Impact of maternal characteristics on the effect of maternal influenza vaccination on fetal outcomes

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

“…[7][8][9]11,12 All the five studies reported aOR < 1, although in only one study did the 95% CI not cross the unit. The inclusion of the Table 1 Characteristics and reported adjusted odds ratio of the studies that assessed the effect of seasonal influenza vaccine given during pregnancy and birth outcomes included in the primary meta-analyses Abbreviations: aHR, adjusted hazard ratio; aOR, adjusted odds ratio; aRR, adjusted risk ratio; BW: birth weight; GA, gestational age; LBW, low birth weight; N/A, not assessed; PTB, preterm birth; SGA, small for gestational age.…”

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

“…The highest estimates of protection of maternal vaccination against preterm deliveries were calculated during the widespread influenza activity period in the USA. 30,33,49 Nonetheless, the 40% to 70% reduction in risk of preterm deliveries during the period of viral circulation in these observational studies appears very large, taking in consideration that the efficacy of maternal vaccination is probably only 50% and that influenza infection is not associated with preterm birth rates to that level of magnitude. The A/H1N1pdm09 studies were conducted late in the pandemic season hence exposure to the virus was probably marginal, consequently, any positive effect of maternal vaccination on birth outcomes would be nonspecific and probably not attributable to the prevention of infection.…”

“…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.…”

“…Six studies evaluated the impact of seasonal IIV not containing the A/H1N1pdm09 strain on preterm birth rates when administered to pregnant women. All studies but one 28 described adjusted odds ratios (aORs) 33,34,44,49 or matched analyses. 35 All the estimated OR were lower than one, however, all the 95% confidence intervals crossed the unit.…”

“…34 Two studies using data from the Georgia Pregnancy Risk Assessment Monitoring System further stratified their analysis by births occurring during or outside influenza circulation periods. 33,49 These studies by Omer and colleagues, restricting the analyses to infants born during influenza seasons, showed a protective effect on prematurity in mothers who had received influenza vaccination during pregnancy. Consistent 70% and 60% reductions were detected in the 2004 through 2006 influenza seasons 33 and 2005 through 2008 seasons 49 using different models to control for confounding.…”