Safety and protective effects of maternal influenza vaccination on pregnancy and birth outcomes: A prospective cohort study

Influenza vaccination hesitancy and related factors among pregnant and breastfeeding women: A cross-sectional study

Achieving safe influenza vaccination coverage among pregnant and breastfeeding women is a global health goal due to the potential risks of serious influenza for both mother and child. However, vaccine hesitancy remains a significant barrier to vaccination uptake. Since anxiety represents a determinant in vaccine decision-making, this study aimed to assess influenza vaccination hesitancy and anxiety levels in this population and to explore the association between women's characteristics, their reluctance, and anxiety levels. A multicentre, cross-sectional study was conducted between February and June 2022 using structured phone interviews to assess: (1) socio-demographics and clinical history; (2) anti-flu vaccination status, previous anti-flu vaccination, and Sars-CoV-2 infection history; (3) insights into influenza vaccination during pregnancy; (4) attitudes toward anti-flu vaccination, using the Vaccination Attitudes Examination (VAX) Scale; (5) anxiety levels, measured by the Self-Rating Anxiety Scale (SAS). Among the 387 participants, 22.8% were already vaccinated or expressed willingness to be vaccinated against influenza, and 54% had an anxiety disorder. While anxiety was not significantly associated with vaccine hesitancy, ongoing pregnancy emerged as an independent predictor of anxiety. Higher educational levels, ongoing pregnancy, already being vaccinated or willingness to get vaccinated, and being employed were associated with reduced vaccine hesitancy, while prior SARS-CoV-2 infection with increased hesitancy. Fear of unpredictable events and lack of healthcare professionals' recommendations emerged as reasons for vaccine reluctance. Given the low coverage rates, these findings highlight the need for health services to enhance vaccination efforts and provide clear recommendations to counter misinformation and ensure accurate vaccine safety information.

Safety of pertussis vaccination in pregnancy and effectiveness in infants: a Danish national cohort study 2019-2023

OBJECTIVES

Recent surges in pertussis spread have renewed focus on pertussis vaccination strategies. Denmark implemented pertussis vaccination during pregnancy in 2019 to protect infants under 3 months. This nationwide study assessed the real-world safety and effectiveness of acellular pertussis vaccination during pregnancy.

METHODS

Using nationwide Danish registers, we included all pregnancies beyond 24 gestational weeks and all liveborn children from November 1, 2019, to June 1, 2023, with follow-up until December 31, 2023. Maternal safety outcomes included hypertension, preeclampsia, chorioamnionitis, preterm birth, and stillbirth. Infant safety outcomes included neonatal mortality, neonatal intensive care unit admission, and sepsis. Vaccine effectiveness was evaluated against laboratory-confirmed pertussis and related hospital contacts. For maternal safety, vaccinated individuals were matched 1:1 to unvaccinated individuals based on gestational days, calendar week, and region. Infant outcomes were assessed among the cohort of all liveborn children with follow-up until 3 months of age. Analyses were adjusted for a range of demographic, socioeconomic and medical characteristics.

RESULTS

Among 50 851 vaccinated and 50 851 unvaccinated individuals during pregnancy, initial analyses showed an increased risk of hypertension and preeclampsia after pertussis vaccination. However, after adjusting for influenza and COVID-19 vaccination during pregnancy, pertussis vaccination was not associated with increased risks of any maternal safety outcomes including hypertension (incidence rate ratio 0.98, 0.94-1.02), mild preeclampsia (0.97, 0.92-1.02), and severe preeclampsia or haemolysis, elevated liver enzymes, and low platelets (HELLP) syndrome (0.95, 0.86-1.05). Among 215 974 liveborn children, 108 350 were exposed to the vaccine. Vaccination was not associated with adverse infant outcomes and yielded a 72% (42-87%) effectiveness against laboratory-confirmed pertussis (9 vs. 32 events).

DISCUSSION

Pertussis vaccination in pregnancy was effective in preventing infant pertussis and was not associated with adverse pregnancy or infant outcomes. Future studies should, however, examine whether other vaccines or the administration of multiple vaccines during pregnancy pose an increased maternal risk of hypertensive disorders in pregnancy.

