Breastfeeding may confer protective antibodies against COVID-19 to infants

Breast milk of women with mild-to-moderate COVID-19 illness does not contain SARS-CoV-2 virus, but it carries antibodies against the coronavirus which can confer protection to their breastfed infants, a recent study has shown.

“Taken together, our data do not support mother-to-infant transmission of SARS-CoV-2 via milk,” the researchers highlighted. “These results support recommendations to continue breastfeeding during mild-to-moderate maternal COVID-19 illness as milk likely provides specific immunologic benefits to infants.”

In the prospective study, researchers analysed 37 milk samples from 18 women with COVID-19 (mean age 34.2 years old). [mBio 2021;12:e03192-20]

None of the milk samples contain virus, as indicated by absence of viral RNA based RT-PCR test.

Yet, at least three-quarters of the milk samples contained SARS-CoV-2-specific antibodies — with IgA against the virus detected in 76 percent and IgG found in 80 percent of the milk samples. SARS-CoV-2-specific IgA was consistently present at higher levels than IgG.

When compared with control milk samples collected before the pandemic, the concentrations of anti-RBD* IgA and IgG were significantly higher (p=0.00013 and p=0.03, respectively) in milk samples from these infected participants. 

In addition, 62 percent of the milk samples showed neutralization activity against SARS-CoV-2 infectivity in vitro, whereas such neutralization was not seen in the control milk samples. 

The researchers also collected skin swabs of breast from the participants and analysed them by RT-PCR. Out of the 70 swabs collected, eight samples showed evidence of viral RNA. However, only one of the eight positive results was considered to be conclusive, which the researchers also noted was a swab obtained before breast washing.

“We found evidence of SARS-CoV-2 on the areola/nipple region of several women, but it is unclear whether this RNA reflects viable virus,” they pointed out.

“Our lack of detection of viral RNA on the breast after washing supports existing recommendations for women to take precautions during breastfeeding and/or expression of milk (eg, practicing respiratory and hand hygiene, cleaning pump parts prior to and after use) to reduce the potential for viral transmission,” said the researchers.

“In support of recommendations put forth by the WHO, if a mother who is confirmed/suspected to have COVID-19 has just coughed over her exposed breast, she should gently wash the breast with soap and warm water before feeding,” they explained.

As participants included were cases with mild-to-moderate COVID-19, the researchers could not determine if similar findings would apply to those with more severe disease. “As disease severity may be related to viral titre, it is possible that milk produced by individuals with more severe COVID-19 could contain SARS-CoV-2.”

“It is reassuring that a majority of the infants (83 percent) appeared healthy with no signs of illness, including two whose mothers had detectable viral RNA on their breast skin,” the researchers added.