No Traces of COVID-19 Vaccine Found in Breastmilk

Messenger RNA vaccines against COVID-19 weren’t detected in human breastmilk, according to a small study by the University of California San Francisco (UCSF), providing early evidence that the vaccine mRNA isn’t transferred to the infant.

The study, which analyzed the breastmilk of seven women after they received the mRNA vaccines and found no trace of the vaccine, offers the first direct data of vaccine safety during breast-feeding and could allay concerns among those who have declined vaccination or discontinued breast-feeding due to concern that vaccination might alter human breastmilk. The paper appears in JAMA Pediatrics.

Research has demonstrated that vaccines with mRNA inhibit transmission of the virus that causes COVID-19. The study analyzed the Pfizer and Moderna vaccines, both of which contain mRNA.

The World Health Organization recommends that breast-feeding people be vaccinated, and the Academy of Breastfeeding Medicine has said there’s little risk of vaccine nanoparticles or mRNA entering breast tissue or being transferred to milk, which theoretically could affect infant immunity.

“The results strengthen current recommendations that the mRNA vaccines are safe in lactation, and that lactating individuals who receive the COVID vaccine should not stop breast-feeding,” says corresponding author Stephanie L. Gaw, MD, PhD, an assistant professor of Maternal-Fetal Medicine at UCSF.

“We didn’t detect the vaccine associated mRNA in any of the milk samples tested,” says lead author Yarden Golan, PhD, a postdoctoral fellow at UCSF. “These findings provide experimental evidence regarding the safety of the use of mRNA-based vaccines during lactation.”

The study was conducted from December 2020 to February 2021. The mothers’ mean age was 37.8 years and their children ranged in age from 1 month to 3 years. Breastmilk samples were collected before vaccination and at various times up to 48 hours after vaccination.

Researchers found that none of the samples showed detectable levels of vaccine mRNA in any component of the breastmilk.

The authors noted that the study was limited by the small sample size and said that further clinical data from larger populations were needed to better estimate the effect of the vaccines on lactation outcomes.

— Source: University of California San Franciso