Influenza vaccination during early pregnancy and risk of major birth defects, US Birth Defects Study To Evaluate Pregnancy exposureS, 2014-2019

PURPOSE

Studies of influenza vaccination during pregnancy and major birth defects generally provide reassuring findings. To maintain public confidence, it is important to continue evaluating the safety of maternal vaccination using well characterized, population-based data. This study extended previous research to examine associations between maternal influenza vaccination and selected birth defects using data from the Birth Defects Study To Evaluate Pregnancy exposureS, a US, multisite case-control study.

METHODS

Mothers of case children (diagnosed with a birth defect) and control children (without a birth defect diagnosis) were identified from population-based birth defect surveillance programs and recruited to complete a telephone interview. Data from 2675 case and 1575 control mothers (participants) with deliveries during 2014-2019 were analyzed. Influenza vaccination exposure during the critical exposure period (one month before pregnancy through the first pregnancy month [B1P1] for spina bifida or through the third pregnancy month [B1P3] for other selected birth defects) was assessed controlling for several participant covariates. Logistic regression with propensity score adjustment was used to estimate adjusted odds ratios (aORs) and 95 % confidence intervals (CIs). Several secondary analyses were conducted. A probabilistic bias analysis examined the effect of exposure misclassification.

RESULTS

The aOR observed between B1P1 influenza vaccination exposure and spina bifida was 0.9 (95 % CI: 0.4-2.0). The aORs for B1P3 exposure and other selected birth defects examined ranged from 0.4 to 1.3, with 95 % CIs including the null except those for cleft lip ± cleft palate (aOR: 0.6; 95 % CI: 0.4-0.9) and gastroschisis (aOR: 0.4; 95 % CI: 0.2-0.7). Results from secondary analyses were similar to the primary analyses, and those from probabilistic bias analysis were similar to respective primary and secondary analyses.

CONCLUSION

Findings showed no statistically significant positive associations between influenza vaccination and the selected birth defects, supporting public health efforts to promote optimal vaccination coverage among pregnant women.

Association of Influenza Vaccination During Pregnancy with Health Outcomes in Mothers and Children: A Population-Based Cohort Study

Immunization rates of maternal influenza vaccination during pregnancy remain suboptimal, with concerns about potential harm to the mothers and their offspring. We conducted a population-based cohort study, using mother-child linked database in Korea: (a) maternal cohort between December 2019, and March 2022; (b) neonatal cohort between September 2020, and June 2021. Exposure was defined as influenza vaccination during pregnancy. Study outcomes included gestational outcomes, vaccine-related adverse events, and other health outcomes in mothers and childbirth and immune-related health outcomes in children. After 1-to-1 propensity score matching using diverse potential confounders, effect estimates with 95% confidence intervals were estimated using the log-binomial model for cumulative outcomes and the Cox proportional model for time-to-event outcomes. After 1-to-1 propensity score matching, we identified 174,008 and 53,344 pairs for the maternal and neonatal cohorts, respectively. In the maternal cohort, influenza vaccination during pregnancy was not associated with preeclampsia, antenatal bleeding, and various adverse outcomes, including neurological, vascular, blood, and lymphatic system disorders, except for marginally elevated risks of gestational diabetes mellitus (effect estimate 1.06, 95% confidence interval 1.05 to 1.08) and postpartum hemorrhage (1.05, 1.01 to 1.08). In the neonatal cohort, maternal influenza vaccination did not increase risks of childbirth (e.g., preterm/low birth weight, congenital malformations, mortality) and immune-related outcomes, except for a slightly increased risk of lower respiratory tract infection (1.06, 1.007 to 1.12). In this population-based cohort study, influenza vaccination during pregnancy was not associated with an increased risk of a range of adverse outcomes in mothers and their offspring.

