ba‐Mackenzie 2006.

Study characteristics
Methods	Case‐control study carried out in a private school in Lothian, Scotland to evaluate effectiveness of 1 or 2 doses of MMR vaccine
Participants	October to November 2004 Cases (N = 20): virologically confirmed mumps cases Controls (N = 40): participants matched to cases for age, sex, residential status, and country source (UK or other)
Interventions	MMR immunisation with 1 or 2 vaccine doses (no description of composition)
Outcomes	Protective effectiveness of MMR immunisation against virologically confirmed mumps
Funding Source	Government
Notes	This study is at high risk of bias due to the following: the size sample of cases employed was too small to reach statistical significance; poor accuracy in reporting vaccination status by parents of some children; the fact that controls had not had virological test; the absolute lack information about vaccine composition (e.g. strain employed); and the narration done by authors to have matched cases and controls for age, sex, residential status, country source without description of these variables in 2 groups.
Risk of bias
Bias	Authors' judgement	Support for judgement
CCS ‐ case selection	High risk	There was insufficient information.
CCS ‐ control selection	High risk	Controls did not have record of previous mumps infections.
CCS ‐ comparability	High risk	There was insufficient information.
CCS ‐ exposures	High risk	Poor accuracy in reporting vaccination status by parents of some children
Summary Risk of Bias assessment	High risk	We had concerns regarding multiple domains such that our confidence in the result is substantially lowered.