Study: Avian influenza vaccine provides protection against currently circulating avian influenza viruses
A recent study by the Finnish Institute for Health and Welfare shows that the avian influenza vaccine provides protection against the disease caused by the currently circulating avian influenza viruses. In Finland, avian influenza vaccinations have been offered to occupational groups at increased risk of the disease, such as those working with fur animals and poultry, since summer 2024.
The study by the Finnish Institute for Health and Welfare (THL) assessed the immunity induced by the avian influenza vaccine in persons belonging to the vaccine target group.
Avian influenza vaccinations were initiated for those working in high-risk professions, such as fur and poultry farm workers, veterinarians and laboratory workers in the summer of 2024.
They were offered a vaccine authorised by the European Medicines Agency, which was expected to provide protection against avian influenza viruses circulating in Finland and Europe in 2023 and 2024.
In 2023, the highly pathogenic avian influenza virus (H5N1) caused extensive outbreaks in Finland that spread from wild birds to fur farms. During the outbreaks, several people who came into contact with infected animals were exposed to the virus that can cause severe disease in humans.
The same virus has caused extensive outbreaks in poultry around the world and in dairy cattle in the United States. An exceptionally high number of human infections were diagnosed in connection with outbreaks in 2024.
A series of two vaccines produced antibodies that protect against avian influenza
The vaccination series offered to those at increased risk of avian influenza consisted of two vaccine doses, which were recommended to be administered at least three weeks apart. According to THL’s vaccination register, 516 people had received at least one and 444 people two doses of the vaccine by the end of January 2025.
The THL study involved 39 people who provided samples for antibody analysees before the vaccination and after the first and second vaccine doses. Some of the participants in the study (n=9) had received avian influenza vaccines also in previous years.
The study showed that the vaccine induced neutralising antibodies that identified the vaccine virus as well as the avian influenza viruses that caused the outbreaks on fur farms in Finland in 2023 and on dairy farms in the United States in 2024.
One vaccine dose induced antibody levels that are estimated to provide protection against the disease caused by the avian influenza virus in about half of the previously unvaccinated individuals, and two doses induced protective antibody levels in the majority. The results suggest that the vaccine provides protection against currently circulating avian influenza viruses.
For those who had already received one or more avian influenza vaccines in previous years, one dose alone induced high levels of neutralising antibodies. The second vaccine dose no longer increased the antibody levels.
The finding suggests that previous avian influenza vaccines have induced long-lived memory cells that recognise different avian influenza viruses.
“Although the vaccine used in Finland is tailored to the current epidemic situation, vaccination can produce long-lasting memory cells and thus also long-term protection against various avian influenza viruses”, says Merit Melin, Research Manager at THL.
The study also assesses the cell-mediated immunity induced by the avian influenza vaccine and the persistence of immunity in vaccinated persons. More participants will be recruited for the study from the target groups for which THL recommends avian influenza vaccinations this spring, well before the spring migration of birds from epidemic areas in Europe. The target groups of the vaccine will remain mainly the same as before.
The study is carried out in cooperation with the Finnish Food Authority, the University of Turku, the Dutch Erasmus University, the HUS Diagnostic Center and the laboratory centres of the wellbeing services counties.
Human avian influenza infections are rare, but animal infections are increasing in Europe
Avian influenza virus infections in humans are rare but can cause very serious disease.
The avian influenza situation in Finland was calm last year. However, outbreaks in wild birds and poultry in Central Europe increased in the autumn of 2024. This year, the Finnish Food Authority has reported one case of avian influenza in a wild bird in Finland.
As a result of the spring migration of birds, infections are also expected to increase in wild birds in Finland. If the virus spreads to farmed animals, the risk of human exposure also increases.
Further information
Avian influenza (THL, in Finnish)
Avian influenza vaccine (THL, in Finnish)
Merit Melin (study results)
Research Manager
THL
tel. +358 29 524 8903
[email protected]
Erika Lindh (avian influenza situation)
Senior Researcher
THL
tel. +358 29 524 8039
[email protected]
