As SARS-CoV-2, the novel coronavirus that causes COVID-19, continues to spread around the world, so do the concerns of breastfeeding mothers. Although there have been no documented cases to date of an infant contracting COVID-19 as a result of consuming infected breast milk, the critical question of whether there is potential for this form of mother-to-infant transmission remains. Our latest study, published August 19, 2020 in the online edition of JAMA, sought to answer this question.

What did we do? 

Since March 2020, our Mommy’s Milk: Human Milk Biorepository has been collecting breast milk samples by mail from breastfeeding women throughout the U.S. who reported being symptomatic for COVID-19, having been exposed to an infected person, or having a confirmed SARS-CoV-2 infection. In preparation for analyzing these samples, in collaboration with colleagues at the University of California Los Angeles we developed and validated an RT-PCR test (a laboratory technique) for detecting SARS-CoV-2 in breast milk. We also developed a test to determine if any virus found in milk would be able to replicate; the ability of the virus to replicate is a key component of determining whether an infant could be infected by consuming milk that contains the virus. Last, we developed techniques to mimic the type of pasteurization that human milk banks use to screen donor milk for infection; we did this so we could determine if these techniques are able to eliminate any virus in milk. The study was partly supported by Emergency COVID-19 Research Seed Funding provided by the University of California Office of the President.

What did we find? 

Between March 27 and May 6, we enrolled 18 women who had a confirmed SARS-CoV-2 positive test; these 18 women provided a total of 64 breast milk samples that were collected at different time points before and after their positive test result. Of the 64 milk samples that were collected, we only detected virus in one sample; however, subsequent tests found that the virus was unable to replicate. In addition, infectious virus could not be detected in milk samples following pasteurization.

So what’s the take-away? 

According to the lead investigator on this study, director of Mommy’s Milk, and our Center co-Director Dr. Tina Chambers, PhD, MPH: “Detection of virus does not equate to infection. It has to grow and multiply in order to be infectious and we did not find that in any of our samples. Our findings suggest breast milk itself is not likely a source of infection for the infant.” She also added that our pasteurization findings are “a very positive finding for donor milk, which so many infants – especially those born premature – rely on.”

However, she also cautioned that more research is needed: “Our findings fill in some important gaps but more studies are needed with larger sample sizes to confirm these findings.” To that end, our future work will not only look at whether breast milk is free of the virus, but also if it contains active antiviral components, such as antibodies to SARS-CoV-2 that women may produce after exposure to the virus and that they can then give to their infants through breast milk, protecting the infant from COVID-19.

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