Scientists have found that pasteurisation inactivates the novel coronavirus in human milk, an advance that could help inform guidelines around safe expressing and storing of milk from Covid-19-infected mothers.

However, the study, published in the Journal of Paediatrics and Child Health, noted that breastfeeding is still safe for mothers with Covid-19, adding that there is no evidence to suggest the novel coronavirus SARS-CoV-2 can be transmitted via breastmilk.

According to the scientists, including those from the University of New South Wales (UNSW) in Australia, the country has five human milk banks which screen donors for diseases, test the milk, and pasteurise it to ensure it is safe for medically fragile babies.

“While there is no evidence that the virus can be transmitted through breast milk, there is always a theoretical risk,” said Greg Walker, lead author of the study from UNSW.

“We’ve seen in previous pandemics that pasteurised donor human milk (PDHM) supplies may be interrupted because of safety considerations, so that’s why we wanted to show that PDHM remains safe,” Walker said.

In the study, scientists experimentally infected small amounts of frozen and freshly expressed breast milk from healthy donors.

“We then heated the milk samples — now infected with SARS-CoV-2 – to 63 degree Celsius for 30 minutes to simulate the pasteurisation process that occurs in milk banks, and found that after this process, they did not contain any infectious, live virus,” Walker said.

“Our findings demonstrate that the SARS-CoV-2 virus can be effectively inactivated by pasteurisation,” he added.

According to the researchers, the experiments simulated a theoretical worst-case scenario.

“The amount of virus we use in the lab is a lot higher than what would be found in breast milk from women who have Covid19 — so we can be really confident in these findings,” Walker added.

Laura Klein, a senior study author, said the purpose of the research was to provide evidence behind what people already expected.

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“Pasteurisation is well known to inactivate many viruses, including the coronaviruses that cause SARS and MERS. These findings are also consistent with a recent study that reported SARS-CoV-2 is inactivated by heat treatment in some contexts,” she said.

The researchers also tested if storing SARS-CoV-2 in human milk at 4 or -30 degree Celsius would inactivate the virus, which they said is the first time a study has assessed the stability of experimentally infected SARS-CoV-2 in human milk under common storage conditions.

“We found that cold storage did not significantly impact infectious viral load over a 48-hour period,” Walker said.

“While freezing the milk resulted in a slight reduction in the virus present, we still recovered viable virus after 48 hours of storage,” he added.

The researchers believe the fact that SARS-CoV-2 was stable in refrigerated or frozen human milk could help inform guidelines around safe expressing and storing of milk from Covid-19 infected mothers.