Published May 17, 2017
The Lancet Infectious Diseases

Two years have been particularly instructive when it comes to the importance of pregnant women getting immunized against the flu: 1918 and 2009.

In 1918, the global influenza pandemic killed tens of millions of people worldwide. In 2009, the influenza A H1N1 pandemic led to approximately 60.8 million cases in the U.S. alone, including 274,304 hospitalizations and 12,469 deaths.

Both instances demonstrate the danger of influenza, which presents especially high risk to pregnant women, and the importance of immunization. Both years were cited in a study led by researchers at Cincinnati Children’s that demonstrates the value of year-round maternal influenza immunization—especially in subtropical nations such as Nepal, where vaccine rates are low even though the virus circulates year round.

The study shows that higher immunization rates for mothers translates into fewer cases of low birthweight and flu in infants. The team also found that immunization did not have a discernible, negative impact on rates of miscarriage, stillbirth and congenital defects. The two-cohort study involved 3,693 women and 3,646 infants.

The study’s 11 authors included first author Mark Steinhoff, MD, director of Global Child Health, Cincinnati Children’s colleagues in Global Health and Infectious Diseases, plus researchers in Seattle, Baltimore, Washington, D.C., and Nepal.

“Our findings suggest that vaccination throughout the year might have an advantage over limited seasonal use of influenza vaccine, with its reduced probability of influenza strain-vaccine match,” the authors wrote. “Circulating viruses varied substantially, leading to limited periods of antigenic match between the trivalent inactivated vaccine used and the variety of circulating influenza viruses.”