Influenza A virus

  • Wild birds, particularly waterfowl, are considered to be a natural reservoir for the influenza A virus.
  • Highly pathogenic bird flu viruses cause classical avian flu in chickens and turkeys leading to 100% mortality.
  • Bird flu viruses possess a zoonotic potential and in rare cases may lead to serious illnesses in humans with a fatal outcome.
  • Pigs may serve as a host for porcine, avian and human influenza viruses. Novel influenza A viruses having pandemic potential may result from the adaptation and exchange of gene segments.

Avian influenza in dairy cows in the United States

vache oeil web.JPG

Infections with highly pathogenic avian influenza virus subtype H5N1 (HPAIV H5N1) clade have been detected at numerous dairy farms in a number of US states. The actual extent of the spread in infected dairy herds in the US is as yet unclear.

The current probability of Switzerland being affected by similar cases is very low.

While the general situation continues to be concerning, we are monitoring events in the US closely. The Institute of Virology and Immunology (IVI) is in regular contact with partners in the US as well as other laboratories in Europe.

Further information is available at:

Research project: vaccination of zoo birds against highly pathogenic avian influenza viruses (H5N1) using a vector vaccine

Krauskopfpelikan2  web

Since 2021, all of Europe has been ravaged by the largest ever epidemic due to highly pathogenic avian influenza viruses of the H5N1 subtype. In addition to domestic poultry, many species of wild birds have succumbed to the virus, putting some populations locally at risk. As avian influenza is an ongoing problem and many of the wild species in zoos cannot be kept appropriately under close quarantine conditions, the plan is to protect these birds by vaccination.

Use of an updated vaccine

Several years ago the IVI developed a vector vaccine based on a non-replicable vesicular stomatitis virus (VSV), in which an essential gene was removed and replaced with a gene from the H5N1 avian influenza virus. This vaccine conferred full protection against H5N1 in vaccinated chickens. The vaccine also allows the simple serological differentiation of vaccinated animals from H5N1-infected animals. The IVI has now adapted its existing vector vaccine using the HA antigen of H5N1 viruses (phylogenetic group currently in circulation.  

Protecting wild birds in zoos  

Once the release application had been approved, vaccination was able to begin in August 2023. Since then, 317 birds of 24 different species have been vaccinated at the Bern Animal Park and Basel Zoo involved. The birds tolerated the vaccine well, with no side effects being observed. Serological tests are currently underway to establish whether they have produced enough antibodies to shield them against infection with highly pathogenic H5N1 viruses. The first reliable results are expected in January 2024. 

Approval of experimental release of a genetically modified vaccine

Authorising authority: Federal Office for the Environment (FOEN), 3003 Bern

B/CH/22/01 (B22001): Application 

Which virus is behind the flu?

oie cendrée web

While all eyes are focused on the SARS-CoV-2 pandemic, another virus currently circulating in Europe hits the poultry industry seriously. Hundreds of thousands of birds had to be culled this winter in order to control this epizootic. The pathogen responsible for this animal disease is an influenza virus. Other influenza viruses cause disease in pigs or “flu” in humans. What is the relationship between these different influenza viruses?

Interview with Dr Gert Zimmer, a virologist at the Institute of Virology and Immunology (IVI) and the University of Bern (PDF, 214 kB, 24.02.2022)

NEWS from IVI on cases in Switzerland 


Last modification 06.05.2024

Top of page