Influenza vaccination of pregnant women protects young infants

Pregnant women who get vaccinated against influenza appear to reduce the risk for their infants younger than 6 months old from being hospitalized for influenza, according to a matched case-control study published in Clinical Infectious Diseases.

Cases included infants younger than 12 months old who were admitted for influenza to the Yale-New Haven Children’s Hospital from October 2000 to April 2009 (before the pandemic influenza A H1N1 outbreak in the area). One or 2 controls were enrolled for each case. Controls included hospitalized infants who did not test positive for influenza and matched cases by birth and hospitalization dates.

Some 157 cases and 270 controls were enrolled in the study. Findings were presented for 113 cases and 192 controls. Parents were interviewed regarding demographic characteristics, comorbidities, and possible confounders (ie, breastfeeding or susceptible persons living in the household). Researchers also analyzed the medical records of the infants’ mothers for documented influenza vaccination during pregnancy.

Two mothers (2.2%) of 91 cases and 31 mothers (19.9%) of 156 controls younger than 6 months old received vaccination against influenza while pregnant. In comparison, 1 mother (4.6%) of 22 cases and 2 mothers (5.6%) of 36 controls at least 6 months of age received influenza vaccination while pregnant.

After adjusting for potential confounders, the results indicate that influenza vaccination of pregnant women is 91.5% effective in preventing their infants less than 6 months of age from being hospitalized for influenza.

“These results have great clinical relevance, because they provide a strategy to confer protection to young infants at high risk for the disease and for whom no vaccine is currently available,” said researchers. “Furthermore, this strategy has important public health implications, because vaccination protects not only young infants but also their mothers, who are in the high-risk category for severe influenza.”

The researchers note that both the American College of Obstetricians and Gynecologists and the Centers for Disease Control and Prevention recommend that women who are pregnant during the influenza season receive the inactivated influenza vaccine and say that such influenza vaccination in these women is safe. However, despite these recommendations, influenza vaccination rates among pregnant women are low and vary widely among physicians and areas of the country.

Benowitz I, Esposito DB, Gracey KD, Shapiro ED, Vazquez M. Influenza vaccine given to pregnant women reduces hospitalization due to influenza in their infants. Clin Infect Dis. 2010;51(12):1355-1361.