Women vaccinated against COVID-19 in their first and third trimesters have a stronger immune response than those vaccinated in their second trimester, new research shows.

Placental transfer of SARS-CoV-2 antibodies to the fetus also appears to be more robust following first and second trimester vaccination, according to US clinicians.

“For pregnant individuals vaccinated in the first trimester, both maternal and neonatal immunity may be further enhanced by boosting in the third trimester,” the authors reported in Nature Communications.

The team, led by the Massachusetts General Hospital in Boston, profiled the vaccine-induced immune response in a cohort of 158 pregnant women (median age 34), of whom 11%, 56% and 33% were vaccinated in the first, second and third trimester, respectively.