How pregnancy affects COVID-19 vaccine effectiveness

In good news for pregnant and lactating people, a recent study has shown that messenger RNA–based COVID-19 vaccines induce a robust antibody response in those who get both of the recommended shots (Sci. Transl. Med. 2021, DOI: 10.1126/scitranslmed.abi8631). During pregnancy and lactation, the immune system modifies itself because if it reacts too strongly, the body will reject the growing fetus. But the system also needs to protect against infection and pass immunity to the baby. To understand how these changes in the immune system might alter the effectiveness of COVID-19 vaccines, Andrea Edlow at Harvard Medical School and colleagues monitored the levels of protective antibodies generated after immunization. The scientists found that though pregnant and lactating people made fewer protective antibodies after the first vaccine dose than a control group, the difference disappeared after the second dose. Because antibodies are also transferred via the placenta and human milk, timing vaccination doses during pregnancy could also help protect the baby. In a second study, the researchers also found differences depending on the sex of the fetus (Sci. Transl. Med. 2021, DOI: 10.1126/scitranslmed.abi7428). People carrying male fetuses had fewer antibodies after SARS-CoV-2 infection and passed fewer antibodies across the placenta than those carrying female fetuses.