In brief

Mothers vaccinated against COVID-19 were found to produce protective antibodies in breast milk with no concerning side effects in breastfed infants.

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Is it safe to breastfeed after the COVID-19 vaccine?

8 Mar 2022

Research reveals the safety of mRNA COVID-19 vaccines for breastfeeding mothers and the potential of passing immune protection to the baby.

The development of the mRNA COVID-19 vaccines marked the most important turning point in the pandemic. Though beset by supply and deployment issues at first, the global vaccination drive has now hit its stride, saving countless lives worldwide and allowing millions more to enjoy some degree of normalcy.

However, the vaccine ramped-up rollout has also highlighted some gaps in our understanding of this new vaccine technology. For example, experts know that seasonal flu vaccines can be safely given to breastfeeding mothers. The vaccine may also be beneficial for the baby, as protective antibodies can be passed through breast milk, readying the young immune system to fight off pathogens.

Unfortunately, there was no such certainty during the mRNA vaccine’s early days, which led to hesitancy among nursing women feeling reluctant to get their shots. While guidelines have now been updated to be more unequivocal about the safety of vaccines during pregnancy and breastfeeding, initial doubts may have lasting consequences for vaccine confidence.

To improve the understanding of mRNA vaccines during breastfeeding, a team of researchers led by Liang Wei Wang, Fellow at A*STAR’s Singapore Immunology Network (SIgN) and a recipient of the A*STAR National Science Scholarship, measured levels of IgG and IgA antibodies, key components of the immune system’s response to COVID-19, in the breast milk of women who received the Pfizer/BioNTech jab.

While other studies measured the relative ratio of IgA and IgG levels in the samples, Wang and his team looked at the absolute concentrations of each antibody type for a more direct and accurate comparison of how mRNA vaccines affect the immune system.

“We discovered that IgA and IgG were in fact produced at comparable levels, rather than IgG being the dominant antibody type as reported by others,” he said.

According to Wang, this was a significant discovery. The presence of the more stable IgA antibodies in breast milk suggests that breastfeeding after COVID-19 vaccination could also pass on some degree of immune protection to the baby.

On the other hand, traces of the vaccine itself were virtually absent in breastmilk, with only four samples testing positive for very low levels of vaccine mRNA. The team also observed no concerning side effects in the breastfed infants.

Moving forward, the researchers hope to further deepen the understanding of mRNA vaccines and breastfeeding to better inform maternity vaccination guidelines. “We are interested in how vaccine-elicited antibodies secreted into breast milk perform against SARS-CoV-2 variants of concern and how mRNA boosters given to previously infected lactating women affect protective antibody titres in milk,” Wang said.

The A*STAR-affiliated researchers contributing to this research are from the Singapore Immunology Network (SIgN).

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Low, J.M., Gu, Y., Ng, M.S.F., Amin, Z., Lee, L.Y., et al. Codominant IgG and IgA expression with minimal vaccine mRNA in milk of BNT162b2 vaccinees. npj Vaccines 6, 105 (2021). | article

About the Researcher

Liang Wei Wang is currently SIgN Fellow at the Singapore Immunology Network. He received his PhD in Virology from Harvard University and his B.A. (Hons.) from the University of Cambridge on the A*STAR National Science Scholarship. He has leveraged his expertise in human virology to advance the understanding of SARS-CoV-2 in the midst of the pandemic, co-authoring articles related to the cellular and molecular immunology of COVID-19.

This article was made for A*STAR Research by Wildtype Media Group