| Study characteristics |
| Methods |
Authors investigated an outbreak in a nursing home, in Atlanta, USA during the 1980 to 1981 influenza season; medical charts and hospital charts were reviewed. Follow‐up period was 12 December 1980 to 21 January 1981. Throat swab and paired sera specimens were obtained from some residents. |
| Participants |
120 nursing home residents (36 treated and 84 controls, all included in the analysis), 47 to 95 years old (median age 80 years). Participants required intermediate and skilled nursing care. |
| Interventions |
Parenteral influenza vaccine: A/Bangkok/1/79; A/Brazil/11/78; B/Singapore/222/78. Vaccine strains probably matched circulating strains. |
| Outcomes |
Clinically defined ILI (fever 37.7 °C or greater or cough in the outbreak period (12 December 1980 to 21 January 1981)), death from ILI. Hospitalisation and pneumonia were also accounted for, but results were not presented by immunisation status. |
| Notes |
No confounders control. The circulating strain was A/Bangkok/1/79‐like. Serological tests were negative for other pathogens. |
| Risk of bias |
| Bias |
Authors' judgement |
Support for judgement |
| Allocation concealment (selection bias) |
Unclear risk |
B ‐ Unclear |
