| Study characteristics |
| Methods |
Prospective cohort study conducted in Japan during the 2001 to 2002 period in the community. Data sources were the general practitioner database and self administered questionnaire. Follow‐up period was 31 December 2001 to 31 May 2002. Unvaccinated participants were matched as closely as possible for sex and age to the vaccinated participants. Laboratory confirmation was performed in 60% of cases. |
| Participants |
4423 mostly community‐dwelling (3520 treated and 903 controls were included in the analysis), 65 to 104 years old |
| Interventions |
Parenteral influenza vaccine: A/New Caledonia/20/99; A/Panama/2007/99; B/Johannesburg/5/99. Vaccine strains matched the circulating strain. |
| Outcomes |
Clinically defined ILI (all of the following symptoms: sudden onset, fever 38 °C or more, cough) |
| Notes |
The influenza season was mild. The study controls for age, sex, and previous vaccinations in analysis. |
| Risk of bias |
| Bias |
Authors' judgement |
Support for judgement |
| Allocation concealment (selection bias) |
Unclear risk |
B ‐ Unclear |