Pregnancy loss <28 weeks gestation in maternal influenza and COVID-19 vaccination studies: a review of data sources, 2009-2024

OBJECTIVES

To address gaps in maternal vaccination and pregnancy loss research, large, complex datasets are needed. We aimed to identify and evaluate data sources and data collection methods currently used to capture pregnancy losses <28 weeks following maternal influenza and COVID-19 vaccination research.

STUDY DESIGN

Narrative Review.

METHODS

PubMed, CINAHL, Scopus, and Web of Science were used to identify studies that investigated pregnancy loss <28 gestational weeks following influenza and COVID-19 vaccinations from January 1st, 2009, to March 19th, 2024. Within the resulting studies, the data source(s) used to capture exposure and outcome data were identified and categorised. The capacity to capture and measure exposures, outcomes, and missing data within categories was investigated.

RESULTS

28 articles met the inclusion criteria, representing 1,113,878 participants. Most articles (n = 19) used multiple data sources within the one study, often obtaining exposure and outcome data from separate data sources. Categories of data sources included: registries, adverse reporting systems, medical records, and survey or interview methods.

CONCLUSION

Current data collection practices and existing data sources are adversely impacting data quality, and the ability to combine large datasets necessary for analysing early pregnancy loss risk factors. This also hinders our ability to evaluate the safety of early maternal vaccination and subsequent miscarriage. Establishing pregnancy loss registries using standardised data collection and coding practices, consistent terminology, and accurate exposure and outcome timing is critical. In the absence of registries, we propose an alternative source to capture both pregnancy loss and maternal vaccination data.

Receipt of Tdap or Influenza Vaccine During Pregnancy and Odds of Clinical Chorioamnionitis: A Nested Case-Control Study

OBJECTIVE

To evaluate the odds of clinical chorioamnionitis following tetanus, diphtheria, and acellular pertussis (Tdap) or influenza vaccine receipt in pregnancy.

METHODS

In this nested case-control study, a cohort of live deliveries at two United States military hospitals, 2013-2018, was initially screened for chorioamnionitis using diagnosis codes. A sample of deliveries was selected for chart review and validation. Study cases (clinical chorioamnionitis) were defined by the presence of fever and at least one additional clinical symptom during the delivery hospitalization; controls were defined by the absence of these criteria. Descriptive statistics compared characteristics of validated cases and controls, and multivariable logistic regression models estimated adjusted odds ratios (aORs) and 95% confidence intervals (CIs) with receipt of Tdap or influenza vaccine during pregnancy; observations were weighted by the inverse probability of being sampled for validation.

RESULTS

Among 6931 deliveries, 1868 were sampled for validation and 1650 (n = 305 cases, n = 1345 controls) were included for analysis. At delivery, mean age was 25.0 years for cases and 25.9 years for controls; 88.4% of cases and 63.0% of controls were primipara. Tdap vaccine was recorded in 82.8% of cases and 82.0% of controls (aOR 0.94, 95% CI 0.72, 1.23) and influenza vaccine was recorded in 61.8% of cases and 63.0% of controls (aOR 0.97, 95% CI 0.78, 1.19). Analyses that considered timing and combinations of vaccine receipt yielded similar estimates.

CONCLUSION

In this population, neither Tdap nor influenza vaccine receipt during pregnancy was associated with increased odds of clinical chorioamnionitis at delivery.

Maternal influenza vaccination and associated risk of fetal loss: A claims-based prospective cohort study

BACKGROUND

Although numerous studies support the safety of influenza vaccination during pregnancy, fewer studies have evaluated the risk of miscarriage or considered the effect of prior immunization.

METHODS

Using national de-identified administrative claims data from the Optum Labs Data Warehouse, we conducted a claims-based cohort study of 117,626 pregnancies between January 2009 and December 2018. We identified pandemic A(H1N1)pdm09 and seasonal influenza vaccinations using CPT codes. Fetal loss was defined as miscarriage, medical termination, or stillbirth as identified by ICD-10-CM diagnostic codes. Cox proportional hazard models treating influenza vaccination as a time-varying exposure, weighted for loss-to-follow-up and stratified by baseline probability of vaccination, were used to model the risk of fetal loss by exposure to influenza vaccine.

