IIV during pregnancy reduces ALRI-related hospitalization in infants
Administering trivalent inactivated influenza vaccine (IIV) during pregnancy appears to reduce all-cause acute lower respiratory tract infection (ALRI) hospitalization among neonates during the first 3 months of life, suggesting that the vaccine has a potentially protective effect on subsequent bacterial infections that influenza may predispose infants to.
The study followed for the first 6 months of life infants born to mothers who participated in a double-blind placebo-controlled trial to assess the efficacy of IIV during pregnancy. Of the infants, 1,026 infants were born to mothers who had IIV and 1,023 were born to those who had received placebo.
During the study period, a total of 52 ALRI hospitalizations (median age 72 days) were recorded. The incidence was lower among infants born to IIV-recipients than among those born to placebo recipients (19 vs 33; 3.4 vs 6.0 per 1,000 infant-months), with a vaccine efficacy of 43.1 percent (p=0.050).
Thirty of the ALRI hospitalizations occurred during the first 90 days of life, accounting for nine in the IIV group and 21 in the placebo group (incidence rate ratio, 0.43; 95 percent CI, 0.19 to 0.93) for a vaccine efficacy of 57.5 percent (p=0.032).
Among infants aged >3 months, the incidence of ALRI hospitalizations was comparable between the IIV and placebo groups.
Finally, among the 44 hospitalized infants who were tested for influenza virus infection, only one tested positive.
With immunization considered the best strategy for flu prevention, the current recommendation by the Centers for Disease Control and Prevention states that all pregnant women be administered IIV during flu season. Previous studies have reported that the vaccine yields up to a 70-percent reduction in flu and a 36-percent reduction in influenza in mothers. [Obstet Gynecol 2015;125:212–226]
The vaccination may also confer partial protection against influenza in infants aged ≤6 months, who are at high risk of influenza-associated hospitalization and whose immune responses to IIV vaccination are poor. [N Engl J Med 2014;371:918-931]