Deeks 2011.

Methods	Screening method ‐ to assess vaccine effectiveness of 1 and 2 doses of the MMR vaccine during an outbreak of mumps in Ontario
Participants	The outbreak period was defined as 1 September 2009 to 10 June 2010. Vaccination data on cases occurring during this period were provided by all Ontario health units with confirmed cases of mumps. The 6 health units with the highest incidence of mumps supplied data on vaccine coverage by birth cohort from the Ontario Immunization Record Information System database. Coverage was assessed as of 30 April 2009, as this followed a provincial mumps vaccine catch‐up campaign that targeted students at post‐secondary institutions.
Interventions	MMR vaccination
Outcomes	Effectiveness against mumps
Notes	Results: a total of 134 confirmed cases of mumps were identified. Information on receipt of MMR vaccine was available for 114 (85.1%) cases, of whom 63 (55.3%) reported having received only 1 dose of vaccine; 32 (28.1%) reported having received 2 doses. Vaccine effectiveness of 1 dose of the MMR vaccine ranged from 49.2% to 81.6%, whereas vaccine effectiveness of 2 doses ranged from 66.3% to 88.0%. If we assume vaccine effectiveness of 85% for 2 doses of the vaccine, vaccine coverage of 88.2% and 98.0% would be needed to interrupt community transmission of mumps if the corresponding reproductive values were 4 and 6. Interpretation: the trial authors' estimates of vaccine effectiveness of 1 and 2 doses of mumps‐containing vaccine were consistent with the estimates that have been reported in other outbreaks. Outbreaks occurring in Ontario and elsewhere serve as a warning against complacency over vaccination programmes.