Efficacy and Effectiveness of Maternal Influenza Vaccination During Pregnancy: a Review of the Evidence

Influenza vaccine is universally recommended for pregnant women during any trimester of pregnancy. In light of this recommendation, a comprehensive literature review was conducted to examine the available evidence regarding influenza vaccine efficacy and effectiveness during pregnancy. A comprehensive Medline search identified potentially relevant articles published between January 1, 1964 and February 1, 2013. Articles were selected that specifically evaluated the efficacy and effectiveness of maternal influenza vaccine in protecting women and infants from influenza infection. These were reviewed with a particular focus on the methods used to confirm influenza infection. Ten of 476 articles met the inclusion criteria. None of the six studies evaluating maternal outcomes were randomized controlled studies using a laboratory-confirmed influenza diagnosis to measure vaccine efficacy. Two studies included reverse-transcriptase polymerase chain reaction confirmation; four relied solely on clinical outcomes. The reported vaccine effectiveness (VE) ranged from -15 to 70 %. Seven studies examined the potential for maternal vaccination to protect infants. Four of these applied some form of laboratory confirmation, with VE ranging from 41 to 91 %. Vaccination against infectious disease is an unparalleled public health success. However, studies to date demonstrate that influenza vaccine provides only moderate protection from influenza infection in pregnant women. This review found broad heterogeneity among studies, with no uniform outcome measured and little data based on laboratory-confirmed influenza, leading to wide-ranging estimates of effectiveness. Rigorously designed studies assessing clearly defined outcomes are needed to support the development of reasoned public health policy about influenza prevention in this population.