ab Obrosova‐Serova 1990.

Methods	Randomised, single‐blind, placebo‐controlled trial to assess reactogenicity in children of live attenuated cold‐adapted influenza B vaccine
Participants	"The study was conducted in a children's nursery and in a children's boarding school. 109 children and 87 children 3 to 15 years old received respectively vaccine or placebo"
Interventions	Enrolled participants were randomised to receive at least 1 dose or 2 doses of live attenuated cold‐adapted influenza B vaccine derived by reassortment between wild‐type B/Ann Arbor/1/86 and cold‐adapted B/Leningrad/14/55 viruses. First dose of vaccine or placebo was administered at day 0 and second dose after 3 weeks. 0.5 mL vaccine or placebo was administered intranasally by aerosol spray. Placebo consisted of distilled water. At the time of the study no evidence of circulation of influenza B viruses in Moscow was reported to the laboratory responsible for surveillance in the region.
Outcomes	Serological HI titre against LEN‐B/14/5/1 reassortant virus. Sera were collected by finger stick before the first and second inoculations and 3 weeks later. Effectiveness N/A Safety Adverse reactions were defined as fever (axillary temperature > 37.5 °C) and upper respiratory symptoms (coryza or pharyngitis, or both) observed for 4 days after each inoculation.
Funding Source	Government
Notes	The authors conclude that the vaccine was immunogenic in younger children but less so in older children. There was lot of unexplained attrition between the first and second inoculations.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	No description
Allocation concealment (selection bias)	Unclear risk	Not used
Blinding (performance bias and detection bias) All outcomes	Unclear risk	Single‐blinding
Incomplete outcome data (attrition bias) All outcomes	High risk	There was lot of unexplained attrition between the first and second inoculations.
Summary assessments	High risk	There was lot of unexplained attrition between the first and second inoculations.