Safety of mumps vaccine strains
At the request of the immunization Strategic Advisory Group of Experts (SAGE), the committee was asked to update the 2003 comprehensive review of the safety of mumps vaccine strains, paying particular attention to the risk of vaccine-derived meningitis. A review of the safety profile based on an updated literature search and data provided by some vaccine manufacturers was presented to the committee.
Similar to its previous review,5 GACVS noted that cases of aseptic meningitis and estimates of incidence rates have been reported following the use of Urabe, Leningrad–Zagreb, Hoshino, Torii, and Miyahara strains from various surveillance systems and epidemiological studies. Given the variability in the quality of these studies and in the methods used, no clear conclusion on differences in risk between these vaccine strains can be drawn. The data up to now have revealed low rates of aseptic meningitis and no cases of virologically proven meningitis following the use of Jeryl–Lynn and RIT 4385 strains. There is only limited information about the Leningrad-3 strain. No data were available to assess the safety of the S79 strain.
Mass vaccination campaigns using mumps–measles–rubella vaccine that contained mumps vaccine strains associated with an increased risk of aseptic meningitis have resulted in clusters of adverse events that disrupted programmes. Recognition of the clustering of cases of aseptic meningitis has potentially been enhanced during mass immunization campaigns due to increased sensitivity of AEFI surveillance. This has been observed with Urabe and Leningrad–Zagreb strains. As of the date of this meeting, all reported cases of vaccine-derived mumps meningitis have recovered. Some of these were laboratory diagnosed cases and had little, if any, clinically significant disease. Despite the occurrence of these cases, the perceived risk–benefit ratio of utilization of the Urabe and Leningrad–Zagreb mumps vaccines over several years in routine programmes in developing countries has been considered acceptable. However, if mumps vaccine strains that have been associated with an increased risk of aseptic meningitis are to be used in mass campaigns, immunization programmes should implement appropriate strategies for communicating risk and managing cases in order to handle possible reports of clusters of aseptic meningitis.
Further studies undertaken to compare the safety profile of different mumps vaccine strains should be carefully designed to discriminate between potential strain variability and age-specific risk in different populations. Standardization of case definitions and quantification of severity will help in interpreting results.
GACVS is pleased with the steps taken to establish a repository of mumps vaccine virus strains at the National Institute for Biological Standards and Control, Potters Bar, England, and urges the acceleration of work to gain insight into the biological determinants of risk from the different strains. The committee requests to be informed of any new data pertaining to the safety of mumps vaccines so that a better assessment can be made of the risk of aseptic meningitis or other conditions associated with specific strains.