ca‐Ong 2007.

Study characteristics
Methods	Retrospective cohort study carried out in Singapore during a measles outbreak in April to May 2004 in primary 3 and 6 school to evaluate MMR vaccine effectiveness
Participants	Participants of the 5 affected classes in primary 3 degree and primary 6 degree (N = 184) (age 8 to 14 years) out of the school enrolment of 1309 students
Interventions	MMR vaccine (no description). Only 1 dose administered. Data about vaccination (date and type of vaccine administered) were noted in health booklet of each child and confirmed with the National Immunisation Registry.
Outcomes	Measles cases laboratory‐confirmed, defined according to WHO 2001 criteria: "recent absentees who had been clinically diagnosed as measles or who had displayed symptoms and sign characterized by generalized maculopapular rash and fever, with or without cough, coryza or conjunctivitis"
Funding Source	Government
Notes	Very bad reporting
Risk of bias
Bias	Authors' judgement	Support for judgement
PCS/RCS ‐ exposed cohort selection	Low risk	Vaccination status of the cases was obtained from children's booklets and confirmed by National Immunisation Registry.
PCS/RCS ‐ non‐exposed cohort selection	Low risk	Drawn from the same community
PCS/RCS ‐ comparability	Unclear risk	The cohort was limited to affected classes, with a very complex mix of ethnicity.
PCS/RCS ‐ assessment of outcome	Low risk	Measles cases laboratory‐confirmed, defined according to WHO 2001 criteria.
Summary Risk of Bias assessment	Unclear risk	We had concerns regarding at least 1 domain such that some doubt is raised about the results.