Selective uptake of influenza vaccine and pregnancy outcomes

Abstract

Vaccination was associated with an increased adverse composite outcome in pregnant women without identified co-morbidity but not those with co-morbidities. This association is likely due to selection bias, which should be considered in planning of observational studies of the impact of vaccination on pregnancy outcomes.

Influenza vaccination during pregnancy: A systematic review of fetal death, spontaneous abortion, and congenital malformation safety outcomes

“…Full text articles were retrieved for 106 records, with 86 excluded after review and one study was excluded following critical appraisal. A total of 19 studies were included in this review [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27]. Fig.…”

The Effects of Influenza Vaccination during Pregnancy on Birth Outcomes: A Systematic Review and Meta-Analysis

“…[21][22][23][24][25]29 There was moderate heterogeneity among the eight studies (I 2 ¼ 54.8%, p ¼ 0.03) and the summary estimate of the meta-analysis for SGA comparing vaccinated women with nonvaccinated women was 0.96 (95% CI: 0.90, 1.03), ►Fig. 6A.…”

Review on the effects of influenza vaccination during pregnancy on preterm births

“…42 In this study a significant reduction in prematurity was seen in the vaccinated cohort in an analysis using proportional hazard models with gestational age as the time factor, whereas, when aOR was estimated using logistic regression models a similar however non-significant association between vaccination and preterm births was detected. 42 Preterm birth analyses after vaccination with seasonal IIV formulations containing pandemic strain Four studies in North America during and following the A/ H1N1 2009 pandemic assessed whether preterm birth rates differed between mothers who received seasonal influenza vaccine containing the pandemic strain and non-vaccinated women 37,39,46,47 (Table 2).…”

“…32,45 The emergence of A/H1N1pdm09 in 2009/10 led to concurrent availability of monovalent vaccine and the seasonal influenza vaccines; with four reports from North America evaluating the birth outcomes when both type of vaccines were administered during the same pregnancy. 37,43,46,47 In the observational studies, as uptake of influenza vaccination could have been biased, adjusting for potential confounders is imperative. It is anticipated that vaccinated women would be different from the non-vaccinated women in several characteristics and that the probability of receiving the vaccine would be associated with these factors.…”

“…To adjust for group differences and reduce confounding bias in observational studies 2 main approaches were used: propensity scores 31,34,37 and multiple logistic regression analysis. 10,21,27,29,30,33,35,36,39,[41][42][43][44][45][46][47][48][49] In propensity score analyses probability of vaccination is estimated as a function of available variables and then that score is used as a single matching covariate. The propensity score matching allows comparing the risks after vaccination between cohorts that had the same likelihood of being vaccinated.…”