Together with RIVM (National Institute for Public Health and the Environment) and the University of Oxford (UK), Nivel has started a research project to assess the impact of influenza vaccination in terms of general practice consultation rates, hospitalizations and mortality: the VIcTOR study. This is an 18-month study funded by ZonMw.
Previous research (2006-2016) has shown that contrary to expectations influenza vaccinees in the Netherlands consult their general practitioner for clinically diagnosed influenza, acute respiratory infections, and pneumonia more often than non-vaccinees. We showed that pattern is consistent in all age groups studied and regardless of whether people had a medical indication for the flu vaccination. Important note: considering the data are not laboratory-confirmed these results cannot be directly linked to influenza, but only to respiratory illnesses in general.
One explanation that may partially explain these findings is that the consultation behavior of persons who are vaccinated is different to those who are not vaccinated (e.g. there is a ‘health seeking’ bias). To assess this factor, we included a control condition in our analysis, namely lower back pain, and we found that people with a flu vaccination visited their GP more often because of lower back pain. This suggests that our findings are partially influenced by the role in consultation behaviors (more frequent GP visits). In order to better explain these findings and to link influenza vaccination to more severe outcomes (hospitalizations and mortality) Nivel has started the VIcTOR study.
For the VicTOR study, different types of data will be linked, both nationally and internationally: general practitioner’s data, hospital admissions data and mortality data. In addition, the control group will be expanded to additional infectious and non-infectious conditions. Finally, this research will also be conducted in England, using the database of the Royal College of General Practitioners. For the 2006-2016 research, that preceded this VIcTOR study, data was used from the Nivel Primary Care Database.
This research project relates to Nivel's research program General Practice Care (lead by Joke Korevaar, PhD).