Undermining breastfeeding will not alleviate the COVID-19 pandemic - Authors' reply.

In the ongoing COVID-19 pandemic, questions regarding possible methods of virus transmission, including the safety of breastfeeding by mothers who are infected, are of great importance. We reported the detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) RNA (not viral particles, as incorrectly stated by Natalie Shenker and colleagues) in consecutive milk samples from an infected mother and interpreted our findings with the greatest caution. In particular, we did not claim that SARS-CoV-2 is transmitted via contaminated breastmilk or that breastfeeding should be discontinued by mothers with the infection. Instead, we emphasised that more research is required.

At the time of writing, there are eight other reports of SARS-CoV-2 RNA detection in milk samples, in several cases at multiple timepoints during the course of the infection. Consequently, the now-published review articles that we cited in our Correspondence, which summarised the peer-reviewed publications at the time of submission, are already outdated. In most of these studies, care was taken to avoid environmental contamination (eg, by breast disinfection or washing if feeding occurred before sampling), as also indicated in our Correspondence.

Shenker and colleagues suggest that the detection of SARS-CoV-2 RNA in breastmilk might be the result of retrograde milk flow of infant saliva containing the virus. We feel that this is unlikely; there is no experimental evidence that any virus might be transferred by this route in humans. On the contrary, SARS-CoV-2 contamination from the infant has been excluded in three studies3, 4, 5 reporting viral RNA in milk from mothers, where the infant was either continually COVID-19-negative or separated from the mother, or both. Generally, there are examples of viruses (eg, HIV and human cytomegalovirus) that are shed into breastmilk and might lead to an infection of the neonate, whereas other viruses are shed but typically pose no risk for vertical transmission. Establishing whether either process is relevant for a novel human pathogen requires careful examination.

So far, no cases of SARS-CoV-2 transmission via breastfeeding have been reported, and it has not been established if the virus in this body fluid is infectious. Thus, WHO suggests continuing breastfeeding upon maternal SARS-CoV-2 infection. We agree with this recommendation but feel that further research on this topic to protect neonates and to reassure nursing mothers is highly warranted.