ca Jianping 1999.

Methods	Cohort study carried out on people from the Chinese People's Liberation Army (PLA) between December 1996 and May 1997
Participants	"One hundred and sixty‐eight children aged 3 to 6 years from the PLA in areas not considered at risk and who had not had influenza recently (adult and elderly data not extracted). Vaccinated groups consisted of 80 children aged between 3 and 6 years, 363 adults between 18 and 59 and 235 elderly over 60 years Controls were not immunised. Correspondent groups consisted respectively of 88 (children), 372 (adults) and 218 (elderly) people"
Interventions	Inactivated influenza vaccine Vaxigrip (Pasteur Mérieux Connaught, France). Children up to 3 years were immunised with 2 doses of 0.25 mL administered 1 month apart. A single dose of 0.5 mL was administered to children over 3 years and adults.
Outcomes	Serological N/A Effectiveness All participants were observed from 21 days to 6 months after vaccination. They were asked to report the following symptoms: fever over 38.5 °C, headache, myalgia or arthralgia, cough, sore throat, and coryza. Cases of fever due to other causes were excluded. Influenza‐like syndrome: presence of fever over 38.5 °C and headache, myalgia or arthralgia Common cold: associated with 1 of the following: fever, headache, myalgia or arthralgia, cough, rhinorrhoea, sore throat Upper respiratory tract symptoms: influenza‐like syndrome + common cold Safety Not assessed. Only serious adverse reactions that occurred during the study are reported.
Funding Source	Government
Notes	"The examined vaccine was strongly protective in populations of different ages" The difference between outcomes is unclear. Gender was not considered in the reporting, and it seems strange that children are enrolled in the PLA. May have lost a lot in translation. Very confusing outcome definition and overlap. We have a problem believing that the vaccine protected from the common cold. Viral circulation was not discussed.
Risk of bias
Bias	Authors' judgement	Support for judgement
PCS/RCS‐Selection Exposed cohort	Unclear risk	Insufficient description
PCS/RCS‐Selection Non Exposed cohort	Unclear risk	Insufficient description
PCS/RCS‐Comparability	Unclear risk	Insufficient description
PCS/RCS‐Assessment of Oucome	High risk	Self reported
Summary assessments	High risk	Plausible bias that seriously weakens confidence in the results