ca King 2006.

Methods	Prospective cohort study carried out at 24 public elementary schools in Maryland, Texas, and Minnesota and 4 (kindergarten to elementary) in Washington during 2004 to 2005. The study aimed at assessing the effect of a school‐based vaccination programme on the households of children attenders. The schools were divided into 11 clusters, 7 of which had random selection of the intervention school and the other 4 of which were selected in a non‐random way. The remaining schools were controls. Clusters were matched by geographic, ethnic, and social class variables. There was a peak circulation period of influenza around the end of January 2005. Other household members could also have been vaccinated. After the peak week, all households who had children in study schools received an anonymised questionnaire. The text also refers to a post hoc analysis of vaccinated and non‐vaccinated children regardless of school. This appears to be a second study and also appears to imply that some of the "control school children" (as well as the household members) were vaccinated.
Participants	5840 pupils in intervention schools and 9451 in control schools, mainly whites in both arms
Interventions	Live attenuated vaccine (MedImmune) intranasally (not better defined) to all children aged 5 or more or do nothing. Content of the vaccine was that of the 2004 to 2005 season. The paper describes main circulating virus (A/California/7/2004 H3N2) as drifted from the strain in the vaccine (not described).
Outcomes	Effectiveness ILI, school absenteeism, serious harms at 42 days after vaccination Safety Reported in an appendix
Funding Source	Industry
Notes	The authors conclude that "Most outcomes related to influenza‐like illness were significantly lower in intervention‐school households than in control‐school households. (ClinicalTrials.gov number, NCT00192218.)". There are several descriptions of the 2005 peak influenza period, but there is no information on vaccine content, although matching must have been at least incomplete as the text described a drifted circulating variant. There is no clear description of age of children or households, of vaccines, of very major discrepancies in denominators of the possible impact of bias of schools who refused to be controls and refused originally proposed placebos. How did this study achieve a trial registration number? It must be an aborted trial.
Risk of bias
Bias	Authors' judgement	Support for judgement
PCS/RCS‐Selection Exposed cohort	Unclear risk	Insufficient description
PCS/RCS‐Selection Non Exposed cohort	High risk	No description
PCS/RCS‐Comparability	High risk	Insufficient information
PCS/RCS‐Assessment of Oucome	Unclear risk	Self report
Summary assessments	High risk	There is no clear description of age of children or households, of vaccines, of very major discrepancies in denominators of the possible impact of bias of schools who refused to be controls and refused originally proposed placebos.