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. 2021 May 28;16(5):e0249883.
doi: 10.1371/journal.pone.0249883. eCollection 2021.

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

Saverio Caini  1 , John Paget  1 , Peter Spreeuwenberg  1 , Joke C Korevaar  1 , Adam Meijer  2 , Mariëtte Hooiveld  1
Affiliations

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

Saverio Caini et al. PLoS One. .

Abstract

Introduction: 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.

Methods: 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, ≥75 years) and medical indication for the vaccine (any vs. none, subjects aged ≤60 years only).

Results: 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 ≤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.

Discussion: 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.

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Conflict of interest statement

The authors have declared that no competing interests exist.

Figures

Fig 1
Fig 1. Association between influenza vaccination and the risk of influenza according to age group and presence of medical indication.
Summary risk ratio (SRR) and 95% confidence intervals (CI) were calculated by pooling season-specific risk ratio using random effects meta-analysis models; between-seasons heterogeneity was quantified using the I2 statistics (see text for details; season-specific risk ratio were provided in S1 Table). The Netherlands, seasons 2006/07 to 2015/16.
Fig 2
Fig 2. Association between influenza vaccination and the risk of acute respiratory infection according to age group and presence of medical indication.
Summary risk ratio (SRR) and 95% confidence intervals (CI) were calculated by pooling season-specific risk ratio using random effects meta-analysis models; between-seasons heterogeneity was quantified using the I2 statistics (see text for details; season-specific risk ratio were provided in S2 Table). The Netherlands, seasons 2006/07 to 2015/16.
Fig 3
Fig 3. Association between influenza vaccination and the risk of pneumonia according to age group and presence of medical indication.
Summary risk ratio (SRR) and 95% confidence intervals (CI) were calculated by pooling season-specific risk ratio using random effects meta-analysis models; between-seasons heterogeneity was quantified using the I2 statistics (see text for details; season-specific risk ratio were provided in S3 Table). The Netherlands, seasons 2006/07 to 2015/16.
Fig 4
Fig 4. Association between influenza vaccination and the risk of lower back pain according to age group and presence of medical indication.
Summary risk ratio (SRR) and 95% confidence intervals (CI) were calculated by pooling season-specific risk ratio using random effects meta-analysis models; between-seasons heterogeneity was quantified using the I2 statistics (see text for details; season-specific risk ratio were provided in S4 Table). The Netherlands, seasons 2006/07 to 2015/16.
See this image and copyright information in PMC

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