| Study characteristics |
| Methods |
Prospective cohort study conducted in New York, USA during the 1981 to 1982 influenza season in 26 nursing homes. Comparability between cohorts was assessed by analysis of the underlying conditions of a sample of the population; 62 people with severe organic brain syndrome were excluded; medical records were reviewed. Follow‐up period was 1 November 1981 to 30 April 1982. |
| Participants |
451 residents in nursing home for healthy and ill elderly (225 treated and 226 controls, all included in the analysis); most patients required skilled nursing home care |
| Interventions |
Parenteral influenza vaccine: A/Brazil/78; A/Bangkok/79; B/Singapore/80. Matching between vaccine and circulating strains is unknown. |
| Outcomes |
Symptoms defined and radiologically confirmed pneumonia; death from pneumonia within 60 days from the onset of pneumonia |
| Notes |
Vaccinated participants had very slight excess of underlying conditions; smokers were rare; pneumococcal vaccine was rarely used. The circulating strain was not identified. |
| Risk of bias |
| Bias |
Authors' judgement |
Support for judgement |
| Allocation concealment (selection bias) |
Unclear risk |
B ‐ Unclear |
