We measured the quantity and durability of SARS-CoV-2 antibodies in human milk and infant blood before and after maternal booster vaccination. Prospective cohort of lactating women immunized with primary and booster COVID-19 vaccines during pregnancy or lactation and their infants. Milk and blood samples from October 2021 to April 2022 were included. Anti-nucleoprotein (NP) and anti-receptor binding domain (RBD) IgG and IgA in maternal milk and maternal and infant blood were measured and compared longitudinally after maternal booster vaccine. Forty-five lactating women and their infants provided samples. 58% of women were anti-NP negative and 42% were positive on their first blood sample prior to booster vaccine. Anti-RBD IgG and IgA in milk remained significantly increased through 120-170 days after booster vaccine and did not differ by maternal NP status. Anti-RBD IgG and IgA did not increase in infant blood after maternal booster. Of infants born to women vaccinated in pregnancy, 74% still had positive serum anti-RBD IgG measured on average 5 months after delivery. Infant to maternal IgG ratio was highest for infants exposed to maternal primary vaccine during the second trimester compared to third trimester (0.85 versus 0.29; p<0.001). Maternal COVID-19 primary and booster vaccine resulted in robust and long-lasting transplacental and milk antibodies. These antibodies may provide important protection against SARS-CoV-2 during the first six months of life.

Optimising the timing of whooping cough immunisation in mums (OpTIMUM) through investigating pertussis vaccination in pregnancy: an open-label, equivalence, randomised controlled trial

BACKGROUND

Pertussis vaccination in pregnancy is recommended in many countries to provide protection to young infants. The best timing for this vaccination is uncertain. In the UK, vaccination is recommended between 16 weeks and 32 weeks of gestation. In this trial we aimed to investigate the equivalence of three time periods for pertussis vaccination in pregnancy.

METHODS

In this open-label, equivalence, randomised controlled trial to investigate equivalence of different time windows for pertussis vaccination in pregnancy, participants were randomly assigned (1:1:1 ratio) to receive a pertussis-containing vaccine (Boostrix-inactivated poliovirus vaccine) in one of three gestational age groups, comprising group 1 (≤23 weeks + 6 days), group 2 (24-27 weeks + 6 days), and group 3 (28-31 weeks + 6 days) using a computer-generated randomisation list. The primary outcome was concentration of pertussis-specific antibodies in the infant born at term at birth. Maternal blood sampling was done before and 2 weeks after vaccination and at delivery, together with a cord sample, and an infant sample was collected at least 4 weeks after primary vaccination. Reactogenicity was assessed for 7 days after vaccination. This trial was registered with ClinicalTrials.gov (NCT03908164).

FINDINGS

Between May 7, 2019, and Feb 13, 2020, of 1010 women assessed for eligibility, 364 women were recruited and 351 received the intervention (120 in group 1, 119 in group 2, and 112 in group 3). Equivalence of time periods was demonstrated for anti-pertussis toxin and anti-pertactin IgG concentrations. The cord blood geometric mean concentrations of anti-filamentous haemagglutinin IgG were higher with increasing gestational age at vaccination, such that for infants in group 1 (≤23 weeks + 6 days), equivalence to group 3 (28-31 weeks + 6 days) was not shown. Reported rates of fever were similar between study groups.

INTERPRETATION

Pertussis vaccination at three different time intervals in pregnancy resulted in equivalent concentrations of IgG antibodies in infants against two of the three pertussis antigens assessed. Overall, these findings support recommendations to vaccinate any time between 16 weeks and 32 weeks of gestation.

FUNDING

The Thrasher Research Fund and the National Immunisation Schedule Evaluation Consortium through the National Institute for Health and Care Research policy research programme.

The association between maternal influenza vaccination during pregnancy and adverse birth outcomes in the United States: Pregnancy risk Assessment Monitoring System (PRAMS)

OBJECTIVE

Influenza vaccination during pregnancy is highly recommended. We examined the association between maternal influenza vaccination and adverse birth outcomes.

METHODS

This cross-sectional study used data from the Pregnancy Risk Assessment Monitoring System (PRAMS) during 2012-2017. The primary exposure was the receipt of influenza vaccination during pregnancy. Low birth weight (LBW), preterm birth (PTB), and small for gestational age (SGA) were the primary outcomes. We conducted multivariable logistic regression models to estimate the adjusted odds ratios (AOR) and 95% confidence intervals (CI). Covariates used to adjust confounding included maternal age, marital status, education, race and ethnicity, insurance status before pregnancy, and smoking status. For a subgroup in 2012-2015, we analyzed the association between influenza vaccination in each trimester and adverse birth outcomes.

RESULTS

During 2012-2017, compared with unvaccinated women, women vaccinated during pregnancy had a lower risk of LBW and PTB. During 2012-2015, maternal influenza vaccination in the 1st and 3rd trimesters was associated with a reduced risk of LBW and PTB, and vaccination in the 3rd trimester had a greater protective effect than in the 1st trimester. Influenza vaccination was not associated with SGA regardless of trimester.

CONCLUSIONS

Our findings suggest that influenza vaccination during pregnancy is a safe and effective way to protect newborns.

Maternal third dose of BNT162b2 mRNA vaccine and risk of infant COVID-19 hospitalization

Infants are at a higher risk of Coronavirus Disease 2019 (COVID-19)-related hospitalizations compared to older children. In this study, we investigated the effect of the recommended third maternal dose of BNT162b2 COVID-19 vaccine during pregnancy on rates of infant COVID-19-related hospitalizations. We conducted a nationwide cohort study of all live-born infants delivered in Israel between 24 August 2021 and 15 March 2022 to estimate the effectiveness of the third booster dose versus the second dose against infant COVID-19-related hospitalizations. Data were analyzed for the overall study period, and the Delta and Omicron periods were analyzed separately. Cox proportional hazard regression models estimated hazard ratios and 95% confidence intervals (CIs) for infant hospitalizations according to maternal vaccination status at delivery. Among 48,868 live-born infants included in the analysis, rates of COVID-19 hospitalization were 0.4%, 0.6% and 0.7% in the third-dose, second-dose and unvaccinated groups, respectively. Compared to the second dose, the third dose was associated with reduced infant hospitalization with estimated effectiveness of 53% (95% CI: 36-65%). Greater protection was associated with a shorter interval between vaccination and delivery. A third maternal dose during pregnancy reduced the risk of infant hospitalization for COVID-19 during the first 4 months of life, supporting clinical and public health guidance for maternal booster vaccination to prevent infant COVID-19 hospitalization.

