| Study characteristics |
| Methods |
Prospective cohort study conducted in Japan during the 1998 to 1999 influenza season. Follow‐up period was 1 November 1998 to 31 March 1999. 301 nursing homes were surveyed during an epidemic season; only a few residences had an outbreak of respiratory infections. Reports of illness were provided by study site staff. |
| Participants |
22,462 residents in 301 nursing homes (10,739 treated and 11,723 controls, all included in the analysis), 65 years or older |
| Interventions |
Parenteral influenza vaccine: A/Beijing/262/95; A/Sydney/5/97; B/Mie/1/93. Vaccine strains probably matched circulating strains. |
| Outcomes |
Clinical ILI (any of the following symptoms: fever, runny nose, sore throat, cough, headache, muscle aches, chills, vomiting, decreased activity, irritability, wheezing, pulmonary congestion), hospitalisation due to severe illness, deaths due to influenza |
| Notes |
Poor description of methods, poor definitions; some cases were laboratory confirmed, but number of such cases was not indicated. Groups were comparable as age and gender. Health status was not investigated. |
| Risk of bias |
| Bias |
Authors' judgement |
Support for judgement |
| Allocation concealment (selection bias) |
High risk |
C ‐ Inadequate |
