| Study characteristics |
| Methods |
Retrospective cohort study conducted in Michigan, USA during the 1982 to 1983 influenza season. Authors investigated 7 nursing homes with evidence of flu activity. Throat swab and paired sera specimens were obtained from some residents; medical records. Follow‐up period was 10 December 1982 to 4 March 1983. |
| Participants |
1018 residents in 7 nursing homes with outbreak (548 treated and 470 controls, all included in the analysis) |
| Interventions |
Parenteral influenza vaccine: A/Bangkok/79; A/Brazil/78; B/Singapore/79. Vaccine strains probably matched circulating strains. |
| Outcomes |
Clinically defined ILI (fever 37.8 °C or greater + cough, coryza, or sore throat), X‐ray‐confirmed pneumonia, hospitalisation for ILI, deaths occurring within 2 weeks of onset of ILI. An outbreak was defined by a number of ILI per week that exceeded 10% of the residents. |
| Notes |
Cohorts were comparable as age and level of nursing care. Amantadine was not used. The circulating strain was A/Bangkok/1/79‐like. Laboratory confirmation of influenza A infection was obtained in 3 homes. |
| Risk of bias |
| Bias |
Authors' judgement |
Support for judgement |
| Allocation concealment (selection bias) |
Low risk |
A ‐ Adequate |