Protecting the Offspring, the Gift of Maternal Immunization: Current Status and Future Perspectives

Pregnancy is characterized by immunological alterations in pregnant women that permit the growth of a semi-allogenic fetus, resulting in greater susceptibility of childbearing women to infections. Furthermore, due to the immaturity of the immune system of neonates, a protection gap is present in early life, leaving neonates and infants vulnerable to infectious diseases with increased morbidity and mortality. Maternal immunization against influenza, pertussis, and, in the context of the COVID-19 pandemic, SARS-CoV-2 has been implemented in several countries, with beneficial effects on both the mother and the offspring. The main protective mechanism of vaccination during pregnancy is transplacental transfer of maternal antibodies. However, recent evidence has implied that the fetal immune system may be influenced beyond passive immunity. This review sheds light on the current status of the routinely administered vaccinations during pregnancy, focusing on the impact of maternal immunization on the priming of the fetal immune system and suggesting future perspectives for the optimization of vaccination strategies.

Pregnancy Interventions to Improve Birth Outcomes: What Are the Effects on Maternal Outcomes? A Scoping Review

Objectives: Interventions in pregnancy are commonly evaluated for their effects on birth outcomes because maternal infection and poor nutrition are the primary contributors to adverse pregnancy outcomes, especially in low- and middle-income countries (LMICs). However, the extent to which such interventions directly impact maternal health and nutrition has not been succinctly characterized.

Methods: We conducted a scoping review of systematic reviews and meta-analyses of 27 pregnancy interventions to summarize the evidence of impact on maternal outcomes.

Results: Overall, these were reported incompletely, and we failed to find any evidence for eight interventions. Influenza vaccination, insecticide-treated bed nets, intermittent preventive treatment for malaria, anthelmintic therapy, and treatment of bacterial vaginosis, asymptomatic bacteriuria, and periodontal disease during pregnancy provided direct benefit to women, with reductions in infection risk. Nutritional interventions such as micronutrient supplementation and balanced energy and protein improved outcomes of maternal anemia and gestational weight gain, particularly in deficient populations. Calcium and low dose aspirin significantly reduced the risk of pre-eclampsia.

Conclusion: These findings highlight antenatal interventions benefitting maternal health and provide insights into pathways for impacting birth and infant outcomes.

Effects of Vaccination Against Influenza, Pertussis, and COVID-19 on Human Milk Antibodies: Current Evidence and Implications for Health Equity

Human milk contains three antibody classes that confer mucosal immunity to the breastfed infant: secretory IgA (SIgA), secretory IgM (SIgM), and IgG. Influenza and pertussis vaccines administered during pregnancy induce pathogen specific SIgA and IgG responses in human milk that have been shown to protect the breastfed infant from these respiratory illnesses. In addition, mRNA vaccines against the SARS-CoV-2 virus administered during pregnancy and lactation induce anti-SARS-CoV-2 IgG and IgA responses in human milk. This review summarizes the immunologic benefits of influenza, pertussis, and COVID-19 vaccines conferred by human milk. Additionally, future research direction in human milk immunity and public health needs to improve lactational support are discussed.

Maternal immune response and placental antibody transfer after COVID-19 vaccination across trimester and platforms

The availability of three COVID-19 vaccines in the United States provides an unprecedented opportunity to examine how vaccine platforms and timing of vaccination in pregnancy impact maternal and neonatal immunity. Here, we characterize the antibody profile after Ad26.COV2.S, mRNA-1273 or BNT162b2 vaccination in 158 pregnant individuals and evaluate transplacental antibody transfer by profiling maternal and umbilical cord blood in 175 maternal-neonatal dyads. These analyses reveal lower vaccine-induced functions and Fc receptor-binding after Ad26.COV2.S compared to mRNA vaccination and subtle advantages in titer and function with mRNA-1273 versus BN162b2. mRNA vaccines have higher titers and functions against SARS-CoV-2 variants of concern. First and third trimester vaccination results in enhanced maternal antibody-dependent NK-cell activation, cellular and neutrophil phagocytosis, and complement deposition relative to second trimester. Higher transplacental transfer ratios following first and second trimester vaccination may reflect placental compensation for waning maternal titers. These results provide novel insight into the impact of platform and trimester of vaccination on maternal humoral immune response and transplacental antibody transfer.

Maternal immune protection against infectious diseases

The maternal immune system protects developing offspring against pathogens before birth via transplacental transfer and after birth through secreted milk. This transferred maternal immunity influences each generation's susceptibility to infections and responsiveness to immunization. Thus, boosting immunity in the maternal-neonatal dyad is a potentially valuable public health strategy. Additionally, at critical times during fetal and postnatal development, environmental factors and immune stimuli influence immune development. These "windows of opportunity" offer a chance to identify both risk and protective factors that promote long-term health and limit disease. Here, we review pre- and postpartum maternal immune factors that protect against infectious agents in offspring and how they may shape the infant's immune landscape over time. Additionally, we discuss the influence of maternal immunity on the responsiveness to immunization in early life. Lastly, when maternal factors are insufficient to prevent neonatal infectious diseases, we discuss pre- and postnatal therapeutic strategies for the maternal-neonatal dyad.

