Asynchronous influenza vaccination and adverse maternal-child health outcomes in the Brazilian semiarid, 2013 to 2018: the INFLUEN-SA Study

Recent models indicate seasonal influenza transmission in Brazil begins annually in the semiarid state of Ceará (pop. 8.8M)—before vaccine campaigns begin. To assess the extent and maternal-child health consequences of this misalignment, we tracked severe acute respiratory infections (SARI), influenza, and influenza immunizations from 2013-2018. Of 3,297 SARI cases, 145 (4%) occurred in pregnancy. Vaccine coverage was >80%; however, campaigns often occurred during or after peak influenza. Birth weights nadired and prematurity increased 30-40 weeks following peak influenza, by a magnitude of 40g and 10.7% to 15.5%, respectively. We identified 61 babies of mothers with gestational SARI; they weighed 10% less at birth (P = 0·019) and were more often premature (OR: 2.944; 95% CI: 1.100 – 7.879) relative to controls (n=122). Mistiming of influenza vaccination adversely impacts pregnancy and birth outcomes in Ceará, with critical implications for influenza transmission dynamics nationally.