RESULTS

About 31.4 % of the cohort had a record of influenza vaccination; 10.0 % were vaccinated before pregnancy only, 17.8 % during pregnancy only, and 3.6 % before and during pregnancy. The risk of miscarriage was 39 % lower among those vaccinated during pregnancy compared to unvaccinated (adjusted hazard ratio, aHR 0.61; 95 % CI 0.50, 0.74) and was similar for medical termination or stillbirth (HR 0.69; 95 % CI 0.45, 1.03 and aHR 0.99; 95 % CI 0.76, 1.30, respectively). Similar results were observed for women who received the vaccine before and during pregnancy. We observed little to no association between vaccination before pregnancy and risk of miscarriage (HR 0.98; 95 % CI 0.76, 1.26), medical termination (HR 1.02; 95 % CI 0.46, 2.24), or stillbirth (HR 1.14, 95 % CI 0.77, 1.69).

DISCUSSION

Influenza vaccination was not associated with an increased risk of fetal loss. These results support the safety of influenza vaccine administration even when administered before or early during pregnancy.

The Impact of Obesity on Influenza Vaccine Immunogenicity and Antibody Transfer to the Infant During Pregnancy

BACKGROUND/OBJECTIVES

Influenza vaccination is recommended for pregnant women, offering the dual benefit of protecting pregnant women and their newborn infants against influenza. This study aimed to investigate the impact of body mass index (BMI) on influenza vaccine responses in pregnant women and their newborns.

METHODS

Participants included pregnant women attending the Women's and Children's Hospital in South Australia between 2018 and 2021. Maternal blood samples were collected prior to and at 1 and 6 months post-influenza vaccination to measure antibody responses by hemagglutination inhibition (HI) assay. Cord blood samples were also collected. The percentages of participants achieving HI titre ≥40 were compared between obese and non-obese groups.

RESULTS

A total of 73 women were enrolled and received quadrivalent influenza vaccination at a mean age of 32 years (range 21-44 y) and median gestation of 24 weeks (range 11-37 weeks). BMI at vaccination was ≥30 kg/m2 for 21/73 women (29%). Most pregnant women demonstrated antibody titres ≥ 40 to all four influenza vaccine strains at 1 month post-vaccination regardless of BMI category (BMI ≥ 30 kg/m2: 19/20; 95% vs. BMI < 30 kg/m2: 47/49; 96%). At 6 months post-vaccination, 12/17 (71%) obese women compared to 36/43 (84%) non-obese women (p = 0.25) maintained HI titres ≥ 40. Cord blood serology showed HI titres ≥ 40 for 11/17 (65%) infants born to mothers with BMI ≥ 30 compared to 30/35 (86%) infants delivered by mothers with BMI < 30 kg/m2.

CONCLUSIONS

A high BMI did not impair influenza vaccine antibody responses in pregnant women at 1 month post-vaccination. However, at 6 months post-vaccination, and in the cord blood samples, the percentages maintaining HI titre ≥ 40 were lower for obese women than for non-obese pregnant women.

Vaccination against seasonal flu in childhood and adolescence. Recommendations of the Advisory Committee on Vaccines and Immunizations of the Spanish Association of Pediatrics (CAV-AEP) for the 2024-2025 season

The flu is a constant threat that can sometimes cause severe forms of disease. The highest incidence rates by age group occur in children under 15 years of age, especially in those under 5 years, in whom the rate of hospitalization is also similar to the population aged 65 years and older. In addition, children are the main transmitters of the infection. In Spain, 5 influenza vaccines are authorized for the paediatric age group: three inactivated tetravalent vaccines harvested from fertilised eggs, one tetravalent inactivated vaccine obtained from cell cultures and one attenuated tetravalent vaccine for intranasal administration, which will become trivalent in the 2024-2025 season by excluding the B Yamagata lineage as recommended by the WHO. The CAV-AEP recommends systematic vaccination in children aged 6-59 months, children and adolescents belonging to risk groups, people who can transmit the flu to groups at risk of complicated flu, and household contacts or close family of infants under 6 months. From 2 years of age, the intranasal attenuated vaccine is preferred due to its greater acceptability and thus contribution to greater vaccination coverage. The CAV-AEP also considers that vaccination against influenza of healthy children and adolescents aged 5-18 years is advisable, as it provides individual protection and promotes protection at the family and community levels. It is especially important to vaccinate all health care professionals against influenza as well as pregnant women at any time during pregnancy.

