Studies find little to no immunity to H5N1 avian flu virus in Americans

The American population has little to no pre-existing immunity to the H5N1 avian flu virus circulating on dairy and poultry farms, according to preliminary findings from ongoing testing by the Centers for Disease Control and Prevention (CDC).

In other developments, outbreaks in dairy herds continue to be reported at a steady pace, along with sporadic detections in poultry flocks.

Antibody testing on earlier blood samples

The CDC based its serology findings on blood collected from people in all 10 US regions during two earlier flu seasons—2021-22 and 2022-23.

Scientists challenged the blood samples with the H5N1 virus to gauge if there was an antibody reaction. They found that antibody levels were low in people who were or weren’t vaccinated against seasonal flu, hinting at little to no pre-existing immunity and that most of the population would be susceptible if the virus changed to a form that more easily spreads among people. 

“This finding is not unexpected because A(H5N1) viruses have not spread widely in people and are very different from current and recently circulating human seasonal influenza A viruses,” the CDC said regarding the study findings, which it included in a regular update on its response activities.

The risk to the general public remains low, and so far only three human infections have been reported in connection to the dairy farm outbreaks. All involved people who worked closely with cows.

In late May, federal health officials contracted with CSL Seqirus to fill and finish bulk supplies of one of two candidate H5 virus, enough for 4.8 million doses. The CDC has said the vaccine is a good match to the circulating H5N1 strain.

Globally, the main threat from the 2.3.4.4b clade viruses seems to be to people who have been exposed to infected animals. In a related development, Finland’s health ministry last week announced that it will offer avian flu vaccine to people who may be exposed to the virus, such as poultry and fur-farm workers and veterinarians.

The ministry said it will receive a supply of the vaccine as part of a joint procurement among 15 European Union countries and that vaccination will begin as soon as possible. The vaccine was developed by Seqirus UK, Ltd. 

Dairy herd outbreaks top 100; virus infects more poultry

The US Department of Agriculture (USDA) Animal and Plant Health Inspection Service (APHIS) has confirmed 6 more H5N1 outbreaks in dairy herds, lifting the US total to 102. The latest confirmations involved 5 farms in Colorado and 1 in Iowa.

Also, the Iowa Department of Agriculture and Land Stewardship, in two separate statements, has reported three more outbreaks in dairy herds, two more in Sioux County and one in Plymouth County, both in the northwestern part of the state.

Meanwhile, Minnesota reported another outbreak in commercial poultry, which involves a turkey farm that houses 33,100 birds in Stearns County in the central part of the state, according to APHIS.