aa Weingarten 1988.

Methods	Randomised controlled trial, double‐blind, conducted in the USA during the 1985 to 1986 influenza season. Follow‐up was not indicated. Epidemic influenza was defined according to population surveillance data (without better explanation), begun in December 1985 and concluded in February 1986. Participants were assigned using a random number generator to receive either the influenza vaccine or placebo. Virological surveillance was not performed.
Participants	179 healthy volunteer hospital employees: 91 treated and 88 placebo. Age of participants was 21 to 65.
Interventions	Split trivalent intramuscular vaccine. Schedule and dose were: single dose; 15 µg each strain. Vaccine composition was: A/Chile/1/83 (H1N1), A/Philippines/2/82 (H3N2), and B/USSR/100/83. Placebo was saline for injection. Vaccine was recommended but did not match the circulating strain.
Outcomes	Clinical cases symptoms defined, WDL regardless of cause, and adverse effects. Influenza illness was defined by the CDC case definition: a documented temperature greater than 100 °F and at least the symptoms of cough or sore throat.
Notes	Data regarding WDL and adverse effects were not complete and they were not considered. Most of the influenza infections were caused by type B. Efficacy 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