Summary of the National Advisory Committee on Immunization (NACI) Updated Guidance on Influenza Vaccination During Pregnancy

Background

Seasonal influenza infection can lead to serious complications and adverse outcomes for pregnant individuals, the developing fetus and infants younger than six months of age. This supplemental statement provides an evidence summary on the safety and effectiveness of influenza vaccination in pregnant individuals, and the benefits and risks to the pregnant person, the developing fetus and infants younger than six months of age.

Methods

A systematic review was conducted on the effectiveness and safety of influenza vaccination in pregnancy. The National Advisory Committee on Immunization (NACI)'s evidence-based process was used to assess the quality of eligible studies, summarize and analyze the findings, and apply an ethics, equity, feasibility and acceptability lens to develop recommendations.

Results

The evidence suggests that influenza vaccination during pregnancy is effective in reducing the risk of laboratory-confirmed influenza infection and hospitalization in both pregnant individuals and their infants up to six months postpartum. The evidence also suggests that influenza vaccination during pregnancy does not increase the risk of non-obstetric serious adverse events in pregnant persons, infant death, spontaneous abortion, stillbirth, preterm birth, small for gestational age, low birth weight and congenital anomalies.

Conclusion

Based on this body of evidence, NACI reaffirms the safety and importance of influenza vaccination during pregnancy. NACI recommends that individuals at any stage of pregnancy should receive an age-appropriate inactivated, unadjuvanted or recombinant influenza vaccine each influenza season. Influenza vaccination may be given at the same time as, or at any time before or after administration of another vaccine, including the coronavirus disease 2019 (COVID-19) or pertussis vaccines.

Vaccination in pregnancy. Consensus document of the CAV-AEP and the SEGO

During pregnancy, physiological changes in the immune response make pregnant women more susceptible to serious infection, increasing the risk for the mother as well as the foetus, newborn and infant. All women should be correctly and fully vaccinated as they enter their reproductive years, especially against diseases such as tetanus, hepatitis B, measles, rubella and varicella. In addition to the recommended vaccines, in risk situations, inactivated vaccines could be administered to women who were not correctly vaccinated before, while attenuated vaccines are contraindicated. Despite the fact that vaccination during pregnancy is a very important preventive measure and the existing recommendations from public health authorities, scientific societies and health professionals, the vaccination coverage could clearly be improved, especially against influenza and SARS-CoV-2, so any health professional involved in the care of pregnant women should proactively recommend these vaccines. The Spanish Association of Pediatrics (AEP), through its Advisory Committee on Vaccines, and the Spanish Society of Gynaecology and Obstetrics (SEGO) recommend vaccination against the following diseases during pregnancy: against influenza and COVID-19, in any trimester of pregnancy and during the postpartum period (up to 6 months post birth) in women not vaccinated during pregnancy; against pertussis, with the Tdap vaccine, between weeks 27 and 36 of gestation (in the CAV-AEP recommendations, preferably between weeks 27 and 28); and against RSV, with RSVPreF, between weeks 24 and 36 of gestation, preferably between weeks 32 and 36.

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.

