Two vaccines are currently recommended for pregnant women: influenza vaccine and the combined tetanus-diphtheria-acellular pertussis vaccine (Tdap). The influenza vaccine is recommended in large part because pregnant women are seven times more likely to develop severe influenza pneumonia than woman of similar age who aren’t pregnant. Pertussis-containing vaccine, on the other hand, is recommended primarily to protect infants in the first few months of life following passive transfer of maternal antibodies through the placenta.
Recently, one group of researchers studied the effect of influenza vaccine given during pregnancy to protect infants as well as their mothers (Mahdi SA, et al. Influenza Vaccination of Pregnant Women and Protection of Their Infants. N Engl J Med. 2014 Sep 4;371(10):918-31). Investigators studied 2,116 women who either were or were not given the trivalent inactivated influenza vaccine (IIV3) during pregnancy. They found that infants born to IIV3-vaccinated mothers had significantly higher titers of influenza-virus specific antibodies, as measured by hemagglutination-inhibition assays, than placebo-inoculated mothers. More importantly, while the attack rate for PCR-confirmed influenza in infants whose mothers were inoculated with placebo was 3.6 percent, the attack rate in infants of IIV3-immunized mothers was 1.9 percent. Therefore, the efficacy of influenza vaccination of mothers in protecting their infants from influenza was about 49 percent. Immunized pregnant women were also less likely to develop influenza, with a vaccine efficacy of about 50 percent.
These studies clearly show the importance of influenza vaccination in protecting both pregnant women and their infants.