Voordouw 2003.

Study characteristics
Methods	Retrospective cohort study conducted in the Netherlands during the 1996 to 1997 influenza season, in the community. Data source was the managed care organisation database. Follow‐up period was 1 September 1996 to 1 June 1997. For every individual who had received an influenza vaccination, 1 age‐sex matched unvaccinated control participant was randomly selected.
Participants	17,822 community‐dwelling elderly with a permanent status in 1 of the practices (8911 treated and 8911 controls, all included in the analysis), 65 years or older
Interventions	Parenteral influenza vaccine. Vaccine strain matched the circulating strain.
Outcomes	Influenza as defined by International Classification of Primary Care (R80: proven influenza without pneumonia), pneumonia, deaths from all causes
Notes	The influenza season was relatively mild. Data were stratified by age and health status. Quantitative analysis was also performed only for the outcome 'deaths from all causes'.
Risk of bias
Bias	Authors' judgement	Support for judgement
Allocation concealment (selection bias)	Low risk	A ‐ Adequate

ACS = acute coronary syndromes
CAP = community‐acquired pneumonia
CVA = cerebrovascular accident
HCWs = healthcare workers
ICD = International Classification of Diseases
ILI = influenza‐like illness
NI = neuroaminidase inhibitor
OR = odds ratio
RR = risk ratio
URI = upper respiratory infection
WHO = World Health Organization