Maternal vaccination: a review of current evidence and recommendations

Maternal vaccination is an effective means of protecting pregnant women, their fetuses, and infants from vaccine-preventable infections. Despite the availability of sufficient safety data to support the use of vaccines during pregnancy, maternal immunization remains an underutilized method of disease prevention, often because of concerns from both healthcare providers and pregnant women about vaccine safety. Such concerns have been reflected in the low uptake of the COVID-19 vaccine among pregnant women seen in many parts of the world. Here, we present an update of the current recommendations for the use of vaccines during pregnancy, including the evidence supporting the use of novel vaccine platforms. We also provide an overview of the data supporting the use of COVID-19 vaccines in pregnancy and an update of the status of vaccines that are currently under development for use in pregnant women.

Prenatal influenza vaccination and allergic and autoimmune diseases in childhood: A longitudinal, population-based linked cohort study

BACKGROUND

Few studies have evaluated the effect of maternal influenza vaccination on the development of allergic and autoimmune diseases in children beyond 6 months of age. We aimed to investigate the association between in utero exposure to seasonal inactivated influenza vaccine (IIV) and subsequent diagnosis of allergic and autoimmune diseases.

METHODS AND FINDINGS

This longitudinal, population-based linked cohort study included 124,760 singleton, live-born children from 106,206 mothers in Western Australia (WA) born between April 2012 and July 2016, with up to 5 years of follow-up from birth. In our study cohort, 64,169 (51.4%) were male, 6,566 (5.3%) were Aboriginal and/or Torres Strait Islander children, and the mean age at the end of follow-up was 3.0 (standard deviation, 1.3) years. The exposure was receipt of seasonal IIV during pregnancy. The outcomes were diagnosis of an allergic or autoimmune disease, including asthma and anaphylaxis, identified from hospital and/or emergency department (ED) records. Inverse probability of treatment weights (IPTWs) accounted for baseline probability of vaccination by maternal age, Aboriginal and/or Torres Strait Islander status, socioeconomic status, body mass index, parity, medical conditions, pregnancy complications, prenatal smoking, and prenatal care. The models additionally adjusted for the Aboriginal and/or Torres Strait Islander status of the child. There were 14,396 (11.5%) maternally vaccinated children; 913 (6.3%) maternally vaccinated and 7,655 (6.9%) maternally unvaccinated children had a diagnosis of allergic or autoimmune disease, respectively. Overall, maternal influenza vaccination was not associated with diagnosis of an allergic or autoimmune disease (adjusted hazard ratio [aHR], 1.02; 95% confidence interval [CI], 0.95 to 1.09). In trimester-specific analyses, we identified a negative association between third trimester influenza vaccination and the diagnosis of asthma (n = 40; aHR, 0.70; 95% CI, 0.50 to 0.97) and anaphylaxis (n = 36; aHR, 0.67; 95% CI, 0.47 to 0.95).We did not capture outcomes diagnosed in a primary care setting; therefore, our findings are only generalizable to more severe events requiring hospitalization or presentation to the ED. Due to small cell sizes (i.e., <5), estimates could not be determined for all outcomes after stratification.

CONCLUSIONS

In this study, we observed no association between in utero exposure to influenza vaccine and diagnosis of allergic or autoimmune diseases. Although we identified a negative association of asthma and anaphylaxis diagnosis when seasonal IIV was administered later in pregnancy, additional studies are needed to confirm this. Overall, our findings support the safety of seasonal inactivated influenza vaccine during pregnancy in relation to allergic and autoimmune diseases in early childhood and support the continuation of current global maternal vaccine programs and policies.

Timing of SARS-CoV-2 vaccination during the third trimester of pregnancy and transplacental antibody transfer: a prospective cohort study

OBJECTIVE

We aimed to assess the impact of early versus late third-trimester maternal severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccination on transplacental transfer and neonatal levels of SARS-CoV-2 antibodies.

METHODS

Maternal and cord blood sera were collected following term delivery after antenatal SARS-CoV-2 BNT162b2 mRNA vaccination, with the first vaccine dose administered between 27 and 36 weeks of gestation. SARS-CoV-2 spike protein (S) and receptor-binding domain (RBD) -specific, IgG levels and neutralizing potency were evaluated in maternal and cord blood samples.

RESULTS

The study cohort consisted of 171 parturients-median age 31 years (interquartile range (IQR) 27-35 years); median gestational age 39⁺⁵ weeks (IQR 38⁺⁵-40⁺⁴ weeks)-83 (48.5%) were immunized in early thrird-trimester (first dose at 27-31 weeks) and 88 (51.5%) were immunized in late third trimester (first dose at 32-36 weeks). All mother-infant paired sera were positive for anti S- and anti-RBD-specific IgG. Anti-RBD-specific IgG concentrations in neonatal sera were higher following early versus late third-trimester vaccination (median 9620 AU/mL (IQR 5131-15332 AU/mL) versus 6697 AU/mL (IQR 3157-14731 AU/mL), p 0.02), and were positively correlated with increasing time since vaccination (r = 0.26; p 0.001). Median antibody placental transfer ratios were increased following early versus late third-trimester immunization (anti-S ratio: 1.3 (IQR 1.1-1.6) versus 0.9 (IQR 0.6-1.1); anti-RBD-specific ratio: 2.3 (IQR 1.7-3.0) versus 0.7 (IQR 0.5-1.2), p < 0.001). Neutralizing antibodies placental transfer ratio was greater following early versus late third-trimester immunization (median 1.9 (IQR 1.7-2.5) versus 0.8 (IQR 0.5-1.1), p < 0.001), and was positively associated with longer duration from vaccination (r = 0.77; p < 0.001).

CONCLUSIONS

Early compared with late third-trimester maternal SARS-CoV-2 immunization enhanced transplacental antibody transfer and increased neonatal neutralizing antibody levels. Our findings highlight that vaccination of pregnant women early in the third trimester may enhance neonatal seroprotection.

