US authorities have said the detection of a different strain of avian influenza, the D1.1 genotype, in dairy cows in January is proof that bird flu has now spread from wild birds into cattle twice, in an outbreak that started in late 2023.

The genotype refers to the genetic makeup of a virus, within a group of virus types. In this case, it is the highly pathogenic avian influenza (HPAI) A H5N1.

In March 2024, authorities in the US confirmed the outbreak had originated from genotype B3.13. That type has infected more than 950 cattle herds in 16 US states and spread to Canada.

D1.1 was detected in milk collected as part of a surveillance program launched in December 2024.

Yes, it appears that bird flu from the current US outbreak may have spread beyond North America.

In January, UK authorities confirmed a second human case of H5N1 avian influenza. The first was detected in 2022, the UK Health Security Agency (UKHSA) said.

"The risk of avian flu to the general public remains very low despite this confirmed case," said Susan Hopkins, chief medical adviser at the UKHSA, in a statement on January 27.

But many governments have been buying up vaccine stocks and ramping up precautionary measures in response to the circulating virus.

The bird flu variant outbreak has mainly affected the US, with infections among cattle, people and pets.

Though no cases of direct, human-to-human transmission were recorded up to January 2025, there are concerns the H5N1 variant could be one mutation away from becoming a major public health concern.

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