Global Vaccine Safety

Statement on adverse events following mumps vaccination

January 2004

The Global Advisory Committee on Vaccine Safety (GACVS) considered a proposal for an international reference laboratory for mumps virus isolates and the development of a mumps vaccine virus strain bank at its ninth meeting in Geneva, Switzerland on December 3-4, 2003. Parotitis and aseptic meningitis have been described as complications of mumps vaccination with Urabe, Leningrad–Zagreb and Leningrad-3 strains of the vaccine but not with the Jeryl–Lynn strain1. GACVS noted that now that all mumps virus strains can be characterized by polymerase chain reaction and nucleotide sequencing, it should be possible to address scientifically a number of unresolved questions regarding vaccine safety. These include defining the molecular determinants of virus attenuation, precise genetic determinants of virulence, safety of vaccines in relation to either pure or mixed virus populations in the vaccine and their antigenicity, determining at what stage point mutations occur in the virus (in passage, during replication in the body, or both), and the presence of sub-variant viruses in different vaccines. The Committee recommended that a hypothesis that single point mutations at certain positions of the haemagglutinin–neuraminidase protein gene region of the genome might be associated with post-vaccination aseptic meningitis should be further investigated. Such knowledge would improve current understanding of genetic and molecular characteristics of strains used for production of mumps vaccines. Moreover, further investigation may help to define the safety and immunogenicity profile of mumps vaccines. If molecular assays could distinguish wild-type from vaccine strains of the mumps virus, it would improve the quality control of existing and future vaccines. GACVS has recommended to WHO that an international reference laboratory for mumps virus isolates from vaccinees should be established.

GACVS also took note of the updated review of the safety of mumps vaccine virus strains, which showed that while existing data show different rates of parotitis associated with the different mumps vaccine strains, the data are insufficient to be extrapolated to differential risks for aseptic meningitis. The Committee had previously considered this review at its June 2003 meeting1, and concluded that risk estimates of vaccine-derived mumps meningitis vary between studies, reflecting differences in study settings and circumstances, and degrees of surveillance. The Committee further concluded that available data are insufficient to distinguish between the safety profile with respect to aseptic meningitis for Urabe, Leningrad-Zagreb and Leningrad-3 strains. If Urabe, Leningrad-Zagreb and Leningrad-3 strain vaccines are being used in mass vaccination campaigns, national immunization programmes need to take into account the potential for clustering of aseptic meningitis following the campaigns.

The GACVS is a scientific advisory body established by WHO to provide a reliable and independent scientific assessment of vaccine safety issues in order to respond promptly, efficiently and with scientific rigour to such issues. Membership includes experts from around the world in the fields of epidemiology, paediatrics, internal medicine, pharmacology and toxicology, infectious diseases, public health, immunology and autoimmunity, drug regulation, and safety.

1WER No. 32, 2003, pp. 282–284

Page last reviewed: 7 January 2009