VIcTOR Study: impact of the national flu vaccination program on influenza-like illness, upper respiratory tract infections and pneumonia (2020-2023)

Duration: Nov 2020 - May 2023


Flu vaccination is important for flu prevention. Recent research, however, shows that vaccinated individuals are more likely to be diagnosed with (without laboratory confirmation) influenza-like illness (IAD), upper respiratory tract infections (BLWI) and pneumonia than unvaccinated individuals. This is troubling, important, and fraught with questions about the severity of infections in vaccinated versus unvaccinated individuals and the possible mechanisms for these results.


The aim is to determine the impact of the flu vaccination on the chance of getting ILI, pneumonia or BLWI and what is the seriousness of these conditions?


An analysis will be done. In addition, for more non-infectious diseases, it is investigated whether vaccinated patients visit their GP more often or less often than non-vaccinated people. Finally, the analyzes are repeated in a large registry of patients in England who contact the general practice; these are the dates of the Royal College of General Practitioners.


  • The findings of our analyses will be published in a scientific journal.
  • We will bundle all these results and discuss them in an expert meeting, in order to better interpret the impact and to think about next steps and the associated communication.
  • We will also organize a meeting with all of the key stakeholders in the Netherlands to discuss the results and their communication to a wider audience.
  • Finally, we will establish a technical working group to see if the analysis methods developed for influenza can be applied to other vaccine-preventable diseases, in particular pneumococcal infections.


We expect that the VIcTOR study will contribute to a better understanding of the impact and effectiveness of influenza vaccination.

Dit project wordt gesubsidieerd door
ZonMw - programme Infectious Disease Control 3 (2019 - 2023)
Dutch National Institute for Public Health and the Environment (RIVM), Netherlands; University of Oxford, United Kingdom