ca‐Marolla 1998.

Study characteristics
Methods	Retrospective cohort study
Participants	Participants were children born between 1 January 1989 and 31 December 1994, whose parents requested an ambulatory visit by their family paediatrician between 15 May and 30 June 1996. 3050 were enrolled, corresponding to about 40% of the children population in the same age range in care by the 20 paediatricians who participated in the study.
Interventions	During 15 May to 30 June 1996 (period in which the visits were performed), the 20 family paediatricians together with children's parents and by considering the content of medical records filled in a schedule in which the following information was collected: personal data, study titre of both parents, type of trivalent MMR vaccine, date of immunisation, practitioner who administered vaccine, onset of measles or mumps disease, eventual hospital admission, diagnostic criteria used, and the practitioner who diagnosed the disease. For the cases when vaccination status could not be immediately assessed, parents were required to communicate as soon as possible the data contained in vaccination records. During study time, paediatricians received a questionnaire on vaccination modality and how to store and administer it correctly. Out of the 3050 initially enrolled children, 2099 were vaccinated with 1 of 3 MMR commercial preparations, whereas 646 were not vaccinated. A total of 2745 children were included in the effectiveness analysis. The remaining 305 participants were excluded due to receiving monovalent vaccine (167), because schedule was compiled with insufficient detail (124), received vaccine after disease onset (6), or contracted measles or mumps before the 15th month of age. Out of the 2099 vaccinated, 1023 received Pluserix SKB, 747 Morupar Biocine, and 329 Triviraten Berna.
Outcomes	Diseases under investigation were defined as follows: Measles: exanthema lasting for at least 3 days, with fever and/or coryza, and/or conjunctivitis, diagnosed at least 30 days after vaccine administration. Mumps: parotid swelling lasting for at least 2 days diagnosed by a practitioner at least 30 days after vaccine administration. Even if not described, paediatricians who conducted the study considered as cases those corresponding to these definitions from schedule data. Altogether 124 measles cases (10 amongst vaccinated) and 457 mumps cases (251 amongst vaccinated) were observed. 92 (74.2%) measles and 386 (84.5%) mumps cases occurred in the years 1995 to 1996.
Funding Source	Not stated
Notes	Diagnosis of measles and mumps disease was made by paediatricians only on clinical parameters and on the basis of data sampled during interviews and of those present in the medical records. Results were managed by the paediatricians themselves, who were not blind to vaccination status of the children. Mean age at enrolment was not statistically different between not‐vaccinated and pooled vaccinated groups (about 52 months), but the authors do not provide these data (or age stratification) within each vaccine arm (considering age interval and visit time, follow‐up time considered could range from 3 to 75 months). Administered vaccine types varied during the time considered for investigation: Strain (a) Pluserix (Schwarz/Urabe AM9) was more used in the years between 1990 and 1991 and was withdrawn from the market in 1992. ca‐Marolla 1998 Strain (a) Schwarz Strain (b) Morupar (Schwarz/Urabe AM9) in 1995 and 1996. ca‐Marolla 1998 Strain (b) Schwarz Strain (c) Triviraten (Edmonston‐Zagreb/Rubini) was of prevalent use in the years 1992, 1993, and 1994. ca‐Marolla 1998 Strain (c) Edmonston‐Zagreb Exposition to disease and time since vaccination could be very different amongst children, which was not taken into account by evaluating effectiveness.
Risk of bias
Bias	Authors' judgement	Support for judgement
PCS/RCS ‐ exposed cohort selection	Low risk	Secure record ‐ vaccination card ‐ representative of the exposed
PCS/RCS ‐ non‐exposed cohort selection	Low risk	Secure record ‐ vaccination card ‐ drawn from the same community
PCS/RCS ‐ comparability	Low risk	Adequate ‐ homogeneous age amongst participants
PCS/RCS ‐ assessment of outcome	Low risk	Diagnosis of measles and mumps disease was made by paediatricians only on clinical parameters and on the basis of data sampled during interviews and of those present in the medical records.
Summary Risk of Bias assessment	Low risk	Plausible bias is unlikely to have seriously altered the results.