| Study characteristics |
| Methods |
Authors investigated an outbreak in a nursing home in California, USA during the 1972 to 1973 influenza season; independent blind assessment was conducted. Follow‐up period was 20 December 1972 to 28 January 1973. Throat swabs were obtained from ill residents. |
| Participants |
392 nursing home residents (204 treated and 192 controls, all included in the analysis). Participants were both ambulatory and bedridden. |
| Interventions |
Parenteral influenza vaccine: A/Aichi/2/62; B/Mass/1/71. Vaccine strains did not match circulating strains. |
| Outcomes |
Clinically defined ILI (fever 37.7 °C + upper respiratory symptoms), laboratory‐confirmed ILI (positive swab culture), deaths from outbreak‐related respiratory illness |
| Notes |
Data stratified by nurse floor. The circulating strain was A/ENG/42/72. |
| Risk of bias |
| Bias |
Authors' judgement |
Support for judgement |
| Allocation concealment (selection bias) |
Unclear risk |
B ‐ Unclear |
