ca‐Barrabeig 2011b.

Study characteristics
Methods	Retrospective cohort study carried out between 1 October 2006 and 15 January 2007 in educational centres (day‐care and preschool centres) in Barcelona, Spain. The objective of this study was to evaluate the direct, indirect, and total effectiveness of measles component of the MMR vaccine in the context of a measles outbreak.
Participants	Children attending day‐care and preschool centres. 1) Children were considered as vaccinated against measles if they had received the MMR vaccine on or after the minimum recommended age for vaccination and at least 14 days prior to the onset of disease in the index case for each educational centre. 2) Susceptible children were defined as non‐vaccinated children without measles infection before outbreak. 3) All children and educational staff who could provide evidence of immunity were either vaccinated with the MMR vaccine or excluded and isolated at home until 21 days after the appearance of rash in the last reported case.
Interventions	MMR vaccine Priorix/Schwarz or MDS/Enders 1 dose at 9 to 12 months. Second dose at 15 months
Outcomes	Confirmed case of measles was defined as laboratory‐confirmed case (positive serology for measles immunoglobulin M antibody by enzyme‐linked immunosorbent assay testing or positive polymerase chain reaction for measles virus in urine sample) or a case that met the WHO clinical case definition and was epidemiologically linked to laboratory‐confirmed case. 1) Direct vaccine effectiveness was estimated from N = 1121 children ≥ 15 months age. 2) Indirect vaccine effectiveness (or herd immunity) was estimated by comparing the risk in non‐vaccinated children from an immunised population and an identical but fully unimmunised population.
Funding Source	Government
Notes	Study conclusion: over 90% of cases in children aged 12 to 14 months would have been avoided by MMR administration at 12 rather than at 15 months.
Risk of bias
Bias	Authors' judgement	Support for judgement
PCS/RCS ‐ exposed cohort selection	Low risk	Adequately defined ‐ vaccination card
PCS/RCS ‐ non‐exposed cohort selection	Low risk	Adequately defined ‐ vaccination card
PCS/RCS ‐ comparability	Low risk	Adequate ‐ age‐specific
PCS/RCS ‐ assessment of outcome	Low risk	Laboratory‐confirmed or WHO clinical case definition
Summary Risk of Bias assessment	Low risk	Plausible bias is unlikely to have seriously altered the results.