| Study characteristics |
| Methods |
Authors investigated an outbreak in a nursing home in Maryland, USA during the 1980 to 1981 influenza season; residents' medical records were reviewed. Follow‐up period was 8 December 1980 to 13 January 1981. Throat swab and paired sera specimens were obtained from some residents. |
| Participants |
159 nursing home residents, 62 to 100 years old (100 treated and 59 controls, all included in the analysis); most of the residents were chronically ill; risk status did not differ between vaccinees and unvaccinated. |
| Interventions |
Parenteral influenza vaccine: A/Brazil; A/Bangkok; B/Singapore. Vaccine strains matched circulating strains. |
| Outcomes |
Clinically defined ILI (2 case definitions; more specific definition was used: fever + cough or chest congestion), pneumonia without further specification, and case‐fatality rate |
| Notes |
Vaccination was not offered to staff. 36% of the observed deaths during the epidemic period occurred from causes other than flu. Circulating strains: A/Taiwan/1/79‐like, very similar to the vaccine strain A/Bangkok. Isolation attempts for other pathogens were unsuccessful. |
| Risk of bias |
| Bias |
Authors' judgement |
Support for judgement |
| Allocation concealment (selection bias) |
Unclear risk |
B ‐ Unclear |
