Impact of influenza vaccination in the Netherlands, 2007–2016: Vaccinees consult their general practitioner for clinically diagnosed influenza, acute respiratory infections, and pneumonia more often than non-vaccinees

• Published in: PloS one Vol. 16; no. 5; p. e0249883
• Main Authors: Caini, Saverio, Paget, John, Spreeuwenberg, Peter, Korevaar, Joke C., Meijer, Adam, Hooiveld, Mariëtte
• Format: Journal Article
• Language: English
• Published: San Francisco Public Library of Science 28.05.2021; Public Library of Science (PLoS)
• Subjects: Age; Asthma; Back pain; Biology and Life Sciences; Cardiovascular diseases; Complications; Computer programs; Coronary artery disease; Diabetes; Diabetes mellitus; Disease; Dosage and administration; Drafting software; Economic impact; Editing; Gastroenteritis; Health risks; Health services; Health surveillance; Heart diseases; Immunization; Impact analysis; Influenza; Influenza vaccines; Laboratories; Long-term care; Low back pain; Medicine and Health Sciences; Methodology; Methods; Morbidity; Older people; People and places; Pneumonia; Population; Primary care; Public health; Respiratory tract infection; Software; Subgroups; Vaccination; Vaccines; Netherlands
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0249883

We aimed to develop an innovative population-based method to estimate the health effect of influenza vaccination based on electronic medical records collected within a general practitioner (GP)-based influenza surveillance system in the Netherlands. In each season between 2006/07 and 2015/16, we fitted multilevel Poisson regression models to compare GP consultation rates for clinically diagnosed influenza, acute respiratory infections (ARI), pneumonia, and lower back pain (as a control) between vaccinated vs. unvaccinated individuals. Season-specific relative risks and 95% confidence intervals (CI) were pooled into summary risk ratio (SRR) through random-effects meta-analysis models. Analyses were stratified by patient age (<45, 45-59, 60-74, [greater than or equal to]75 years) and medical indication for the vaccine (any vs. none, subjects aged [less than or equal to]60 years only). Overall, 12.6% and 21.4% of study subjects were vaccinated because of their age only or because of an underlying medical condition. Vaccine uptake declined over time, especially among subjects aged [less than or equal to]74 years with medical indications for vaccination. Vaccinated individuals had significantly higher GP consultation rates for clinically diagnosed influenza (SRR 1.24, 95% CI 1.12-1.38, p-value <0.001), ARI (SRR 1.33, 95% CI 1.27-1.39, p-value <0.001), pneumonia (SRR 1.27, 95% CI 1.19-1.36, p-value <0.001), and lower back pain (SRR 1.21, 95% CI 1.14-1.28, p-value <0.001) compared to unvaccinated individuals. Contrary to expectations, influenza vaccinees have GP consultation rates for clinically diagnosed influenza, ARI and pneumonia that are 24-33% higher compared to unvaccinated individuals. The lower back pain finding suggests that the increase in consultation rates is partially caused by confounding. Importantly, considering the data are not laboratory-confirmed, our results cannot be linked directly to influenza, but only to respiratory illnesses in general.