Influenza vaccine administered during pregnancy was 91.5% effective in preventing hospitalizations among infant offspring younger than 6 months, new research shows.

Marietta Vázquez, MD, and colleagues from the Yale University School of Medicine conducted a matched case-control study to determine whether vaccinating expecting mothers really is an effective strategy to protect infants too young to be vaccinated. The results were published in the Dec. 15 issue of Clinical Infectious Disease.

The researchers found that only 2.2% of mothers (n=91) whose children had laboratory-confirmed influenza during the study period (2000-2009) received the influenza vaccine during pregnancy vs. 19.9% of mothers (n=158) whose children did not get sick with virus.

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“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,” the researchers wrote.

They added that it might also motivate pregnant women, who are susceptible to severe forms of the disease, to comply with current vaccine recommendations.

Both the CDC and the American College of Obstetricians and Gynecologists encourage pregnant women to get vaccinated, but uptake rates remain poor and administration varies widely across health care providers.  

From 2000 to 2004, only 10% of control mothers (those whose children did not have influenza) were vaccinated during pregnancy. However, the researchers noted that these numbers rose to 15% in 2005 to 2007, and 35% in 2008 to 2009. 

Influenza is the leading cause of vaccine-preventable mortality in the United States, causing 36,000 deaths per year and 200,000 hospitalizations, with those younger than 6 months at highest risk, according to background information in the article.

“Hopefully, this evidence could also be used in community and public campaigns to improve overall vaccination rates in these high risk groups,” the researchers wrote.

They noted that the current study was not powered to assess vaccine effectiveness by influenza season and that future prospective studies are needed to evaluate longer-term effectiveness.