MEASLES IMMUNITY AND RESPONSE TO REVACCINATION AMONG SECONDARY-SCHOOLCHILDREN IN CUMBRIA

The prevalence of antibody to measles virus in 759 children aged 11-18 years attending a secondary school in Cumbria was measured using a sa livary Ige antibody capture assay. Serum IgG antibody levels were meas ured using a plaque reduction neutralization assay in subjects whose s aliva was antibody negative. Vaccination histories were obtained from the child health computer and general practice records. A total of 662 pupils (87 % of those tested) had detectable measles-specific IgG in saliva. Of the remaining 97, 82 provided blood samples and 29 had seru m neutralizing antibody levels above 200 mU/ml. After adjusting for no n-participation rates, the proportion considered non-immune (no IgG in saliva and less than or equal to 200 mIU/ml in serum) was 9% overall, ranging from 6% in vaccinated children to 20% in unvaccinated childre n. Measles-mumps-rubella vaccine was given to 50 children of whom 38 p rovided post-vaccination serum and 32 saliva samples. Thirty (79 %) ha d a fourfold or greater rise in serum neutralizing antibody and 28 (88 %) developed IgG antibody in saliva. Half of the children considered non-immune by antibody testing would have been overlooked in a selecti ve vaccination programme targeted at those without a history of prior vaccination. A programme targeted at all school children should substa ntially reduce the proportion nonimmune since a primary or booster res ponse was achieved in three quarters of previously vaccinated children with low antibody levels and in all unvaccinated children. While it i s feasible to screen a school-sized population for immunity to measles relatively quickly using a salivary IgG assay, a simple inexpensive f ield assay would need to be developed before salivary screening and se lective vaccination could substitute for universal vaccination of popu lations at risk of measles outbreaks. The salivary IgG assay provided a sensitive measure of a booster response to vaccination.