RISK OF ASEPTIC-MENINGITIS AFTER MEASLES, MUMPS, AND RUBELLA VACCINE IN UK CHILDREN

Cases of aseptic meningitis associated with measles/mumps/rubella vacc ine were sought in thirteen UK health districts following a reported c luster in Nottingham which suggested a risk of 1 in 4000 doses, substa ntially higher than previous estimates based on cases reported by paed iatricians (4 per million). Cases were ascertained by obtaining vaccin ation records of children with aseptic meningitis diagnosed from cereb rospinal fluid samples submitted to Public Health Laboratories or disc harged from hospital with a diagnosis of viral meningitis. Both method s identified vaccination 15-35 days before onset as a significant risk factor and therefore indicative of a causal association. With both, h alf the aseptic meningitis cases identified in children aged 12-24 mon ths were vaccine-associated with onset 15-35 days after vaccine. The s tudy confirmed that the true risk was substantially higher than sugges ted by case reports from paediatricians, probably about 1 in 11 000 do ses. However, the possibility that the aseptic meningitis induced by v accination was largely asymptomatic and a chance laboratory finding in children investigated for other clinical conditions, particularly feb rile convulsions, could not be excluded. Comparison of national report s of virus-positive mumps meningitis cases before and after the introd uction of this vaccine indicated that the risk from wild mumps was abo ut 4-fold higher than from vaccine. Altogether, 28 vaccine-associated cases were identified, all in recipients of vaccines containing the Ur abe mumps strain. The absence of cases in recipients of vaccine contai ning the Jeryl Lynn strain, despite its 14% market share, suggested a higher risk from Urabe vaccine. A prospective adverse event surveillan ce system using the study methods is currently being established to as sess the risk, if any, from the Jeryl Lynn strain which is now the onl y mumps vaccine used in the UK.