aa Sumarokow 1971.

Methods	Field trial conducted in Russia during the 1968 to 1969 influenza season. Follow‐up lasted the whole epidemic period. The epidemic period was defined as the period of highest influenza morbidity and lasted 11 weeks, from the last 10 days of January to the first 10 days of April. Vaccinations were carried out using coded preparation. Sampling virological and serological survey of ill people was performed.
Participants	19,887 population: 9945 treated and 9942 placebo. Age of participants was 13 to 25.
Interventions	Live allantoic intranasal vaccine. Schedule and dose were: 3 doses. Vaccine composition was not indicated. Placebo was not described. Vaccine was not recommended and did not match the circulating strain.
Outcomes	Clinical cases, deaths, severity of illness. Clinical outcomes were all acute respiratory infections. Laboratory confirmation was obtained on a sample of ill participants by virus isolation or demonstration of seroconversion. Bronchitis, otitis, and pneumonia were considered as complications. Passive surveillance was carried out.
Notes	A first study group with children 3 to 12 years old was excluded. A second study group with participants aged 13 to 25 was included in the analysis. The trial compared 2 live vaccines (allantoic intranasal vaccine and tissue vaccine for oral administration) against placebo. Only intranasal vaccine was included in the analysis. Deaths from flu were not recorded. Circulating strain was A2/Hong Kong/68. Effectiveness data only were extracted. Government funded
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Insufficient description
Allocation concealment (selection bias)	Unclear risk	Insufficient description
Blinding (performance bias and detection bias) All outcomes	Unclear risk	Insufficient description
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	Insufficient description
Summary assessment	Unclear risk	Insufficient description