One important assumption in case-control studies is that control selection should be independent of exposure. Nevertheless, it has been hypothesized that virus interference might lead to a correlation between receipt of influenza vaccination and increased risk of infection with other respiratory viruses. We investigated if such a phenomenon might affect a commonly used study design to estimate influenza vaccination effectiveness (VE). We searched publications in Medline, PubMed and Web of Science. Twelve studies were identified reporting VE estimates using the test-negative design by three alternative control groups: (1) all patients testing negative for influenza, VEFLU-, (2) patients who tested positive for other respiratory viruses, VEORV+, or (3) patients who tested negative for all viruses tested, VEPAN-. These included VE estimates from 7 countries for all ages from 2003/04 to 2013/14. We observed no difference in vaccination coverage between the ORV+ and pan-negative control groups. A total of 63 VEFLU-, 62 VEORV+, and 33 VEPAN- estimates were extracted. Pooled DeltaVE estimates were very similar between groups. In meta-regression, no association was found between the selection of control group and VE estimates. In conclusion, we did not find any differences in VE estimates based on the choice of control group.
- All age groups
- Coverage
- Efficacy/effectiveness
- Influenza
