Breast milk of vaccinated mothers contains antibodies against COVID-19

There is significant increase in SARS-CoV-2-specific antibodies in breast milk of mothers following vaccination against COVID-19 — indicating its potential in conferring protection against the illness to breastfeeding infants, according to a study.

“Our findings show that vaccination results in a significant increase in antibodies against SARS-CoV-2 … in breast milk, suggesting that vaccinated mothers can pass on this immunity to their babies, something we are working to confirm in our ongoing research,” said study principal investigator Dr Joseph Larkin III from University of Florida's (UF) Institute of Food and Agricultural Sciences in Gainesville, Florida, US.

The prospective observational study involved 21 lactating healthcare workers (mean age 34 years) who had their milk and blood sampled at three time points: before vaccination with mRNA vaccine, after the first dose, and following the second dose. [Breastfeed Med 2021;doi:10.1089/bfm.2021.0122]

“We saw a robust antibody response in blood and breast milk after the second dose — about a hundred-fold increase compared with levels before vaccination,” said Lauren Stafford, who was a doctoral student of Larkin.

Compared with pre-vaccination period, SARS-CoV-2-specific IgA increased significantly in breast milk samples collected after the first (p<0.0007) and the second vaccine dose (p<0.0001).

Similarly for SARS-CoV-2-specific IgG, the levels also increased significantly in breast milk following the first (p<0.0006) and the second vaccination (p<0.0001) compared with pre-vaccination period.

“These levels are also higher than those observed after natural infection with the virus,” said lead author Dr Vivian Valcarce, also from University of Florida.

Similar findings were seen for blood plasma samples, as expected. SARS-CoV-2-specific IgG levels peaked in plasma around 7–10 days after the second dose of vaccine. Also, plasma IgG appeared to positively correlate with its levels in breast milk (p=0.043).

“The results of our study strongly suggest that vaccines can help protect both mom and baby, another compelling reason for pregnant or lactating women to get vaccinated,” said co-author Professor Josef Neu of UF’s College of Medicine.

As immune system in infancy is underdeveloped and infants are often too young to mount a sufficient immune response to vaccines, passive immunity conferred by breast milk plays an important role.

“Think of breast milk as a toolbox full of all the different tools that help prepare the infant for life. Vaccination adds another tool to the toolbox, one that has the potential to be especially good at preventing COVID-19 illness,” Neu explained.  

According to Valcarce, protecting babies through vaccination of mothers is nothing new.

“Typically, expectant mothers are vaccinated against whooping cough and flu because these can be serious illnesses for infants. Babies can also catch COVID-19, so routine vaccination of mothers against the virus could be something we see in the future,” Valcarce said.

“We would like to know if infants who consume breast milk containing these antibodies develop their own protection against COVID-19,” Larkin said. “In addition, we would also like to know more about the antibodies themselves, such as how long they are present in breast milk and how effective they are at neutralizing the virus.”