ca‐Takla 2014.

Study characteristics
Methods	Retrospective cohort study
Participants	Primary school: 108 students of 5 classes with ≥ 1 mumps
Interventions	MMR (RIT 4385 or Jeryl Lynn strain) vaccine 2 doses ‐ vaccination status was determined by number who received vaccine up to 18 days prior to disease onset in the index case of the retrospective cohort.
Outcomes	A mumps case was defined as a primary school student who was diagnosed by a physician with acute mumps disease (defined as ≥ 2 d of 1‐ or 2‐sided parotidal swelling without any other cause and/or laboratory detection (IgM detection or significant increase of IgG between 2 specimens) and/or a clinical‐epidemiological link) between 12 March and 9 May 2011.
Funding Source	Government
Notes	The cohort was limited to affected classes because students of same class stay in the same classroom for instruction; mixing with other grades is usually limited. A voluntary parent‐administered questionnaire was handed out to the student collecting information on demography and mumps‐related symptoms and complications. Parents were asked to return the questionnaire with a copy of vaccination card. Very small control sample size.
Risk of bias
Bias	Authors' judgement	Support for judgement
PCS/RCS ‐ exposed cohort selection	Low risk	Adequate ‐ representative of the exposed ‐ vaccination card
PCS/RCS ‐ non‐exposed cohort selection	Low risk	Adequate ‐ drawn from the same community
PCS/RCS ‐ comparability	Unclear risk	There is insufficient information.
PCS/RCS ‐ assessment of outcome	Low risk	Only clinical definition
Summary Risk of Bias assessment	Unclear risk	We had concerns regarding at least 1 domain such that some doubt is raised about the results.