The flu epidemic in the winter of 2014 / 2015 lasted 21 weeks and as such was the longest epidemic ever recorded in the Netherlands. Nearly two million people suffered from flu-like symptoms. About 10,000 people were hospitalised for complications from flu, such as pneumonia. During the flu epidemic period, more than 65,000 persons died in the Netherlands; this is approximately 8,600 persons more than the expected number of deaths in this 21-week period. This excess mortality may be associated with the flu. These are the results of the RIVM annual report on influenza and other respiratory infections. The annual report lists the results of the ongoing surveillance and research that RIVM carries out in collaboration with partners to closely monitor developments in the field of respiratory infections to enable timely appropriate measures.

Flu vaccine less effective than anticipated

People over sixty and those with chronic medical conditions such as asthma, are offered an annual flu vaccine. Because flu viruses are constantly changing, the vaccine is developed anew each year. Of the two types of the influenza virus important for humans (type A and type B), influenza virus type A(H3N2) was mainly found at the beginning of the 2014/2015 season. Later in the season influenza virus type B dominated. A part of the influenza type A viruses was found to mismatch with the type A strain in the flu vaccine. Hence the flu vaccine was less effective than expected in that season. It cannot be determined with certainty to what extent this factor contributed to the long duration of the epidemic and the increased number of deaths during this period. 

(Inter)national collaboration for appropriate measures

The report of RIVM on the facts and figures about the flu virus is established by input from various parties:

  • NIVEL keeps track of the number of people visiting their GP with flu-like symptoms and takes care of taking samples from patients
  • On people report flu-like symptoms

  • The CBS reports the number of deaths

  • Erasmus Medical Center provides a detailed analysis of the viruses

  • from laboratory results obtained from Dutch hospitals it is determined how often the flu virus is recorded

RIVM collects these data in order to take appropriate measures and to advise on the prevention and treatment of influenza. Moreover, they report weekly to the health organisations WHO and ECDC for the purpose of establishing international policy. 

For the upcoming flu season several important new collaborations will commence. Jeroen Bosch Hospital and the Leiden University Medical Center together with RIVM will register severe acute respiratory infections for which hospitalisation is required. RIVM will also be part of 24 organisations from 16 European countries that jointly research the efficacy and impact of the flu vaccine in the elderly. 

More information

Annual report on respiratory infectious diseases 2014/2015

Infographic 'Influenza in winter of 2014 / 2015 in the Netherlands – facts and figures'

Infographic  'A graphic summary of flu surveillance'