Protective titres of measles neutralising antibody.

A nation-wide measles outbreak occurred in 1988 in Taiwan. A retrospective cohort study was conducted to define the protective titre of measles neutralising (NT) antibody. Paired sera collected in 1987 and 1988 were available from 190 individuals born in 1984 who had participated in an annual hepatitis B immunisation follow-up from 1986 to 1991. Measles NT titres were quantified using a standardised neutralisation enzyme immunoassay. Measles infection was defined as a >/=4-fold rise in NT titre or seroconversion between paired sera. Symptomatic measles infection was ascribed to individuals who had measles infection and who reported measles-like symptoms between 1987 and 1988. Results demonstrated a dose-response relationship between pre-exposure NT titres and protection against measles infection. 47 of 48 individuals with measles infection in 1988 had pre-exposure NT titres </=1,017 mIU/ml; all 12 symptomatic cases had pre-exposure NT titres </=434 mIU/ml. Eleven vaccinees had pre-exposure NT titres <50 mIU/ml, of whom nine developed asymptomatic infection. The study suggests that measles NT titres >1, 000 mIU/ml may prevent measles infection and NT titres >500 mIU/ml may prevent symptomatic infection but vaccinees with undetectable or low NT titres may not necessarily be susceptible to symptomatic infection. Copyright 2000 Wiley-Liss, Inc.