Date of Defense:
September 20, 2011
Influenza presents a significant risk to pregnant women and infants. Evidence from previous influenza pandemics, seasonal epidemics, and the recent H1N1 pandemic demonstrates that pregnant women and infants are at increased risk for influenza-related complications. Since 2004, influenza vaccine has been recommended for pregnant women during any trimester of pregnancy. In light of this recommendation, a literature review was conducted to examine influenza vaccine efficacy, effectiveness, and safety in pregnant women, neonates, and young infants. Medline was searched for articles on maternal vaccination. Sixteen published studies from 1964-2011 were included.
None of the studies were randomized controlled studies using laboratory-confirmed influenza to measure vaccine efficacy. Four studies examined vaccine effectiveness based on clinical outcomes, one of which showed significant protection, reporting a vaccine effectiveness of 36%. The potential for maternal vaccination to protect infants was examined in seven studies. These studies reported highly varied effectiveness, ranging from no effect to 91.5% effective. The safety of influenza vaccination was supported by both active and passive surveillance. However, many studies were underpowered and while no adverse events were reported, fewer than 775 women immunized during the first trimester were followed for vaccine safety.
Vaccination against infectious disease has been an unparalleled public health success. However, studies to date provide little evidence that influenza vaccine is more than moderately effective in protecting pregnant women from influenza. Additional well-designed studies assessing clearly defined outcomes including laboratory-confirmed influenza are essential for reasoned development of public health policy and rational decision-making about influenza prevention in this population.