Seasonal influenza affects up to 11% of pregnant women annually, and accounts for a considerable number of hospitalisations and deaths during gestation. Pregnant women are susceptible to more severe influenza infections owing to physiologic changes that affect cardiopulmonary function and cell-mediated immunity, with data suggesting that gestational influenza infection is associated with preterm birth and stillbirth.

Source: Risk of severe influenza infection in women with a history of pregnancy complications: A longitudinal cohort study | PLOS One, Public Library of Science (PLOS).