Development of MDCK-based quadrivalent split seasonal influenza virus vaccine with high safety and immunoprotection: A preclinical study

Vaccination remains the best prevention strategy against influenza. The MDCK-based influenza vaccine prompted the development of innovative cell culture manufacturing processes. In the present study, we report the effects of multiple administrations of a candidate, seasonal, MDCK-based, quadrivalent split influenza virus vaccine MDCK-QIV in Sprague-Dawley (SD) rats. Moreover, the effects of the vaccine were evaluated in terms of fertility and early embryonic development, embryo-fetal development, and perinatal toxicity in the SD rats and immunogenicity in Wistar rats and BALB/c mice. Regarding the safety profile, MDCK-QIV demonstrated tolerance in local stimulation with repeated dose administration and presented no significant effect on the development, growth, behavior, fertility, and reproductive performance of the adult male rats, maternal rats, and their offspring. MDCK-QIV elicited strong hemagglutination inhibition neutralizing antibody response and protection against the influenza virus in the mouse model. Thus, data supported that MDCK-QIV could be further evaluated in human clinical trial, which is currently underway.

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.

Placental Inflammasome mRNA Levels Differ by Mode of Delivery and Fetal Sex

Parturition signals the end of immune tolerance in pregnancy. Term labour is usually a sterile inflammatory process triggered by damage associated molecular patterns (DAMPs) as a consequence of functional progesterone withdrawal. Activation of DAMPs recruits leukocytes and inflammatory cytokine responses in the myometrium, decidua, cervix and fetal membranes. Emerging evidence shows components of the inflammasome are detectable in both maternal decidua and placenta. However, the activation of the placental inflammasome with respect to mode of delivery has not been profiled. Placental chorionic villus samples from women delivering at term via unassisted vaginal (UV) birth, labouring lower segment caesarean section (LLSCS, emergency caesarean section) and prelabour lower segment caesarean section (PLSCS, elective caesarean section) underwent high throughput RNA sequencing (NextSeq Illumina) and bioinformatic analyses to identify differentially expressed inflammatory (DE) genes. DE genes (IL1RL1, STAT1, STAT2, IL2RB, IL17RE, IL18BP, TNFAIP2, TNFSF10 and TNFRSF8), as well as common inflammasome genes (IL1B, IL1R1, IL1R2, IL6, IL18, IL18R1, IL18R1, IL10, and IL33), were targets for further qPCR analyses and Western blotting to quantify protein expression. There was no specific sensor molecule-activated inflammasome which dominated expression when stratified by mode of delivery, implying that multiple inflammasomes may function synergistically during parturition. Whilst placentae from women who had UV births overall expressed pro-inflammatory mediators, placentae from LLSCS births demonstrated a much greater pro-inflammatory response, with additional interplay of pro- and anti-inflammatory mediators. As expected, inflammasome activation was very low in placentae from women who had PLSCS births. Sex-specific differences were also detected. Placentae from male-bearing pregnancies displayed higher inflammasome activation in LLSCS compared with PLSCS, and placentae from female-bearing pregnancies displayed higher inflammasome activation in LLSCS compared with UV. In conclusion, placental inflammasome activation differs with respect to mode of delivery and neonatal sex. Its assessment may identify babies who have been exposed to aberrant inflammation at birth that may compromise their development and long-term health and wellbeing.

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.

Acceptance of a COVID-19 vaccine and associated factors among pregnant women in China: a multi-center cross-sectional study based on health belief model

Background: Vaccine hesitancy has been recognized as an urgent public health issue. We aimed to explore the acceptance of a COVID-19 vaccine and related factors among pregnant women, a vulnerable population for vaccine-preventable diseases.Methods: A multi-center cross-sectional study among pregnant women was conducted in five provinces of mainland China from November 13 to 27, 2020. We collected sociodemographic characteristics, attitude, knowledge, and health beliefs on COVID-19 vaccination. Locally weighted scatterplot smoothing regression analysis was used to assess the trends of vaccination acceptance. Multivariable logistic regression was performed to identify factors related to vaccination acceptance.Results: Among the 1392 pregnant women, the acceptance rate of a COVID-19 vaccine were 77.4% (95%CI 75.1-79.5%). In the multivariable regression model, the acceptance rate was associated with young age (aOR = 1.87, 95% CI: 1.20-2.93), western region (aOR = 2.73, 95% CI: 1.72-4.32), low level of education (aOR = 2.49, 95% CI: 1.13-5.51), late pregnancy (aOR = 1.49, 95% CI: 1.03-2.16), high knowledge score on COVID-19 (aOR = 1.05, 95% CI: 1.01-1.10), high level of perceived susceptibility (aOR = 2.18, 95% CI: 1.36-3.49), low level of perceived barriers (aOR = 4.76, 95% CI: 2.23-10.18), high level of perceived benefit (aOR = 2.18, 95% CI: 1.36-3.49), and high level of perceived cues to action (aOR = 15.70, 95% CI: 8.28-29.80).Conclusions: About one quarters of pregnant women have vaccine hesitancy. Our findings highlight that targeted and multipronged efforts are needed to build vaccine literacy and confidence to increase the acceptance of a COVID-19 vaccine during the COVID-19 pandemic, especially for vulnerable populations.

