ALTERNATIVE ROUTES OF MEASLES IMMUNIZATION - A REVIEW

Measles is one of the major causes of childhood mortality in developin g countries, despite current prevention of over 2 million child deaths each year by measles vaccination programmes. New strategies, such as mass campaigns, and possibly new preparations oi measles vaccines, may facilitate further progress in controlling the disease and improving the prospects for its ultimate eradication. To evaluate the potential for non-percutaneous routes oi vaccine administration to improve contr ol, we reviewed studies of serological responses to measles vaccine af ter intradermal, conjunctival, oral, aerosol and intranasal administra tion. The response to intradermal vaccination exceeded percutaneous re sults in only one of eight instances in live studies where such compar isons could be made, often producing substantially lower seroresponses . Further, intradermal administration using a needle and syringe is mo re difficult than subcutaneous vaccination. Alter oral administration of vaccine, less than 50% of children seroconverted in three small stu dies. Intranasal administration has not been studied extensively, but it may be susceptible to interference by upper respiratory infections. Seroconversion after conjunctival administration was very variable, a nd this route was difficult practically in young children. In infants below 9 months oi age, aerosol administration of vaccine resulted in 8 0% or better seroresponse in seven of nine trials, with the Edmonston- Zagreb strain in standard titre doses consistently producing better re sults than the Schwarz strain. However, seroresponses after subcutaneo us administration clearly exceeded those from aerosols oi the same vac cine in four of six comparisons. Several trials noted practical diffic ulties in aerosol administration in young infants. in contrast, older seronegative children generally responded well to aerosol administrati on oi vaccine (above 90% and often 100% seroresponse), regardless of v accine strain and often with surprisingly low estimated retained doses . In each of three studies where it was possible to compare the same v accines given percutaneously and by aerosol to seropositive children, better seroresponses followed aerosols. In older children, aerosols of the Edmonston-Zagreb strain also rather consistently provided better seroresponses than aerosols of the Schwarz strain, with the most notab le differences in seropositive children. Thus; with the possible excep tion of very young infants, the aerosol route is promising and offers several theoretical and practical advantages as well. Further randomiz ed trials should be conducted to evaluate comparative responses to aer osolized, intranasal, and subcutaneous vaccine, especially in those ag e ranges targeted for mass campaigns (most commonly 9 months to 15 yea rs). The development oi improved technology for aerosol delivery of me asles vaccine would greatly advance the potential for wide scale use o i this route, especially in mass campaigns in low income countries. (C ) 1997 The international Association of Biological Standardization.