In recent years, swine flu viruses have changed but have not mixed with flu viruses from humans or birds. To timely detect risks for humans and animals, it is important to continue monitoring swine flu viruses. This is shown by research from RIVM, the Animal Health Service (Royal GD Animal Health Service (Animal Health Service)), Erasmus Medical Center (Erasmus MC medical center (medical center)) and Wageningen Bioveterinary Research (WBVR).
Between 2022 and 2025, RIVM, the GD Animal Health Service (Animal Health Service), Erasmus University Medical Center and Wageningen Bioveterinary Research studied which swine flu viruses circulated on Dutch pig farms and whether they changed. Humans and pigs can be infected with each others flu viruses or those from birds. If a pig has multiple flu viruses at the same time, these viruses could mix into a new flu virus variant. The chance of this is small, but if this virus easily infects humans, many people could get the flu at once. Therefore, it is important to know which flu viruses are circulating in the Netherlands, also among pigs.
Research in pig body materials
With the help of veterinarians, GD collected body materials from pigs, such as nasal mucus and saliva. Researchers from GD tested these materials for flu virus. Between July 1, 2023 and September 16, 2025, they tested 2237 samples of body materials. They found flu virus in 484 samples.
Research on genetic material
For some of the viruses found, the research partners conducted further research on genetic material. They shared the genetic data via an online platform. Currently, data from 251 swine flu viruses are available.
The research on genetic material showed that there is exchange of genetic information between different viruses. This means the viruses are changing. Several times similarities with human flu viruses were found. This means viruses have passed from humans to pigs. No new variants were found in which a swine flu virus had mixed with a human flu virus or bird flu virus.
Protection by medicines and vaccines
For 25 viruses, it was studied how well medicines given to people with severe flu work against them. These medicines also worked well against the tested swine flu viruses. The research also helps to monitor how well vaccines protect against these flu viruses. With this information, vaccines for pigs and vaccines that protect people in a possible pandemic can be adjusted.
Comparison with other countries
Because the viruses are changing, it is important to continue monitoring swine flu viruses. It is also good to compare the viruses found in the Netherlands with those from other European countries, because viruses also spread beyond national borders. The obtained information is exchanged with the World Health Organization (WHO) for vaccine development in the context of pandemic preparedness.