The effect of gestational age at BNT162b2 mRNA vaccination on maternal and neonatal SARS-CoV-2 antibody levels

Background

COVID-19 during pregnancy and early infancy can result in severe disease. Evaluating the effect of gestational age at the time of SARS-CoV-2 vaccination on maternal antibody levels and transplacental antibody transfer has important implications for maternal care and vaccination strategies.

Methods

Maternal and cord blood sera were collected from mother/newborn dyads (n=402), following term delivery after antenatal two-dose SARS-CoV-2 BNT162b2 mRNA vaccination. SARS-CoV-2 spike protein (S) and receptor binding domain (RBD)-specific IgG levels were evaluated in the samples collected.

Results

Median anti-S and anti-RBD-specific IgG levels in maternal sera at the time of delivery were lowest following 1 ^st trimester vaccination (n=90) (anti-S IgG: 76 AU/mL, anti-RBD-specific IgG: 478 AU/mL), intermediate in those vaccinated in the 2 ^nd trimester (n=124) (anti-S IgG: 126 AU/mL, anti-RBD-specific IgG: 1263 AU/mL), and highest after 3 ^rd trimester vaccination (n=188) (anti-S IgG: 240 AU/mL, anti-RBD-specific IgG: 5855 AU/mL). Antibody levels in neonatal sera followed a similar pattern and were lowest following antenatal vaccination in the 1 ^st trimester (anti-S IgG: 126 AU/mL, anti-RBD-specific IgG: 1140 AU/mL). In a subgroup of parturients vaccinated in the 1 ^st trimester (n=30), a third booster dose was associated with significantly higher maternal and neonatal antibody levels.

Conclusions

These results suggest a considerable antibody waning throughout pregnancy in those vaccinated at early gestation. The observed boosting effect of a third vaccine dose, hints to its potential benefit in those who completed the two-dose vaccine series at early pregnancy or prior to conception. The impact of antenatal immunization timing on SARS-CoV-2 transplacental antibody transfer may influence neonatal seroprotection.

mRNA Covid-19 vaccines in pregnancy: A systematic review

OBJECTIVE

Pregnancy is a known risk factor for severe Coronavirus disease 2019. It is important to develop safe vaccines that elicit strong maternal and fetal antibody responses.

METHODS

Registries (ClinicalTrials.gov, the WHO Clinical Trial Registry, and the European Union Clinical Trial Registry) and databases (MEDLINE, ScienceDirect, Cochrane Library, Proquest, Springer, medRxiv, and bioRxiv) were systematically searched in June 20-22, 2021, for research articles pertaining to Covid-19 and pregnancy. Manual searches of bioRxiv and medRxiv were also conducted. Inclusion criteria were studies that focused on Covid-19 vaccination among pregnant women, while review articles and non-human studies were excluded. Infection rate, maternal antibody response, transplacental antibody transfer, and adverse events were described.

RESULTS

There were 13 observational studies with a total of 48,039 pregnant women who received mRNA vaccines. Of those, three studies investigated infection rate, six studies investigated maternal antibody response, seven studies investigated antibody transfer, three studies reported local adverse events, and five studies reported systemic adverse events. The available data suggested that the mRNA-based vaccines (Pfizer-BioNTech and Moderna) can prevent future SARS-CoV-2 infection. These vaccines did not show clear harm in pregnancy. The most commonly encountered adverse reactions were pain at the injection site, fatigue, and headache, but these were transient. Antibody responses were rapid after the first vaccine dose. After the booster, antibody responses were stronger and associated with better transplacental antibody transfer. Longer intervals between first vaccination dose and delivery were also associated with higher antibody fetal IgG and a better antibody transfer ratio.

CONCLUSIONS

The SARS-CoV-2 mRNA vaccines are encouraged for pregnancy. These vaccines can be a safe option for pregnant women and their fetuses. Two vaccine doses are recommended for more robust maternal and fetal antibody responses. Longer latency is associated with higher fetal antibody responses. Further research about its long-term effect on pregnancy is needed.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO (CRD42021261684).

Comprehensive Serological Profile and Specificity of Maternal and Neonatal Cord Blood SARS CoV-2 Antibodies

OBJECTIVE

To describe the profile and specificity of maternal and neonatal cord-blood antibody profile in response SARS-CoV-2 virus exposure.

METHODS

This is a Prospective cohort study of delivering patients at Thomas Jefferson University Hospital from April 2020-February 2021. Primary objective was to describe unique maternal and fetal antibody epitope titers and specificity in those patients with COVID-19 history. Serologic profile assessed with a multiplex platform. Antigens used were: HA-trimer Influenza A (Hong Kong H3), spike trimers for SARS-CoV-2, SARS-CoV-1, MERS-CoV, and betacoronaviruses HKU-1 and OC43, as well as the spike N-terminal domain (NTD), spike receptor binding domain (RBD), and nucleocapsid protein (N; full length) for SARS-CoV-2.

RESULTS

112 maternal samples and 101 maternal and cord blood pairs were analyzed. Thirty-seven had a known history of COVID-19 (positive PCR test) in the pregnancy and of those, 17 (47%) were diagnosed with COVID-19 within 30 days of delivery. Fifteen of remaining seventy-six (20%) without a known diagnosis had positive maternal serology. For those with history of COVID-19 we identified robust IgG response in maternal blood to CoV2 nucleocapsid (N), spike (S) full-length and S (RBD) antigens with more modest responses to the S (NTD) antigen. By contrast, the maternal blood IgM response appeared more specific to S (full-length), than N, S (RBD) or S (NTD) epitopes. There were significantly higher maternal and cord blood IgG response not just to CoV2 spike (p < 10 ^-18 ), but also CoV1 spike (p < 10 ^-9 ) and MERS spike (p < 10 ^-8 ). By contrast, maternal IgM responses were more specific to CoV2 (p < 10 ^-19 ), but to a lesser degree for CoV1 (p < 10 ^-5 ), and no significant differences for MERS. Maternal and cord-blood IgG were highly correlated for both S and N (R ² = 0.96 and 0.94).

