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Protective titres of measles neutralising antibody
1National Institute of Preventive Medicine, Department of Health, Taiwan (Center for Disease Control, Department of Health, Taiwan. mlee@aviron.com
Abstract:
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, 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.
Insights
Measles neutralising antibody titres above 1,000 mIU/ml may prevent infection, while titres over 500 mIU/ml may prevent symptomatic measles. Low antibody levels in vaccinees do not always indicate susceptibility to severe illness.
Area of Science:
- Immunology
- Epidemiology
- Public Health
Background:
- A nationwide measles outbreak in Taiwan in 1988 highlighted the need to understand protective antibody levels.
- Previous studies lacked precise definitions for protective measles neutralising antibody titres.
Purpose of the Study:
- To determine the protective threshold of measles neutralising (NT) antibody titres against infection and symptomatic disease.
- To analyze the relationship between pre-exposure NT titres and protection during a measles outbreak.
Main Methods:
- Retrospective cohort study of 190 individuals born in 1984, with paired sera from 1987 and 1988.
- Quantification of measles NT titres using a standardised neutralisation enzyme immunoassay.
- Definition of measles infection as a ≥4-fold rise in NT titre or seroconversion.
Main Results:
- A dose-response relationship was observed between pre-exposure NT titres and protection against measles.
- Individuals with measles infection in 1988 (n=48) mostly had pre-exposure NT titres ≤1,017 mIU/ml.
- All 12 symptomatic cases had pre-exposure NT titres ≤434 mIU/ml; 9 of 11 vaccinees with NT titres <50 mIU/ml had asymptomatic infections.
Conclusions:
- Measles NT titres >1,000 mIU/ml may prevent measles infection.
- NT titres >500 mIU/ml may prevent symptomatic measles infection.
- Vaccinees with low or undetectable NT titres may not be susceptible to symptomatic infection, suggesting other protective factors may be involved.