Growing evidence has demonstrated that COVID-19 vaccines during pregnancy are safe and effective. Infection with COVID during pregnancy is associated with increased risk of pregnancy complications, severe illness, and death. Public health authorities and professional organizations recommend COVID vaccination before, during and after pregnancy.

Pregnant people may worry about theoretical risks of effects of the vaccine, especially fever, on the developing fetus. On the other hand, lack of symptoms might lead someone to wonder whether the vaccine is working. New research from the COVID-19 Vaccination in Pregnancy and Lactation Study examined reactions and immune response to the vaccine during pregnancy, and health of mothers and infants until 1 year after birth.

The study found that COVID-19 vaccines provoked a robust immune response in pregnant people. There were no serious adverse events, consistent with the abundant data showing that COVID vaccines are safe during pregnancy.

Antibodies passed to infants persisted until at least 5 to 6 months of age in most cases. The transfer of antibodies was highest following vaccination during the 2nd trimester of pregnancy. Antibodies remained positive in milk samples up to 5 to 6 months postpartum, although there was a significant decrease in both 1-2 month and 5-6 month tests.

Few studies have looked at the associated between COVID vaccine reaction and immune response in pregnant people. People who reported symptoms, particularly generalized symptoms like fever, had higher antibodies after the 2nd dose and average antibodies. Mothers with symptoms had higher cord blood levels than those without symptoms. These findings suggest that general symptoms like fever are associated with a more robust immune response, resulting in higher antibodies for mothers and infants.

These results may be useful in counseling pregnant people that people with or without symptoms show adequate response to the vaccine and that symptoms are not associated with negative outcomes. The follow-up to 12 months of age for infants born with immunity from the mothers’ vaccine is important for counseling pregnant people about the benefits of the vaccine, especially in the absence of an approved COVID vaccine for infants under 6 months.