Risks and safety of pandemic H1N1 influenza vaccine in pregnancy: Exposure prevalence, preterm delivery, and specific birth defects

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

“…The association of seasonal influenza vaccine and prematurity has been evaluated in the USA and in Canada in 6 observational studies that used data from years prior the A/H1N1pdm2009 28,33-35,44,49 and 3 studies that were conducted following the 2009 pandemic season. 37,39,46 Data on fetal safety of A/H1N1pdm09 monovalent vaccines administered to pregnant women during the 2009/10 pandemic are available from the USA, 30,37 Canada, 43 Argentina, 29 Taiwan 38 and from several European countries. 10,27,31,32,36,40,41,45,48 Unadjuvanted vaccines were used in the North American studies, in France and a study in Taiwan.…”

“…10,27,31,32,36,40,41,45,48 Unadjuvanted vaccines were used in the North American studies, in France and a study in Taiwan. 30,37,38,40,43,48 The A/H1N1 MF56-adjuvanted formulation was evaluated in Argentina, Italy and the Netherlands. 27,29,42 Four studies in Scandinavia described the birth outcomes after vaccination with an AS03-adjuvanted influenza vaccine.…”

“…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.…”

“…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.…”

“…50 Some observational studies documented the time of vaccination in relation to the gestational age and considered vaccination as time-varying exposure. 10,37,46,48 These studies were able to account for the number of women who were exposed to the vaccine during the time they were susceptible to develop a specific outcome, which helps to minimize bias. Nonetheless due to the observational design of most studies they are still vulnerable to confounding and selection bias even after adjusted analyses.…”