Influenza and pertussis vaccine uptake during pregnancy among Australian women in south-east Queensland, Australia

OBJECTIVES

Population-specific studies of vaccine uptake in pregnancy are necessary to monitor progress and ensure enablers to vaccination are locally relevant. We aimed to determine the uptake of influenza and pertussis vaccine during pregnancy in women in south-east Queensland and the reasons why women were choosing not to vaccinate.

METHODS

A secondary analysis of data collected in a prospective cohort study. Data were collected at enrolment during pregnancy and within six weeks of giving birth. The primary outcome was the proportion of women vaccinated during pregnancy.

RESULTS

Among 310 pregnant women, 45.8% and 69.7% were vaccinated against influenza and pertussis, respectively; 123 (39.7%) had received both vaccines. The common predictor of vaccine uptake for influenza, pertussis or both was having had any vaccine in the 12 months prior to pregnancy. Not considering the vaccines necessary and perceptions of the risk of infection were common reasons for not intending to vaccinate.

CONCLUSIONS

Antenatal vaccine uptake remains suboptimal in women in south-east Queensland. Barriers to vaccination during pregnancy are complex and vary depending on context and population. Implications for public health: More efforts are needed to promote antenatal uptake, particularly for influenza vaccine and having both the influenza and pertussis vaccines during pregnancy.

Safety of maternal pertussis vaccination on pregnancy and birth outcomes: A prospective cohort study

OBJECTIVE

To evaluate the safety of maternal pertussis vaccination on pregnancy and birth outcomes.

METHODS

The study population comprised 1272 healthy nulliparous pregnant women who participated in Screening Tests to identify poor Outcomes in Pregnancy (STOP) study at two obstetric hospitals in South Australia between 2015 and 2018. Participants were followed prospectively, with vaccination (confirmed by medical records), extensive amounts of pregnancy and birth outcome data collected by research midwives. Adjusted relative risks (aRRs) and hazard ratios (aHRs) were estimated accounting for time-varying vaccine exposure and the temporal nature of each outcome.

RESULTS

Of the 1272 women included in this study, 80.1% (n = 1019) received maternal pertussis vaccination. Vaccinated women had an average 0.22 weeks (95% CI 0.001, 0.44) longer gestation at delivery compared to unvaccinated women. Maternal pertussis vaccination was not associated with chorioamnionitis (aRR 0.71, 95% CI 0.27,1.82), gestational hypertension (aHR 1.24, 95% CI, 0.66, 2.30), preeclampsia (aHR 0.75, 95% CI 0.47, 1.18) nor preterm birth (aHR 0.99, 95% CI 0.47, 2.07). Neither risk of low birth weight (aHR 0.72, 95% CI 0.41, 1.27) nor small for gestational age infants (aHR 0.67,95% CI 0.29, 1.55) were increased following maternal pertussis vaccination. No associations between pertussis vaccination during pregnancy and adverse birth outcomes including admission to the neonatal care unit, low Apgar scores, and mechanical ventilation were observed. Results were not materially changed after adjustment for maternal influenza vaccination.

CONCLUSION

Our study provides reassuring evidence of the safety of maternal pertussis vaccination with no increased risk of adverse pregnancy and birth outcomes. These findings support recommendations for pertussis vaccination during pregnancy to prevent morbidity and mortality associated with early-infant pertussis disease.