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Vaccinated mothers transmit COVID-19 antibodies to breastfed infants

Vaccination against COVID-19 is approved for children 5 years and older, but young children and babies are also susceptible to infection. A recent study, published in the Obstetrics and Gynecology journal, found that breastfed babies can receive COVID-19 antibodies from their vaccinated mothers, giving babies passive immunity to the virus.

The cohort study included 30 breastfeeding women who were fully vaccinated with 2 doses of a COVID-19 mRNA vaccine between January and April 2021. Women were recruited across the continental United States and a minimum of 10 or more women received each vaccine (Pfizer-BioNTech or Moderna).

Participants completed questionnaires assessing their demographics, lactation status, general health status, history of COVID-19 infection, type of vaccine received, time of inoculation, and any adverse maternal or infant.

The women provided serial milk samples before vaccination, 2-3 weeks after their first dose, and 3 weeks after their second. The investigators took dried blood spots from the mothers 19 days after the first vaccine and 21 days after the second. Stool samples from infants were collected 21 days after the mothers received their second dose of vaccine.

As a control, investigators analyzed milk, blood and stool samples from infants collected before the COVID-19 pandemic. All samples were tested by enzyme immunoassay for receptor binding domain (RBD) immunoglobulin (Ig)A and IgG. Additionally, milk samples were tested for neutralizing antibodies against the spike protein of 4 COVID-19 variants of concern: D614G, Alpha (B.1.1.7), Beta (B.1.351), and Gamma (P. 1).

The results showed that the milk of vaccinated women neutralized the peak and 4 variants of concern, mainly due to the presence of anti-RBD IgG. Milk also showed a significant elevation of interferon-γ.

The immune response to maternal vaccination was confirmed by infant stool specimens. Anti-RBD IgG was detected in 33% of samples and anti-RBD IgA was detected in 30%. Notably, the levels of anti-RBD antibodies in the infants’ stools correlated with the side effects of their mothers.

Kathleen Arcaro, lead author and professor of environmental toxicology in the Department of Veterinary and Animal Sciences at the University of Massachusetts Amherst, said: “Women who felt sick from the vaccine were associated with a greater amount of antibodies in infant stool. So you may have felt bad, but it was a plus for your baby.

The researchers concluded that humoral and cellular immune responses to inoculation with a COVID-19 mRNA vaccine were present in the breast milk of most women (87%). Arcaro commented: “It’s really important because women want to know if their babies have these antibodies, and our study shows that the antibodies are transferred via breast milk. Providing this compelling evidence motivates women to continue breastfeeding after receiving the vaccine.

Since vaccination is strongly recommended for pregnant women, the passing of COVID-19 antibodies from mother to baby is a positive indication of the potential for immunity to COVID-19.