Commonground
Senior Moderator
December 5, 2025
TOKYO -- A University of Tokyo research team announced findings showing that the H5N1 avian flu virus can remain infectious in refrigerated milk from infected cows for over five months.
It is believed that the milk of infected cows has a unique stabilizing effect on the virus, posing the danger of further spreading. Taking appropriate measures, therefore, is crucial.
The team at the University of Tokyo Pandemic Preparedness, Infection and Advanced Research Center (UTOPIA) kept the milk of infected cows at 4 degrees Celsius for over 22 weeks, after which the virus maintained its infectivity and stability. Meanwhile, when the virus was mixed with the milk of uninfected cows, it became undetectable after two to three weeks.
The researchers hypothesized, "It's possible that fat, protein and other components in milk change during infection, potentially protecting the virus."
However, high-temperature pasteurization remained effective even as the virus' stability increased. Heating the milk to 72 degrees Celsius for 30 seconds, standard practice in the U.S., reportedly resulted in the loss of the virus' infectivity.
UTOPIA Director Yoshihiro Kawaoka stated, "Consuming unpasteurized milk could result in infections even to humans. Such a risk persists for a long time with infected cows' milk so we need to consider appropriate countermeasures."
The H5N1 avian flu virus has been spreading globally since 2020, and more mammals are becoming susceptible to it. The fatality rate for humans is estimated to be around 50%. Cases of transmission to dairy cows are increasing in the U.S., causing concern about the virus spreading to humans by way of milk. There are no confirmed cases of the virus being transmitted to cows or humans in Japan.
The team's findings were published in the New England Journal of Medicine.
https://mainichi.jp/english/articles/20251204/p2a/00m/0na/009000c
TOKYO -- A University of Tokyo research team announced findings showing that the H5N1 avian flu virus can remain infectious in refrigerated milk from infected cows for over five months.
It is believed that the milk of infected cows has a unique stabilizing effect on the virus, posing the danger of further spreading. Taking appropriate measures, therefore, is crucial.
The team at the University of Tokyo Pandemic Preparedness, Infection and Advanced Research Center (UTOPIA) kept the milk of infected cows at 4 degrees Celsius for over 22 weeks, after which the virus maintained its infectivity and stability. Meanwhile, when the virus was mixed with the milk of uninfected cows, it became undetectable after two to three weeks.
The researchers hypothesized, "It's possible that fat, protein and other components in milk change during infection, potentially protecting the virus."
However, high-temperature pasteurization remained effective even as the virus' stability increased. Heating the milk to 72 degrees Celsius for 30 seconds, standard practice in the U.S., reportedly resulted in the loss of the virus' infectivity.
UTOPIA Director Yoshihiro Kawaoka stated, "Consuming unpasteurized milk could result in infections even to humans. Such a risk persists for a long time with infected cows' milk so we need to consider appropriate countermeasures."
The H5N1 avian flu virus has been spreading globally since 2020, and more mammals are becoming susceptible to it. The fatality rate for humans is estimated to be around 50%. Cases of transmission to dairy cows are increasing in the U.S., causing concern about the virus spreading to humans by way of milk. There are no confirmed cases of the virus being transmitted to cows or humans in Japan.
The team's findings were published in the New England Journal of Medicine.
https://mainichi.jp/english/articles/20251204/p2a/00m/0na/009000c