A recent study has found no evidence of recently infected mothers transmitting infectious SARS-CoV-2 through breastmilk to their babies.

The study was published in the journal Pediatric Research. The authors found that whilst a low proportion of breastmilk contained COVID-19 genetic material, this did not translate into the presence of infectious replicating viral particles or lead to evidence of clinical infection with SARS-CoV-2 in breastfeeding infants.

Authors from the University of California (California, USA) analysed breastmilk samples from 110 lactating women who donated to the Mommy's Milk Human Milk Biorepository at the University of California, San Diego between March and September 2020. Of the 110 women included, 65 had a positive COVID-19 test, while 9 had symptoms but tested negative, and 36 were symptomatic but were not tested.

Paul Krogstad and colleagues found SARS-CoV-2 genetic material (RNA) in the breastmilk of 7 women (6 per cent) with either confirmed infection or who reported being symptomatic. A second breastmilk sample taken from these 7 women between one and 97 days later did not contain any SARS-CoV-2 RNA.

The authors did not find any infectious SARS-CoV-2 genetic material known as SgRNA, which is an indicator of virus replication, in the 7 breastmilk samples and when culturing other samples. There was no clinical evidence of infection in the infants who were breastfed by the 7 mothers with SARS-CoV-2 RNA in their milk.

The authors cautioned that the sample size was low in this study and may not have captured all the potential factors that would predict the presence of SARS-CoV-2 RNA in breastmilk. However, it was the largest study at this time to analyse breastmilk and provided evidence that breastfeeding from women proven or suspected to have had SARS-CoV-2 infection did not lead to COVID-19 infection in their infants.

Paul Krogstad, the lead author, said: "Breastmilk is an invaluable source of nutrition to infants. In our study, we found no evidence that breastmilk from mothers infected with COVID-19 contained infectious genetic material and no clinical evidence was found to suggest the infants got infected, which suggests breastfeeding is not likely to be a hazard."

The authors concluded that their study added to the evidence that women who were infected with COVID-19 and were breastfeeding their child had no risk of transmitting the virus through their breastmilk.