CONCLUSIONS

Placental transfer is efficient, with robust N and S responses. Both nucleocapsid and spike antibody responses should be studied for a better understanding of COVID-19 immunity. IgG antibodies are cross reactive with related CoV-1 and MERS spike epitopes while IgM, which cannot cross placenta to provide neonatal passive immunity, is more SARS CoV-2 specific. Neonatal cord blood may have significantly different fine-specificity than maternal blood, despite the high efficiency of IgG transfer.

Comprehensive Serological Profile and Specificity of Maternal and Neonatal Cord Blood SARS CoV-2 Antibodies

BACKGROUND

Initial studies on COVID-19 in pregnancy have demonstrated a range of neutralizing activity, but little has been published on the full profile of SARS CoV-2 related antibodies in maternal and cordblood.

OBJECTIVE

This study aimed to describe the profile and specificity of maternal and neonatal cord blood antibody profiles in response to SARS-CoV-2 virus exposure.

STUDY DESIGN

This was a prospective cohort study of delivering patients at Thomas Jefferson University Hospital from April 2020 to February 2021. The primary objective was to describe unique maternal and fetal antibody epitope titers and specificity in patients with COVID-19 history. Serologic profile was assessed with a multiplex platform. Antigens used were hemagglutinin trimer influenza A (Hong Kong H3); spike trimers for SARS-CoV-2, SARS-CoV-1, Middle East respiratory syndrome coronavirus, and betacoronaviruses HKU-1 and OC43; and spike N-terminal domain, spike receptor-binding domain, and nucleocapsid protein (full length) for SARS-CoV-2.

RESULTS

Here, 112 maternal samples and 101 maternal and cord blood pairs were analyzed. Of note, 37 patients had a known history of COVID-19 (positive polymerase chain reaction test) during pregnancy. Of 36 patients, 16 (44%) were diagnosed with COVID-19 within 7 days of delivery. Moreover, 15 of the remaining 76 patients (20%) without a known diagnosis had positive maternal serology. For those with a history of COVID-19, we identified robust immunoglobulin G response in maternal blood to CoV-2 nucleocapsid, spike (full length), and spike (receptor-binding domain) antigens with more modest responses to the spike (N-terminal domain) antigen. In contrast, the maternal blood immunoglobulin M response seemed more specific to spike (full length) epitopes than nucleocapsid, spike (receptor-binding domain), or spike (N-terminal domain) epitopes. There were significantly higher maternal and cord blood immunoglobulin G responses not only to CoV-2 spike (127.1-fold; standard deviation, 2.0; P<.00001) but also to CoV-1 spike (21.1-fold higher; standard deviation, 1.8; P<.00001) and Middle East respiratory syndrome spike (6.9-fold higher; standard deviation, 2.5; P<.00001). In contrast, maternal immunoglobulin M responses were more specific to CoV-2 spike (15.8-fold; standard deviation, 2.1; P<.00001) but less specific to CoV-1 (2.5-fold higher; standard deviation, 0.71; P<.00001) and no significant difference for Middle East respiratory syndrome. Maternal and cord blood immunoglobulin G antibodies were highly correlated for both spike and nucleocapsid (R²=0.96 and 0.94, respectively).

CONCLUSION

Placental transfer was efficient, with robust nucleocapsid and spike responses. Both nucleocapsid and spike antibody responses should be studied for a better understanding of COVID-19 immunity. Immunoglobulin G antibodies were cross-reactive with related CoV-1 and Middle East respiratory syndrome spike epitopes, whereas immunoglobulin M antibodies, which cannot cross the placenta to provide neonatal passive immunity, were more SARS-CoV-2 specific. Neonatal cord blood may have significantly different fine specificity than maternal blood, despite the high efficiency of immunoglobulin G transfer.

Society for Maternal-Fetal Medicine Special Statement: COVID-19 research in pregnancy: progress and potential

The COVID-19 global pandemic has broad implications for obstetrical care and perinatal outcomes. As we approach the 2-year mark into an unprecedented international pandemic, this review presents the progress and opportunities for research related to COVID-19 and pregnancy. Research is the basis for evidence-based clinical guidelines, and we aim to provide the structure and guidance for framing COVID-19-related obstetrical research. This structure will pertain not only to this pandemic but future ones as well.

Role of maternal COVID-19 vaccination in providing immunological protection to the newborn

Pregnant and postpartum individuals are known to have an elevated risk of severe COVID-19 compared with their non-pregnant counterparts. Vaccination is the most important intervention to protect these populations from COVID-19-related morbidity and mortality. An added benefit of maternal COVID-19 vaccination is transfer of maternal immunity to newborns and infants, for whom a vaccine is not (yet) approved. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-specific binding and neutralizing antibodies are present in infant cord blood and breast milk following natural maternal infection and transfer of maternal immunity following COVID-19 vaccination is an area of active research. In this review, we synthesize the available research, discuss knowledge gaps, and outline factors that should be evaluated and reported when studying the transfer of maternal immunity following COVID-19 vaccination. The data reviewed herein suggest that maternal SARS-CoV-2-specific binding antibodies are efficiently transferred via the placenta and breast milk following maternal mRNA COVID-19 vaccination. Moreover, antibodies retain strong neutralizing capacity. Antibody concentrations appear to be at least as high in infant cord blood as in the maternal serum, but lower in breast milk. Breast milk IgA rises rapidly following maternal vaccination, whereas IgG rises later but may persist longer. At least two COVID-19 vaccine doses appear to be required to reach maximal antibody concentrations in cord blood and breast milk. There is no indication that infants consuming breast milk from vaccinated mothers experience serious adverse effects, although follow-up is limited. No clear pattern has emerged regarding changes in milk supply following maternal vaccination. The heterogeneity in important methodological aspects of reviewed studies underscores the need to establish standard best practices related to research on the transfer of maternal COVID-19 vaccine-induced immunity.

