ab Saxen 1999.

Methods	Randomised controlled trial, double‐blind, conducted in Finland during the 1996 to 1997 influenza season. Randomisation methods were not described.
Participants	216 healthcare workers: 211 treated and 427 placebo
Interventions	Trivalent inactivated intramuscular vaccine. Schedule and dose were: single dose; 15 µg each strain. Vaccine composition was: A/Wahan/359/95, A/Singapore/6/86, and B/Beijing/184/93. Placebo was saline for injection. Vaccine was recommended.
Outcomes	Working days lost due to respiratory infections, episodes of respiratory infections, days ill, and antimicrobial prescriptions. Respiratory infection was a common cold; febrile ILIs were not detected. Local adverse effects were defined as local pain. Systemic adverse effects were defined as fever and fatigue.
Notes	Efficacy data were not extracted because episodes of respiratory infections were unclearly defined. Safety data only were extracted. Government funded
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Unclear
Allocation concealment (selection bias)	Unclear risk	Unclear
Blinding (performance bias and detection bias) All outcomes	Unclear risk	Unclear
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	Unclear
Summary assessment	Unclear risk	Unclear