The virus that causes COVID-19 cannot be passed from an infected mother to her baby through her breastmilk, a new study led by researchers from University of Idaho and Washington State University has found.

In fact, breast milk from mothers with COVID-19 contains antibodies that can fight off the virus, researchers found, and nursing mothers can effectively pass those on to the infant.

These antibodies do not just neutralize the virus, said Dr. Michelle McGuire at the University of Idaho, who is one of the lead researchers on the study.

“The antibodies specifically kill SARS-CoV-2,” she said.

Of the breast milk samples analyzed from 18 women with COVID-19, none of those samples contained virus RNA (the ribonucleic acid that encodes the virus’ genome ), and the data support breastfeeding for women with mild to moderate COVID-19 infection.

The research was a long time coming, with McGuire and her colleagues around the country at several universities analyzing samples of breastmilk from mothers who had been diagnosed with mild to moderate COVID-19.

The first paper published from their research this week felt like a collective sigh of relief for McGuire.

“It’s really what we were hoping to find,” McGuire told The Spokesman-Review. “At the beginning of the pandemic, we thought there would be virus in some of the milk.”

There were in fact preliminary studies showing that virus RNA was found in breastmilk, while other studies found that it wasn’t. McGuire and the team of researchers she worked with set out to answer that question more definitively, with meticulous study construction, analysis and sampling a lot of breast milk.

The peer-reviewed study published this week analyzes breast milk and breast skin swabs from 18 women, but more than 60 women participated in the study. McGuire said there are forthcoming publications from their research with the same conclusion.

“This supports the WHO recommendations to continue breastfeeding, which is such a relief because they were making those recommendations before we knew,” McGuire said.

Back in the early months of the pandemic, directives from public health officials and physicians differed for pregnant women. It was unclear if the virus could be passed from mother to child, and if so, how. McGuire and the team of researchers called for volunteers from their study, sending them materials to collect their breastmilk and swab themselves. They would send those samples back to labs, where McGuire and others would analyze them.

McGuire is confident in the study’s results due to how rigorous and meticulous the sampling and analysis were.

Researchers asked participants to also swab their breasts before and after washing them, so those samples could be analyzed for any viral material.

Evidence of the virus RNA was detected on just eight out of 70 breast skin swabs, with only one of those considered to be a conclusive positive result. McGuire noted that they have no evidence that the RNA detected actually was live virus, however.

McGuire thinks the virus detected on breasts could be what other researchers previously found as virus in breast milk in earlier studies. Ultimately, the virus detected on women’s breasts did not affect babies breastfeeding during the study.

“Even though 20% of moms had evidence of virus on their breasts, it didn’t seem to pose a risk to these babies,” McGuire said.

She said that in the women they studied, their babies were not getting COVID-19 or displaying symptoms, so there is no evidence women should be worried.

The study does not suggest that women need to systematically wash their breasts before breastfeeding, but instead “supports existing recommendations for women to take precautions during breastfeeding and/or expression of milk (e.g., practicing respiratory and hand hygiene, cleaning pump parts before and after use) to reduce the potential for viral transmission,” the study says.

If a woman with COVID-19 coughs over her exposed breast, she should wash it before feeding, the study suggests, but otherwise, breastfeeding is safe for women with mild to moderate COVID-19 and for their infants, too.