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Holder pasteurization of donated human milk is effective in inactivating SARS-CoV-2

Updated: Sep 30, 2021

Mothers' milk can be lifesaving for the smallest and sickest babies in our neonatal intensive care units. It is the optimal source of nutrition, containing many bioactive components that help stimulate the immune system and act as the first line of defence against respiratory and gastrointestinal tract infections-- infections that infants born with very low birth weights are at a high risk of. This is why pasteurized donor human milk is provided as a standard of care to very low birth weight infants in the hospital while their mothers' milk supply is established or to supplement supply.

In light of the COVID-19 global pandemic, our team, led by Drs. Deborah O'Connor and Sharon Unger, was interested in confirming that the current practices for pasteurizing donor milk using Holder pasteurization would be sufficient to inactivate severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in donated human milk samples.

Past epidemics such as HIV/AIDS have had devastating effects on human milk banking because of perceived risks. In addition to HIV, several viruses including hepatitis and cytomegalovirus can be transmitted through human milk. The good news is that the Holder pasteurization method effectively inactivates these viruses. But what about SARS-CoV-2?


What is Holder pasteurization?

Holder pasteurization aims to remove potentially harmful bacteria by heating contents to 62.5°C (145°F) for half an hour, and then cooling it back down to room temperature.


Study Details:

We worked with the Rogers Hixon Ontario Human Milk Bank to conduct this study. Using aliquoted milk samples from 10 de-identified donors, we spiked samples with SARS-CoV-2. One spiked sample from each donor was pasteurized using the Holder method. A second sample from each mother was held at room temperature for 30 minutes. As a control we also replicated this process with unspiked samples from each donor.

What did we find?

  • We found no virus activity in the SARS-CoV-2–spiked milk samples that had been pasteurized using the Holder method.

  • In the samples that were held at room temperature (not pasteurized), we found a reduction in infectivity of SARS-CoV-2.

What does this mean?

Pasteurizing human milk using the Holder method effectively inactivates SARS-CoV-2. In the event that donated milk contains the virus by either transmission through the mammary gland or contamination by respiratory droplets or skin, Holder pasteurization renders donated milk safe for consumption and handling by caregivers.

Previously frozen, thawed human milk also seems to contain sufficient anti-viral activity to partially reduce the infectivity of SARS-CoV-2 in human milk.


To learn more about our ongoing research investigating SARS-CoV-2 in human milk and the impact of the COVID-19 pandemic on breastfeeding, check out our current research!

To learn more about human milk donation, or to register as a donor, visit our friends at the Rogers Hixon Ontario Human Milk Bank.


This study was published in August 2020 in the Canadian Medical Association Journal. You can read the full article here.


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