| Study characteristics |
| Methods |
Retrospective cohort study conducted in UK during the 1989 to 1990 influenza season, in the community. Data source was the general practitioner database. Follow‐up period was 1 November 1989 to 15 January 1990. As vaccines used in 1988 and 1989 were antigenically closely related, 2 exposure definitions were used: recently vaccinated and previously vaccinated. |
| Participants |
9391 people who had at least a general practitioner's consultation in previous months (599 treated and 8792 controls, all included in the analysis), 55 years or older |
| Interventions |
Parenteral influenza vaccine: A/Shanghai/1197‐like. Vaccine strains matched the circulating strain. |
| Outcomes |
Death, death or severe respiratory illness, death or any respiratory illness without further specification |
| Notes |
Important epidemic year. The study controls for confounders in analysis: age, gender, health status. Data were stratified by health status: people with minor underlying conditions are considered as healthy. People vaccinated during the previous year are considered as "non vaccinated". Quantitative analysis was also performed. |
| Risk of bias |
| Bias |
Authors' judgement |
Support for judgement |
| Allocation concealment (selection bias) |
Unclear risk |
B ‐ Unclear |
