ca Salleras 2006.

Methods	Prospective cohort study carried out between 1 November 2004 and 31 March 2005 in 11 paediatric clinics in Barcelona, Spain. The study assessed the effectiveness of virosomal vaccine against ILI and its economic consequences.
Participants	966 vaccinated children and 985 non‐vaccinated controls attending respectively 5 and 6 clinics. The unit of selection was clinic enrolment. Children were aged 3 to 14, and age breakdown by exposure, sex, and by 2‐year groupings is reported. Systematic differences are reported (significantly smaller families and younger children in the non‐vaccinated cohort). No attrition is mentioned.
Interventions	1 dose of virosomal influenza vaccine (Inflexal, Berna). Content is not described.
Outcomes	Serological Pharyngeal and nasal swabs sent to laboratory for culture. Follow‐up was by parents' questionnaire. Follow‐up unclear, no mention of how many children were followed up and whether there was attrition in reporting with symptoms. Effectiveness Febrile ARI: fever and respiratory symptoms attended or not by the physician ILI: children seen by physician with fever ≥ 38.5 °C for at least 72 hours, cough and sore throat Influenza (PCR confirmed): as per ILI but with positive PCR Episodes of antibiotic consumption during an acute febrile respiratory illness in the child Episodes of school absenteeism due to an acute febrile respiratory illness in the child Episodes of work absenteeism of a family member taking care of a child with an acute febrile respiratory illness Safety N/A
Funding Source	Industry
Notes	The authors conclude that "Adjusted vaccination effectiveness was 58.6% (95% CI 49.2 to 66.3) in preventing acute febrile respiratory illnesses, 75.1% (95% CI 61.0 to 84.1) in preventing cases of influenza‐like illnesses and 88.4% (95% CI 49.2 to 97.3) in preventing laboratory‐confirmed cases of influenza A. The adjusted vaccination effectiveness in reducing antibiotic use (18.6%, 95% CI ‐4.2 to 3.64), absence from school (57.8%, 95% CI 47.9 to 65.9) and work‐loss of parents (33.3%, 95% CI 8.9 to 51.2) in children affected by an acute febrile respiratory illness was somewhat lower. Vaccination of children aged 3 to 14 years in paediatric practices with 1 dose of virosomal subunit inactivated influenza vaccine has the potential to considerably reduce the health and social burdens caused by influenza‐related illnesses". Systematic differences ("adjusted with logistic regression") between hemicohorts, lack of description of vaccine content, matching and influenza circulation make the conclusions unreliable. Why use PCR? Was the quantity of viral genome so tiny to need amplification?
Risk of bias
Bias	Authors' judgement	Support for judgement
PCS/RCS‐Selection Exposed cohort	Unclear risk	Selected group
PCS/RCS‐Selection Non Exposed cohort	Unclear risk	Same methods but different population
PCS/RCS‐Comparability	High risk	Clearly different populations, no adjustments
PCS/RCS‐Assessment of Oucome	Unclear risk	ILI self reported
Summary assessments	High risk	Some doubt arises from real comparability of the cohort