Publication date

Annual report Surveillance of influenza and other respiratory infections in the Netherlands: winter 2017/2018.

Reukers, D.F.M., Asten, L. van, Brandsema, P.S., Dijkstra, F., Donker, G.A., Gageldonk-Lafeber, A.B. van, Hooiveld, M., Lange, M.M.A. de, Marbus, S.D., Teirlinck, A.C., Meijer, A., Hoek, W. van der. Annual report Surveillance of influenza and other respiratory infections in the Netherlands: winter 2017/2018. Bilthoven: National Institute for Public Health and the Environment, 2018.

Influenza epidemic
The influenza epidemic of the 2018/2019 winter was mild and lasted 14 weeks. That is longer than the average period of nine weeks during the last 20 years, but it is shorter than the extended influenza epidemic of 2017/2018 which lasted 18 weeks. Between October 2018 and May 2019, a total of approximately 400,000 people became ill due to the influenza virus. Approximately 165,000 people consulted their general practitioner with influenza-like symptoms. Fewer people were admitted to the hospital as a result of influenza complications (mostly pneumonia). This number was estimated to be around 11,000, compared to 16,000 during the 2017/2018 flu season. Type A influenza virus was responsible for the majority of illnesses. There were 2,900 more deaths during the influenza epidemic than would normally be expected during this period.

Influenza vaccine effectiveness
During the 2018/2019 flu season, the influenza vaccine in the Netherlands reduced the risk of developing flu by 57%. This is about the same effect as in the previous flu seasons. In Europe, the vaccine was less effective against one of the most common circulating influenza viruses. An international study is being carried out to determine the reason for this. The effectiveness of the influenza vaccine can differ greatly from season to season. This is because the decision on the composition of the flu vaccine is made half a year beforehand. This is based on the viruses that were most common globally during the previous flu season. However, influenza viruses can change or other influenza viruses may dominate by the time the flu season breaks out in the Netherlands. This is why it is not possible to predict exactly which influenza viruses will circulate in the Netherlands in the next season.

Notifiable respiratory infections
Some respiratory infections have to be reported to the Public Health Services. They can then intensively monitor such infections and, if necessary, take timely action to prevent their further spread. The number of reports of legionella increased further in 2018 and reached 584, which is the highest number ever reported. The number of reports of tuberculosis (806), Q fever (18) and psittacosis (64) remained stable. Q fever, psittacosis and legionella generally manifest themselves in the form of pneumonia. The number of cases reported is an underestimation of the actual number. This is because tests are often not carried out for these illnesses if people have pneumonia.