Comparison of the protective efficacy of various strains of mumps vaccine: A study in schools

Background: Since the beginning of the program of immunization of children against measles, mumps and rubella (MMR) in 1987, various outbreaks of mumps have occured in Switzerland with a significant proportion of cases in immunized children. Previous studies have suggested a possible lack of efficacy of the Rubini vaccine strain, which has been much used in this country. Methods: Incidence study of secondary cases of mumps in the schools of Geneva, between March 18th and June 30th 1994. Study population. During the study period, mumps outbreaks have been observed in 10 school classes. After exclusion of the 10 primary cases, the study population comprised 195 children aged 4 to 12 years. Results Raw estimation of vaccine efficacy against mumps was 72.5%. Whereas both the Urabe and Jeryl-Lynn strains showed a significant efficacy the Rubini strain didn't show any significant protective effect After adjustment by Poisson regressions for the confounding I effect of age, efficacy rates and 95% confidence limits were 75.8% (35.6%, 90.9%) for Urabe; 64.7% (10.6%, 86.0%) for Jeryl-Lynn; and 12.4% (-102%, 62.1%) fur Rubini. Conclusion: This study didn't show any protective effect of the Rubini vaccine strain. Furthermore, it demonstrated a statistically significant protective effect of the Urabe and Jeryl-Lynn strains, compared to the Rubini strains. In this conditions the use fo teh Rubini strain should be restricted to situations of confirmed contra-indications to the other vaccinal strains, as long as its protective efficacy is not clearly demonstrated.