ba Hirota 1992.

Methods	Case‐control study to asses correlation between ILIs and influenza immunisation status in schoolchildren aged between 6 and 12 years during an epidemic
Participants	814 children from 1 of the 9 elementary schools of Kasuga City (Fukoka Prefecture, Japan). Children were aged 6 to 12 years.
Interventions	Immunisation with commercial inactivated flu vaccine prepared with the strains A/Yamagata/120/86 (H1N1), A/Fukoka/C29/85 (H3N2), B/Nagasaki/1/87. Each mL of vaccine contained 200 CCA units of each strain. Vaccine was subcutaneously administered in 2 doses of 0.3 mL. Vaccination was carried out after consensus from parents was obtained: the first dose was administered on 25 October and the second on 16 November 1988. 496 children (60.9%) were not immunised; 187 (23.0%) received 2 doses of vaccine; and 131 (16.1%) received 1 dose of vaccine. From data recorded by the Surveillance System for Tuberculosis and Infectious Diseases, an influenza epidemic lasted in Fukoka between 30 October and 1 April (with a sharp peak between 25 December and 11 February), which was caused mainly by the strains A/H1N1 (95%), A/H3N2 (3%), and B (2%). Percentages refer to 1575 isolates from all Japan.
Outcomes	Serological N/A Effectiveness Symptoms of ARI: fever (< 37 °C, 37 °C to 40 °C by 0.5 °C intervals), rhinorrhoea, cough, sore throat, nausea or vomiting, diarrhoea, abdominal pain Actions taken due to the symptoms: taking medicine, seeking doctor’s consultation, school absenteeism Gestational age Predisposition: easily inflamed tonsils, liable to get eczema, precedent asthma, allergies Usual dietary intake, gargling, physical exercise, sleeping hours, family composition, passive smoking, numbers of rooms, total room space, window or door sashes, home heating Cases were defined as: MILI (mild influenza‐like illnesses): all individuals with fever 38 °C < 39 °C, with absenteeism and medical consultation SILI (severe influenza‐like illnesses): individuals with fever 39 °C with absenteeism and medical consultation Controls defined as: NS (no‐symptoms group). All those children with no ARI onset, no absenteeism, no medical consultation during the same period (8 January to 11 February 1989) Questionnaires were returned from the parents of 803 children. MILI and SILI groups were composed of 48 and 80 children, respectively. Control group NS consisted of 196 children. Safety N/A
Funding Source	Unclear
Notes	The authors conclude that vaccination was effective against SILI but not MILI ‐ case definition omits ARI onsets during the first 2 weeks of epidemic peak and those after the period (enhances it for the conservative determination for the risk factor). Immunisation data for MILI were not shown. Criteria for selection of case and controls (i.e. absenteeism and medical consultation) might have introduced selection bias.
Risk of bias
Bias	Authors' judgement	Support for judgement
CC‐Case Selection	Unclear risk	Based on self report
CC‐Control Selection	Unclear risk	Not independent from case selection
CC‐Comparability	High risk	No description
CC‐Exposure	Low risk	Secure record
Summary assessments	High risk	Vaccination was voluntary, but its basis was not described.