Abstract
BackgroundPregnant 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.ObjectivesTo compare antenatal vaccination timing with regard to influenza vaccine immunogenicity during pregnancy and transplacental transfer to their newborns.MethodsStudies 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.ResultsSixteen 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).ConclusionsThis 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.
Highlights
Pregnant women have a high risk of illness and hospi‐ talisation from influenza
A similar issue arises with antenatal pertussis vaccina‐ tion, where there is recent evidence that immunogenicity is higher in the second trimester compared with the third trimester, which has resulted in some countries bringing forward their recommendations for the optimal timing of pertussis immunisation in pregnancy.[64]
Given that women immu‐ nised earlier in pregnancy show evidence of immune waning by the point of delivery, our findings support current recommendations for women immunised early in their pregnancy to receive a second dose if they are still pregnant in the following influenza season
Summary
Pregnant women have a high risk of illness and hospi‐ talisation from influenza. Coverage rates in the United States and Australia have ranged from 20%‐50%.2225 Surveys have attributed these low vaccine uptake rates in part to distrust in the healthcare system, unawareness of the risks of influenza infection during pregnancy, concerns about vaccine safety for the foetus and lack of encouragement from healthcare professionals.[8,22,23,24]. A structured analysis of the optimal timing of influ‐ enza vaccination during pregnancy would inform specific scheduling recommendations to pregnant women and maximise the benefit re‐ ceived by vaccination. Previous reviews of antenatal influenza vaccination have re‐ ported limited and mixed evidence on the association between in‐ fluenza vaccination, influenza infection and adverse birth outcomes, and have not examined the relationship between vaccination tim‐ ing and immunogenicity.[21,27,28,29,30,31,32] This systematic review examined whether the timing of influenza vaccination during pregnancy af‐ fects the immunogenicity of the vaccine in the mother and transpla‐ cental transfer of antibody to the newborn
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