ca Maeda 2002.

Methods	Prospective open cohort study assessing the effects of TIV on children. The study took place in Japan between November 1999 and April 2000.
Participants	86 healthy recipients of TIV and 94 aged‐matched controls aged 5 to 83 months. Controls were randomly selected from hospital medical records of healthy infants. Age and sex of participants are described in Table 1. There is no mention of attrition, and age and gender of participants appear evenly matched.
Interventions	TIV containing 200 CCA/mL of A/Beijing/262/95(H1N1), 350 CCA/mL of A/Sydney/5/97(H3N2), and 300 CCA/mL of B/Shandong/7/97. 2 injections were given subcutaneously 14 days apart. Dosage was on sliding scale per age: children < 1 year got 0.1 mL, those aged 1 to 6 years got 0.2 mL, and those > 6 years received 0.3 mL. The comparator was do nothing, as placebo administration was not possible "for ethical reasons".
Outcomes	Serological Immunoassay (rapid test, Directigen Flu‐A; Becton Dickinson, USA), capable of detecting only influenza A Effectiveness Influenza A. Swabs were taken from children reporting to the hospital as instructed with a temperature > 37.8 °C. Follow‐up was from January to April 2000. Safety N/A
Funding Source	Unclear
Notes	The authors conclude that inactivated influenza vaccine reduces the incidence of influenza A virus infection in children aged 2 to 6 years but not in children 6 to 24 months old (as 4 out of 5 infected vaccinees belonged to this group). Selection bias may be at play, as the enrolment procedure is not described, and the study controls only for age and sex. In addition, controls were selected on the basis of medical records, which may mean that the controls had had a recent medical contact (although none of them had been vaccinated in the previous 12 months). Viral circulation and vaccine matching are not described.
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	Matched infants in good health
PCS/RCS‐Comparability	Unclear risk	Matched infants
PCS/RCS‐Assessment of Oucome	Unclear risk	Laboratory
Summary assessments	High risk	Selection bias may be at play, as the enrolment procedure is not described, and the study controls only for age and sex. In addition, controls were selected on the basis of medical records, which may mean that the controls had had a recent medical contact.