Influenza vaccination and fetal and neonatal outcomes

Abstract

As pregnant women are considered a high-risk group for severe influenza illness, current recommendations advise vaccination of all pregnant women with inactivated influenza vaccine. Nevertheless, rates of maternal influenza vaccination have historically been low, possibly reflecting ongoing concerns about vaccine safety. Until recently, the majority of evidence concerning safety of influenza vaccination during pregnancy was limited to post-marketing pharmacovigilance studies; however, in the past 5 years, one randomized clinical trial and a number of observational studies reflecting seasonal trivalent inactivated influenza vaccines and monovalent H1N1 influenza vaccines have been published. This review summarizes the evidence pertaining to fetal and neonatal outcomes following influenza vaccination during pregnancy for comparative analytic studies published between 2008 and August 2013. Since the majority of these studies are observational in nature, issues related to study quality are also addressed.

Keywords::

• epidemiology
• H1N1 influenza
• influenza
• influenza vaccination
• pregnancy
• pregnancy outcomes
• vaccine safety

Financial & competing interest disclosure

S McNeil has participated in clinical trials from influenza vaccine manufacturers (Sanofi, GSK, Novartis) and has previously received research funding from Sanofi and GSK. None of the other authors have any relevant affiliations or financial involvement with any organization or entity with a financial interest conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties.

No writing assistance was utilized in the production of this manuscript.

Key issues

• • Pregnancy increases vulnerability to the serious effects of influenza illness. Influenza illness in pregnancy has the potential to adversely affect both the woman as well as the developing fetus.

• • Only one randomized controlled trial of influenza vaccination during pregnancy (in the third trimester) has been published to date, with results showing significantly beneficial effects of influenza vaccination on small for gestational age and mean birthweight compared with pneumococcal vaccination during the putative influenza time period. Another randomized controlled trial of third trimester influenza vaccination is currently underway in Mali and will be an important addition to the evidence base on this topic.

• • The remaining evidence to date, which has been chiefly generated from observational studies, also consistently suggests that influenza vaccination during pregnancy is not associated with any increased risk of adverse perinatal outcomes. The results are most compelling for second and third trimester vaccination and for the following outcomes: fetal death, preterm birth, low birthweight and small for gestational age.

• • Despite study design and other methodological differences, results across the observational studies are generally in agreement with findings from the randomized controlled trial and with conclusions from post-marketing passive surveillance studies.

Notes