Pregnant and breastfeeding women respond to the first dose of the coronavirus vaccines more slowly than other women, and mount a less potent defense against the virus, according to a new study. After the second dose, however, their response looks almost normal.
The results, published this month in the journal Science Translational Medicine, suggest that pregnant and breastfeeding women remain susceptible to the virus for longer after vaccination. The study underscores the importance of giving these women the second dose in time, and monitoring them closely in the meantime for signs of infection.
During pregnancy, the immune system is modified to tolerate the fetus — effectively a foreign entity — leaving pregnant women particularly susceptible to pathogens like the coronavirus. Because of this, pregnant women are more likely to become severely ill and to die from Covid than other women of the same age.
Earlier research had suggested that pregnancy might also dampen the response to vaccines. But the initial trials of Covid vaccines did not include pregnant and breastfeeding women because of safety concerns, so there has been limited information about how well they respond to the inoculations.
The researchers analyzed the antibodies produced by 84 pregnant women, 31 breastfeeding women and 16 nonpregnant women of the same ages, immunized with the coronavirus vaccines made by Pfizer-BioNTech or Moderna.
After the first dose, pregnant and breastfeeding women had fewer antibodies than other women of the same age. And the antibodies were less effective at recruiting other parts of the immune system to fight the virus.
Two to six weeks after the second dose, pregnant and breastfeeding women had about as many antibodies as other women their age, consistent with results from other studies, and the qualitative differences also narrowed.
Breastfeeding women boosted their response more effectively than pregnant women after the second dose, and the quality of their immune response more closely resembled that of nonpregnant women.
The women in the study were immunized at different times during pregnancy. Future studies should analyze the optimal time during pregnancy to deliver the vaccines, the researchers said.