RESUMEN
A considerable number of field trials have been published over the last 30 years, showing measles vaccines to be highly effective. Due to inconsistencies in methodology, comparisons between these studies have often been difficult with regard to the potencies used and the sero-response of vaccinated children. This article reviews key studies which have measured the response of children to different potencies of vaccine. The review concludes that increasing the titre of vaccine above log10 3.0 does not appear to improve vaccine efficacy. It is recommended that standard titre measles vaccine should be administered with a minimum potency of log10 3.0 TCID50 or PFU per dose at 9 months of age or later. This recommendation is endorsed by the Global Advisory Group and the Research and Development Group of the Expanded Programme on Immunization.