ca‐Schlegel 1999.

Study characteristics
Methods	Retrospective cohort study ‐ Switzerland
Participants	Participants were children aged 5 to 13 years from a small village in Switzerland (n = 165). Vaccination coverage in this population was high (95%).
Interventions	Immunisation with MMR vaccine prepared with different mumps strain. 79 children were immunised with Rubini‐containing MMR vaccine, 36 with Jeryl Lynn‐containing MMR vaccine, and 40 with Urabe‐containing MMR vaccine. 8 participants were not MMR vaccinated. Vaccine strain was unknown for 2 children without mumps, who were excluded from the study. Vaccination status was ascertained by study investigators from vaccination certificates. All children received immunisation within 2 years of age.
Outcomes	A mumps case was defined by viral isolation of mumps virus in a culture, doctor's confirmation of diagnosis, or if the presence of the typical clinical picture was described in a sibling of a patient with confirmed disease. Investigators who ascertained mumps cases were blind to vaccination status. The absence of IgG antibodies to mumps virus served as confirmation of full susceptibility to mumps in non­vaccinated children without clinical signs of the disease.
Funding Source	Government
Notes	Many study details are insufficiently described in this brief report (e.g. mumps case definition, onset and duration of the outbreak, methods of cases ascertainment).
Risk of bias
Bias	Authors' judgement	Support for judgement
PCS/RCS ‐ exposed cohort selection	Low risk	Vaccination status was ascertained by study investigators from vaccination certificates.
PCS/RCS ‐ non‐exposed cohort selection	Low risk	The absence of IgG antibodies to mumps virus served as confirmation of full susceptibility to mumps in non­vaccinated children without clinical signs of the disease.
PCS/RCS ‐ comparability	Unclear risk	No information
PCS/RCS ‐ assessment of outcome	Low risk	The person who investigated the cases of mumps was blinded with regard to the vaccination status.
Summary Risk of Bias assessment	Unclear risk	We had concerns regarding at least 1 domain such that some doubt is raised about the results.