THURSDAY, Feb. 9, 2023 (HealthDay News) -- Maternal COVID-19 vaccination during pregnancy is highly effective against delta and moderately effective against omicron infection and hospital admission among infants, according to a study published online Feb. 8 in The BMJ.
Sarah C.J. Jorgensen, from the University of Toronto, and colleagues estimated the effectiveness of maternal mRNA COVID-19 vaccination during pregnancy against infection with severe acute respiratory syndrome coronavirus 2 delta and omicron variants and hospital admission in infants. Data were included for 8,809 infants aged younger than 6 months, born between May 7, 2021, and March 31, 2022, including 99 delta cases with 4,365 controls and 1,501 omicron cases with 4,847 controls.
The researchers found that infant vaccine effectiveness from two maternal doses was 95 and 97 percent against delta infection and hospital admission due to delta, respectively, and 45 and 53 percent against omicron infection and hospital admission due to omicron, respectively. Vaccine effectiveness for three doses was 73 and 80 percent against omicron infection and hospital admission due to omicron, respectively. For two doses, vaccine effectiveness against infant omicron infection was highest with the second dose in the third versus the first or second trimester (53 percent versus 47 and 37 percent, respectively). For two doses, vaccine effectiveness against infant omicron infection decreased from 57 percent between birth and 8 weeks to 40 percent after 16 weeks of age.
"Vaccination during the third trimester of pregnancy provided the greatest protection, and effectiveness was highest in infants between birth and 8 weeks of age," the authors write.