CDC data: Pfizer and Moderna's COVID-19 vaccines don't seem to pose serious risks during pregnancy. The preliminary findings add to evidence that the shots are safe and beneficial to mom and baby. The study had limitations, but getting COVID-19 in pregnancy remains riskier than the vaccines. The Pfizer and Moderna COVID-19 vaccines don't seem to pose any serious risk during pregnancy, according to a preliminary study using data from the US Centers for Disease Control and Prevention. The study, published Wednesday in the New England Journal of Medicine, used data from CDC's smartphone-based tracking system, called V-safe, that included 35,691 vaccinated pregnant people between December 14, 2020 and February 28, 2021.