| Study characteristics |
| Methods |
Prospective cohort study conducted in the UK in several nursing homes during the 1971 to 1972 influenza season; all residents were under constant surveillance. Throat swab and paired sera specimens were obtained whenever possible. |
| Participants |
490 nursing homes residents (134 treated and 356 controls, all included in the analysis), 60 years or older |
| Interventions |
Parenteral influenza vaccine: A2/HK/68; B/Vic.98926/70. Matching between vaccine and circulating strains is unknown. |
| Outcomes |
Respiratory illness and pneumonia without definition, deaths from pneumonia |
| Notes |
Very poor description of methods; groups were roughly comparable as age and general health. No information about flu activity and laboratory confirmation |
| Risk of bias |
| Bias |
Authors' judgement |
Support for judgement |
| Allocation concealment (selection bias) |
Unclear risk |
D ‐ Not used |
