The rabies vaccine used for post-exposure prophylaxis in humans is a purified inactivated vaccine produced in Vero cells or human diploid cells. What is the minimum neutralising antibody titre considered protective by WHO, and how is it measured?
- A 0.1 IU/mL measured by ELISA
- B 0.5 IU/mL measured by rapid fluorescent focus inhibition test (RFFIT) or fluorescent antibody virus neutralisation (FAVN) ✓
- C 1.0 IU/mL measured by haemagglutination inhibition
- D 10 mIU/mL measured by complement fixation test
Correct answer: B. 0.5 IU/mL measured by rapid fluorescent focus inhibition test (RFFIT) or fluorescent antibody virus neutralisation (FAVN)
Explanation
WHO considers a rabies virus neutralising antibody titre of 0.5 IU/mL or higher in serum to be an adequate immune response. This threshold is measured by virus neutralisation tests: the rapid fluorescent focus inhibition test (RFFIT) or the fluorescent antibody virus neutralisation (FAVN) test. These assays measure the ability of patient serum to neutralise live rabies virus in vitro, making them the gold standard for assessing rabies immunity.
Reference: WHO Expert Consultation on Rabies, Third Report, 2018 ed.
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