Pace RM, Williams JE, Järvinen KM, et al.

Characterization of SARS-CoV-2 RNA, Antibodies, and Neutralizing Capacity in Milk Produced by Women with COVID-19.

mBio 2021; 12(1).
doi: 10.1128/mBio.03192-20

Since the beginning of the coronavirus disease 2019 (COVID-19), there has been uncertainty and concern regarding mother-to-child transmission via breastfeeding. While there has been uncertainty regarding breastfeeding in the context of COVID-19, it has been well established that breastfeeding reduces the risk of a myriad of short- and long-term infectious and non-infectious disease. Many of these previously seen health benefits are due to passive immunity, which is the passage of pre-made antibodies from mother to child. Prior studies looking at other viral illnesses have shown that mothers are able to provide passive immunity to their child for specific viral illnesses. Despite this passive immunity transmission being documented for other viral illnesses this has not been well studied for COVID-19.

Pace et al. developed a study to first evaluate whether the actual virus that causes COVID-19 illness, severe acute respiratory coronavirus 2 (SARS-CoV-2), can be detected in the milk produced by women recently diagnosed with COVID-19 or on the skin. In addition, they also quantified whether antibodies specific to COVID-19 were detected in the milk collections. Eighteen women with a recent diagnosis of COVID-19 were included in this study and 37 milk samples were evaluated. None of the 37 milk samples from mothers with COVID-19 illness had detectable SARS-CoV-2 identified. Seventy breast skin swabs were taken of the COVID-19 infected mothers and only 8 had detectable SARS-CoV-2 from a swab of the breast skin. Importantly, when looking at passive immunity, 76% of milk samples had a marker for passive immunity IgA, and 80% had the similar passive immunity IgG marker. Overall, there was a higher concentration of IgA than IgG across the milk samples. Of note, 62% of collected milk samples were found to have antibodies against SARS-CoV-2 and thus able to neutralize the virus.

Human milk has been accepted as the best source of nutrition for most infants, although the onset of the COVID-19 pandemic has raised questions regarding these once unified recommendations. We know from this study that there has been no documented transmission of the SARS-CoV-2 in breast milk; however, there was some of the virus detected on skin swabs of the breast. It is important to note that there are antibodies against COVID-19, which are passed in breast milk. Current WHO recommendations, in conjunction with the results from this study, support breastfeeding in women with mild-to-moderate COVID-19 illness. There may also be some benefit to cleansing the breast prior to expressing breast milk. According to this study, breastfeeding presents minimal risk of COVID-19 transmission with potential protective immunity benefit.