| Study characteristics |
| Methods |
Case‐control study conducted in Michigan, USA during the 1989 to 1990 influenza season, in 23 nursing homes. Data sources were: patients specific logs, vaccination records. Follow‐up period was the epidemic period according to surveillance data. Cases developed ILI during the period of laboratory‐confirmed community influenza activity; controls resided in the same facility and were matched for age. |
| Participants |
1198 residents in 23 nursing homes that experienced outbreaks or with virus isolation (361 cases and 837 controls, all included in analysis), 65 years or older |
| Interventions |
Parenteral influenza vaccine; 17% of cases and 17% of controls received pneumococcal vaccination. Vaccine strains matched the circulating strain. |
| Outcomes |
Clinically defined ILI (fever 37.8 °C or greater and 1 or more of the following: cough, sore throat, coryza) |
| Notes |
Circulating strain: A/Shanghai/11/87. The season was an epidemic one. The study controls for confounders in analysis: home size, vaccination level, sex, and age. Quantitative analysis was not performed, as the logistic model used by the authors did not control by health status. |
| Risk of bias |
| Bias |
Authors' judgement |
Support for judgement |
| Allocation concealment (selection bias) |
Low risk |
A ‐ Adequate |
