A small study has found that no Covid-19 mRNA vaccine is present in human breastmilk following vaccination. The study by University of California San Francisco researchers provides early evidence that the vaccine mRNA is not transferred to the infant via breastmilk.
The study analysed the breastmilk of seven women after they received the Pfizer and Moderna mRNA vaccines and found no trace of the vaccine. The findings, although from a small sample, offer the first direct data of vaccine safety during breastfeeding and could allay concerns among those who have declined vaccination or discontinued breastfeeding due to concern that vaccination might alter human milk. The paper appears in JAMA Pediatrics.
The World Health Organization recommends people should continue breastfeeding following vaccination for Covid-19.
The Academy of Breastfeeding Medicine has said there is little risk of vaccine 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 breastfeeding,” said corresponding author Stephanie L. Gaw, MD, PhD, assistant professor of Maternal-Fetal Medicine at UCSF.
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 one month to three years. Milk samples were collected prior to 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 milk.
The authors noted that the study was limited by the small sample size and said that further clinical data from larger populations was needed to better estimate the effect of the vaccines on lactation outcomes.
Golan Y, Prahl M, Cassidy A, et al. Evaluation of Messenger RNA From Covid-19 BTN162b2 and mRNA-1273 Vaccines in Human Milk. JAMA Pediatr. Published online July 06, 2021.