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.

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.

COVID-19 Vaccination in Pregnancy and Lactation: Current Research and Gaps in Understanding

The COVID-19 pandemic has demonstrated the urgent need to develop vaccine strategies optimized for pregnant people and their newborns, as both populations are at risk of developing severe disease. Although not included in COVID-19 vaccine development trials, pregnant people have had access to these vaccines since their initial release in the US and abroad. The rapid development and distribution of novel COVID-19 vaccines to people at risk, including those who are pregnant and lactating, presents an unprecedented opportunity to further our understanding of vaccine-induced immunity in these populations. In this review, we aim to summarize the literature to date on COVID-19 vaccination in pregnancy and lactation and highlight opportunities for investigation that may inform future maternal vaccine development and implementation strategies.

Reliability of information available on popular websites about vaccination of pregnant women

OBJECTIVE

To analyze the reliability of information available on popular websites about vaccination of pregnant women according to the recommendations of the Brazilian Ministry of Health.

METHOD

Descriptive and comparative study. For data collection, a checklist composed of information on recommended, contraindicated, and indicated vaccines in special situations during pregnancy, according to the Ministry of Health, was elaborated.

RESULTS

None of the analyzed websites presented all the recommended information. Contraindications, most common adverse events, simultaneous administration of vaccines, information on the DT vaccine, and recommended vaccines in special situations were presented by a minority of websites.

CONCLUSION

Information available on websites about the vaccination of pregnant women is not always based on the recommendations and misinformation may interfere with the acceptance of this practice. The importance of the professionals of the multidisciplinary team as information mediators, particularly the nurse, is emphasized, as is the need for regulating the production and dissemination of information on the internet.

Body mass index and vaccine responses following influenza vaccination during pregnancy

BACKGROUND AND AIMS

Influenza vaccination is recommended by the World Health Organisation for pregnant women, offering the dual benefit of protecting pregnant women and their newborn infants against influenza infection. Various factors can influence vaccine immunogenicity, with obesity being one factor implicated in varied responses. This study aimed to investigate the impact of body mass index (BMI) on vaccine responses following influenza vaccination during pregnancy.

METHODS

Pregnant women attending the Women's and Children's Hospital in South Australia during 2014-2016 were invited to participate. Participant's clinical and demographic factors were recorded prior to administration of licensed seasonal influenza vaccination. Blood samples were collected before and one month post-vaccination to measure antibody responses by haemagglutination inhibition (HI) assay. Seroprotection was defined as a post-vaccination HI titre ≥ 1:40. Regression models assessed associations with failure to achieve seroprotective antibodies to H1, H3, and B influenza strains.

RESULTS

A total of 96 women were enrolled in the study at a median gestation of 22 weeks with a BMI range of 18-49 kg/m². Paired sera samples were available for 90/96 (94%). Most pregnant women (72/90, 80%) demonstrated seroprotective antibody titres to all three influenza vaccine antigens (A(H1N1)pdm09, A(H3N2), B/Yamagata) following vaccination. Compared with women with BMI < 30 kg/m², those with high BMI were less likely to fail to achieve seroprotective antibodies, however this was not statistically significant (RR 0.42, 95% CI 0.11-1.68; p = 0.22). A greater proportion of women vaccinated during their second (47/53, 93%) or third trimester (18/25, 72%) demonstrated seroprotection to all three vaccine antigens following vaccination compared with women vaccinated during their first trimester (7/12, 58%).

CONCLUSION

High BMI did not impair seroprotection levels following influenza vaccination in pregnant women. Gestation at vaccination may be an important consideration for optimising vaccine protection for pregnant women and their newborns. Further assessment of first trimester influenza vaccine responses is warranted.

Coverage and Timing of Influenza Vaccination Among Privately Insured Pregnant Women in the United States, 2010-2018

OBJECTIVE

Pregnant women are at increased risk of serious complications from influenza and are recommended to receive an influenza vaccination during pregnancy. The objective of this study was to assess trends, timing patterns, and associated factors of influenza vaccination among pregnant women.

METHODS

We used 2010-2018 MarketScan data on 1 286 749 pregnant women aged 15-49 who were privately insured to examine trends and timing patterns of influenza vaccination coverage. We examined descriptive statistics and identified factors associated with vaccination uptake by using multivariate log-binomial and Cox proportional hazard models.

RESULTS

In-plan influenza vaccination coverage before delivery increased from 22.0% during the 2010-2011 influenza season to 33.2% during the 2017-2018 influenza season. About two-thirds of vaccinated women received the vaccine in September or October during each influenza season. For women who delivered in September through May, influenza vaccination coverage increased rapidly at the beginning of influenza season and flattened after October. For women who delivered in June through August, influenza vaccination coverage increased gradually until February and flattened thereafter. Most vaccinated women who delivered before January received the vaccine in the third trimester. Increased likelihood of being vaccinated was associated with age 31-40, living in a metropolitan statistical area, living outside the South, enrollment in a consumer-driven or high-deductible health plan, being spouses or dependents of policy holders, and delivery in November through January.

CONCLUSIONS

Despite increases during the past several years, vaccination uptake is still suboptimal, particularly after October. Health care provider education on timing of vaccination and recommendations throughout influenza seasons are needed to improve influenza vaccination coverage among pregnant women.

Immunization in the Neonatal Intensive Care Unit

Premature infants admitted to the neonatal intensive care unit are at risk for severe infections and infectious complications caused by vaccine-preventable diseases. Both maternal and neonatal vaccination prevent such infections and improve outcomes for premature infants. An understanding of vaccine efficacy, safety, and administration recommendations, as well as reasons for vaccine hesitancy among clinicians and caregivers, facilitate strategies for improving vaccination rates for infants in the neonatal intensive care unit. Timely vaccination of premature infants confers important protection and improves vaccination rates during childhood.

Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) Antibodies in Neonatal Cord Blood After Vaccination in Pregnancy

BACKGROUND

Studies evaluating the safety and efficacy of currently available vaccines for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) do not include pregnant participants. No data are available to counsel on vaccine safety and potential for neonatal passive immunity.

CASE

A 34-year-old multigravid patient working in health care received the Pfizer-BioNTech (BNT162b2) mRNA vaccine for SARS-CoV-2 in the third trimester of pregnancy. Uncomplicated spontaneous vaginal delivery of a female neonate with Apgar scores of 9 and 9 occurred at term. The patient's blood as well as neonatal cord blood were evaluated for SARS-CoV-2-specific antibodies. Both the patient and the neonate were positive for antibodies at a titer of 1:25,600.

CONCLUSION

In this case, passage of transplacental antibodies for SARS-CoV-2 was shown after vaccination in the third trimester of pregnancy.

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.

Influenza in High-Risk Hosts-Lessons Learned from Animal Models

Factoring significantly into the global burden of influenza disease are high-risk populations that suffer the bulk of infections. Classically, the very young, very old, and pregnant women have been identified as high-risk populations; however, recent research has uncovered several other conditions that contribute to severe infection. By using varied animal models, researchers have identified molecular mechanisms underpinning the increased likelihood for infection due to obesity and malnourishment, as well as insight into the role sex hormones play in antiviral immunity in males, in females, and across the life span. Additionally, novel comorbidity models have helped elucidate the role of chronic infectious and genetic diseases in influenza virus pathogenesis. Animal models play a vital role in understanding the contribution of host factors to influenza severity and immunity. An in-depth understanding of these host factors represents an important step in reducing the burden of influenza among the growing number of people living with one or more chronic medical conditions.

The epidemiology of seasonal influenza after the 2009 influenza pandemic in Africa: a systematic review

Background

Influenza infection is a serious public health problem that causes an estimated 3 to 5 million cases and 250,000 deaths worldwide every year. The epidemiology of influenza is well-documented in high- and middle-income countries, however minimal effort had been made to understand the epidemiology, burden and seasonality of influenza in Africa. This study aims to assess the state of knowledge of seasonal influenza epidemiology in Africa and identify potential data gaps for policy formulation following the 2009 pandemic.

Method

We reviewed articles from Africa published into four databases namely: MEDLINE (PubMed), Google Scholar, Cochrane Library and Scientific Research Publishing from 2010 to 2019.

Results

We screened titles and abstracts of 2070 studies of which 311 were selected for full content evaluation and 199 studies were considered. Selected articles varied substantially on the basis of the topics they addressed covering the field of influenza surveillance (n=80); influenza risk factors and co-morbidities (n=15); influenza burden (n=37); influenza vaccination (n=40); influenza and other respiratory pathogens (n=22) and influenza diagnosis (n=5).

Conclusion

Significant progress has been made since the last pandemic in understanding the influenza epidemiology in Africa. However, efforts still remain for most countries to have sufficient data to allow countries to prioritize strategies for influenza prevention and control.

Comparison of influenza antibody titers among women who were vaccinated in the 2nd and the 3rd trimesters of pregnancy

BACKGROUND

We compared cord blood antibody titers in unvaccinated pregnant women to those vaccinated with seasonal influenza vaccine during the 2^nd and the 3^rd trimesters.

METHODS

Pregnant women had cord blood collected at delivery for hemagglutination inhibition assay against vaccine reference viruses: A/California/07/2009 (H1N1)pdm09, A/Switzerland/9715293/2013 (H3N2), and B/Phuket/3073/2013 (Yamagata lineage). Geometric mean titer (GMT) ratios were calculated comparing vaccinated versus unvaccinated pregnant women, and women vaccinated in the 2^nd and the 3^rd trimesters. Proportions of women achieving defined titers were compared using the χ² test.

RESULTS

Of 307 women, 190 (62%) were unvaccinated. Fifty and 67 were vaccinated during the 2^nd and the 3^rd trimesters, respectively. Median enrollment age was 29 years (interquartile range 24-34). Sixteen (5%) women had pre-existing conditions, but none were immunocompromised. GMT ratios comparing vaccinated and unvaccinated women were 5.90 (95% confidence interval [CI] 5.06-6.96) for influenza A/California, 5.39 (95% CI 4.18-6.08) for influenza A/Switzerland, and 5.05 (95% CI 4.43-5.85) for influenza B/Phuket. Similarly, the GMT ratios comparing the 3^rd and the 2^nd trimester vaccinated women were 2.90 (95% CI 2.54-3.39), 2.82 (95% CI 2.56-3.13), and 2.83 (95% CI 2.56-3.14), respectively. The proportions of women with defined titers for the three vaccine reference viruses did not differ between 2^nd and 3^rd trimester vaccinated women (titers ≥40: 68-92% versus 70-93%; ≥110: 32% versus 33-63%; and ≥330: 4-10% versus 3-21%).

CONCLUSIONS

Pregnant women vaccinated against influenza had more placental transfer of influenza antibodies to their infants than unvaccinated women. Placental transfer of antibodies was higher among those vaccinated in the 3^rd trimester than in the 2^nd trimester. There was no difference in the proportions of women achieving antibody titers corresponding to protection against influenza in children. Findings support the current World Health Organization's recommendation that pregnant women may be vaccinated in either 2^nd or 3^rd trimester of pregnancy.

Current Resources for Evidence-Based Practice, July 2020

An extensive review of new resources to support the provision of evidence-based care for women and infants. The current column includes a discussion of whether it is ethical not to offer doula care to all women, and commentaries on reviews focused on folic acid and autism spectrum disorder, and timing of influenza vaccination during pregnancy.

