Breastfeeding moms OK to get mRNA shots: study

A study of mothers who received the Pfizer and Moderna vaccines found no serious adverse effects in the recipients of their milk.

Dave Yasvinski 3 minute read September 9, 2021

The results should encourage lactating women to get the COVID-19 vaccine and to continue to breastfeed, researchers say. Getty

A new study has found the Pfizer and Moderna vaccines are safe for breastfeeding mothers, producing the same symptoms seen in non-nursing moms with no serious side effects observed in offspring.

The research, published in the journal Breastfeeding Medicine, sought to address enduring apprehension about a vulnerable population that was excluded from early trials into inoculation against COVID-19. “A mother’s first concern is the safety of her child,” said Christina Chambers, professor of pediatrics at UC San Diego School of Medicine and professor in the Herbert Wertheim School of Public Health and Human Longevity Science. “Our study, along with previous research, suggests the Pfizer and Moderna vaccines are not red flags for breastfeeding mothers and their infants.”

More than 85 per cent of the 180 breastfeeding women included in the study reported temporary localized symptoms (pain, redness, swelling at the injection site) and systemic side effects (chills, body aches, fever/vomiting) in higher frequency after their second dose — particularly the Moderna brand. A small number of women also reported a reduction in breastmilk following the first dose of either brand but significantly more after the second dose of Moderna.

“We want to emphasize that the reduction in milk supply was in a small subset of women and came back fully within 72 hours after vaccination,” Chambers said. “We also cannot be certain that the supply reduction was a side effect of the vaccine or another unknown factor. What we do know is that the vaccine is incredibly effective in providing protection from COVID-19, which has proven to be a devastating and serious virus with possible long-term side effects.”

No serious adverse effects were seen in the recipients of the milk, save for some irritability and difficulty sleeping. “We know the many benefits of breastfeeding,” Chambers said. “Breast milk provides an abundance of nutritional components to infants that provide many health benefits, from stronger immune systems to lower rates of obesity and other conditions and illnesses.

“Our results should encourage lactating women to get the COVID-19 vaccine and to continue to breastfeed their infants. They do not have to choose one over the other. Both are critical.”

Without the protection of a vaccine, the Center for Disease Control and Prevention said pregnant women are more likely to become severely ill from COVID-19 and require hospitalization or intensive care to overcome the virus — all factors that raise the risk of adverse outcomes for their unborn child. Previous study compared antibody levels in women who received an mRNA vaccine against those whose antibodies were a response to natural infection during pregnancy and found significantly higher levels among vaccine recipients. Antibodies produced by the vaccine were present in samples taken from umbilical cords and breastmilk.

The current study, which recruited participants from the Mommy’s Milk Human Milk Research Biorepository at UC San Diego, was limited by its reliance on the self-reporting of symptoms following inoculation — a shortcoming that will need to be addressed in subsequent research to improve the generalizability of results.

“This study would not be possible without the tremendous support of our staff and students, and the women across the nation who were willing to enroll and provide breast milk samples,” said Kerri Bertrand, first author of the study and research manager of the Mommy’s Milk Human Milk Research Biorepository. “Together, we are finding life-saving, evidence-based answers to crucial questions that arose when the pandemic first hit.”

Dave Yasvinski is a writer with