CDC: U.S. population Immunity to A(H5N1) clade 2.3.3.4b viruses
CDC analyzed sera collected from people of all ages in all 10 HHS regions. Blood samples were collected during the 2022-2023 and 2021-2022 flu seasons. These samples were challenged with H5N1 virus to see whether there was an antibody reaction. Data from this study suggest that there is extremely low to no population immunity to clade 2.3.4.4b A(H5N1) viruses in the United States. Antibody levels remained low regardless of whether or not the participants had gotten a seasonal flu vaccination, meaning that seasonal flu vaccination did not produce antibodies to A(H5N1) viruses. This means that there is little to no pre-existing immunity to this virus and most of the population would be susceptible to infection from this virus if it were to start infecting people easily and spreading from person-to-person.
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.
