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The study confirmed that the true risk was substantially higher than suggested by case reports from pediatricians,probably about 1 in 100,000 doses.However,the possibility that the aseptic meningitis induced by vaccination was largely asymptomatic and a chance laboratory finding in children investigated for other clinical conditions,particularly febrile convulsions,could not be excluded.Comparison of national reports of virus- positive mumps meningitis cases before and after the introduction of this vaccine indicated that the risk from wild mumps was about 4-fold higher than from vaccine.Altogether,28 vaccine-associated cases were identified, all in recipients of vaccines containing the Urabe mumps strain.The absence of cases in recipients of vaccine containing the Jeryl Lynn strain,despite its 14%market share,suggested a higher risk from Urabe vaccine.A prospective adverse event surveillance system using the study methods is currently being established to assess the risk,if any,from the Jeryl Lynn strain which is now the only mumps vaccine used in the UK. |
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