Influenza Vaccination Experiences of Pregnant Women as a Predictor of the Intention to Become Vaccinated in Future Pregnancies in Spain

A good perception of the vaccines administered during pregnancy favors immunization coverage, which is still not optimal for the influenza vaccine. To understand the predisposition towards vaccination in future pregnancies, a study was performed that evaluated the experiences of women with the vaccine or influenza. A cross-sectional study was conducted through telephone interviews given to a total of 683 postpartum women in two health departments from the Valencia Community (Spain). This interview asked about their intention of becoming vaccinated in future pregnancies and whether they were favor or against vaccination. Most of them, 98.5% (n = 673 [95% CI: 97.6–99.4]) (p < 0.001) declared having received the systematic vaccines throughout their lives. The ones who were vaccinated against influenza, 91.9% (n = 387 [95% CI: 89.2–94.6]) (p < 0.001) manifested they would do so in future pregnancies. The probability of future non-vaccination was modeled, which was related to an unfavorable opinion towards vaccines (OR = 4.07 [95% CI: 2.01–8.24]) (p < 0.001), having suffered from influenza during pregnancy (OR = 3.84 [95% CI: 1.41–10.42]) (p < 0.05), and not having been vaccinated during previous pregnancies (OR = 38.47 [95% CI: 23.58–62.76]) (p < 0.001). Vaccination during pregnancy increases the intent of vaccination in the future.

Vaccination during pregnancy: current and possible future recommendations

Immunizing pregnant women to protect the mother, fetus and infant from infection has increasingly been used over the last decade. Protection against infectious diseases in neonates is mainly provided by maternal antibodies transferred from mother to infant during pregnancy through transplacental transport or after delivery via breastfeeding. Both the transplacental- and breast milk-derived maternal antibodies function as the primary source of protection against infectious diseases in neonates during the first vulnerable weeks of life. During recent infectious disease outbreaks (influenza, pertussis, Zika…) and for other infectious diseases (CMV, GBS…), pregnant women are increasingly identified as an important target for vaccination. For some of these diseases, vaccines are already on the market, and recommended during pregnancy. For others, vaccines are currently under development; furthermore, some are even specifically designed to be administered during pregnancy.Conclusion: This review article provides an overview on the rationale and main mechanism of the maternal vaccination strategy and gives a summary about the current and possible future recommendations for maternal vaccination.What is Known:• Maternal vaccination has a far-reaching potential in the protection of both women and offspring.• Currently, tetanus, pertussis and influenza vaccination during pregnancy is recommended in some countries. Several new vaccines specifically designed for use in pregnancy are currently under development.What is New:• Review providing a timely overview of the rationale and main mechanisms of the maternal vaccination strategy• Up-to-date summary of the current and possible future recommendations for maternal vaccination.

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.

Maternal tetanus, diphtheria, and acellular pertussis (Tdap) and influenza immunization: an overview

BACKGROUND

Maternal tetanus, diphtheria, and acellular pertussis (Tdap) and influenza immunization for women during pregnancy (the so-called "maternal immunization") has been introduced in several countries, and recently also in Italy, to protect mother and fetus during pregnancy, infant in his first months of life and mother during postpartum period. However, very low vaccination coverage rates have been reached due to several variables.

METHODS

A literature search was conducted on PubMed and Embase, including any experimental or observational studies, to assesses existing evidence on the effectiveness, efficacy, safety and optimal timing of administration of Tdap and influenza immunization in pregnancy for mothers and their infants. The search was finalized in August 2019.

RESULTS

Reviewing the literature, we identified only a few studies that, among several maternal and infant outcomes, found sporadic significant associations with maternal influenza immunization and even less with Tdap immunization. Moreover, most of the authors of these studies explained these findings as a result of residual confounding effect. The effectiveness of maternal influenza immunization is more complicated to prove than the effectiveness of Tdap immunization because of several reasons. Not all nations recommend and offer vaccines in the same weeks of pregnancy and this one manifests the complexity in defining the best timing for Tdap or influenza immunization.

CONCLUSIONS

The safety of maternal Tdap or influenza immunization is supported by the evidence so far, however, regular surveillance should be maintained, especially with regard to the influenza vaccine that changes in formulation each year. There is a need to optimize the timing of vaccination in pregnancy and to have a national system of detection of maternal immunization in each country.

Optimal timing of influenza vaccine during pregnancy: A systematic review and meta-analysis

BACKGROUND

Pregnant women have an elevated risk of illness and hospitalisation from influenza. Pregnant women are recommended to be prioritised for influenza vaccination during any stage of pregnancy. The risk of seasonal influenza varies substantially throughout the year in temperate climates; however, there is limited knowledge of how vaccination timing during pregnancy impacts the benefits received by the mother and foetus.

OBJECTIVES

To compare antenatal vaccination timing with regard to influenza vaccine immunogenicity during pregnancy and transplacental transfer to their newborns.

METHODS

Studies were eligible for inclusion if immunogenicity to influenza vaccine was evaluated in women stratified by trimester of pregnancy. Haemagglutination inhibition (HI) titres, stratified by trimester of vaccination, had to be measured at either pre-vaccination and within one month post-vaccination, post-vaccination and at delivery in the mother, or in cord/newborn blood. Authors searched PubMed, Scopus, Web of Science and EMBASE databases from inception until June 2016 and authors of identified studies were contacted for additional data. Extracted data were tabulated and summarised via random-effect meta-analyses and qualitative methods.

RESULTS

Sixteen studies met the inclusion criteria. Meta-analyses found that compared with women vaccinated in an earlier trimester, those vaccinated in a later trimester had a greater fold increase in HI titres (1.33- to 1.96-fold) and higher HI titres in cord/newborn blood (1.21- to 1.64-fold).

CONCLUSIONS

This review provides comparative analysis of the effect of vaccination timing on maternal immunogenicity and protection of the infant that is informative and relevant to current vaccine scheduling for pregnant women.