Is routine influenza immunization warranted in early pregnancy?

Routine influenza immunization is recommended for select groups because of their higher risk of serious influenza outcomes. Based on that benefit-risk framework, we assessed whether routine administration of trivalent inactivated influenza vaccine (TIV) is warranted in pregnancy, beginning in 1st trimester. Higher maternal mortality due to influenza was extensively described during the 1918 and 1957 pandemics, but epidemiologic evidence thereafter is limited to case reports and a single ecologic analysis during a single season. Significantly elevated rates of hospitalization have been reported with seasonal influenza beginning in 1st trimester among women with select comorbidities and during the 2nd half of normal pregnancy. TIV protection against serious outcomes in pregnant women has not yet been shown. Although harm has also not been shown, sample size to date is insufficient to assert TIV safety in 1st trimester. Benefit-risk analysis suggests influenza immunization may be warranted at any stage of pregnancy during certain pandemics and annually among women with select comorbidities. TIV may also be warranted to protect women against influenza-related hospitalization during the 2nd half of normal pregnancy. Evidence is otherwise insufficient to recommend routine TIV as the standard of practice for all healthy women beginning in early pregnancy.