Usefulness of Influenza Vaccination During Pregnancy

Abstract and Introduction

Abstract

Evaluation of: Fisher BM, Van Bockern J, Hart J et al. Pandemic influenza A H1N1 2009 infection versus vaccination: a cohort study comparing immune responses in pregnancy. PLoS ONE 7(3), e33048 (2012).
As pregnant women are at increased risk of influenza infection and influenza-related complications, immunization with inactivated influenza vaccine during the influenza season is recommended. Vaccination during pregnancy is considered to provide benefits for both the mothers and their young infants. In 2009, the novel influenza A (H1N1) virus was reported worldwide to be the cause of a widespread outbreak of acute febrile respiratory illness. The efficacy and efficiency of monovalent vaccine against 2009 H1N1 influenza virus during pregnancy has already been confirmed in several studies. This article provides further useful information regarding the persistence of maternal antibodies and the transplacental transfer of antibodies following vaccination by comparison with natural influenza infection.

Introduction

The fetus and placenta might be perceived as nonself to the maternal immune system, which is considered to be altered to tolerate the fetus during pregnancy. One alteration is attenuation of cellular immunity, which can diminish resistance to viral infections in pregnant women.^[1] In addition, physiological changes associated with pregnancy,^[2] such as increased oxygen consumption and ventilation, might explain the increased vulnerability to viral infections of the respiratory system. For these reasons, pregnant women are considered to be at high risk of influenza infection and serious influenza-related complications.

Major historical influenza pandemics such as Spanish influenza (H1N1) in 1918, Asian influenza (H2N2) in 1957 and Hong Kong influenza (H3N2) in 1968 suggested increased morbidity and mortality rates in pregnant women. In a series of cases from the 1918 pandemic influenza,^[3] approximately 50% of all pregnant women developed pneumonia, and more than half of these died, accounting for 27% of the total deaths. During the 1957 pandemic, 50% of women of reproductive age who died of influenza were pregnant.^[4]

In 2009, the novel influenza A (H1N1) virus infection was reported worldwide to be the cause of a widespread outbreak of acute febrile respiratory illness. Although the severity of this disease ranged from mild to severe, little was known about its impact on pregnant women. The CDC has summarized 34 cases of pregnant women with 2009 pandemic influenza A (H1N1) virus infection in the USA.^[5] The rate of hospitalization for infection in pregnant women was higher than that in the general population. Six of the pregnant women died, and all of these had developed pneumonia and subsequent acute respiratory distress syndrome requiring mechanical ventilation. Therefore, medical staff should consider pregnant women to be at high risk of severe illness after infection with 2009 pandemic influenza A (H1N1) virus.