Stephen J.LurieMD, PhD, Senior EditorIndividualAuthorJody W.ZylkeMD, Contributing EditorIndividualAuthor
To the Editor: In their Research Letter describing treatment for rabies in a patient with lymphoma, Dr Hay and colleagues1 recommended doubling the dose of rabies vaccine and postponing chemotherapy. However, we believe that several issues surrounding rabies postexposure prophylaxis (PEP) require clasification.
First, an assay for antibodies is used to detect an immune response against rabies virus, not to define protection.2 Therefore, "acceptable" response is a more preferred term than "protective" response. The rapid fluorescent focus inhibition test is the current viral neutralization test of choice for human sera.3,4 The Advisory Committee on Immunization Practices (ACIP) has recommended that complete neutralization of virus at a serum dilution of 1:5 is acceptable.3 The World Health Organization recommends a more conservative level of 0.5 IU/mL (a titer of approximately 1:50 by serum dilution).4 Both of these values are arbitrary laboratory standards and neither equates with protection.
Gibbons RV, Rupprecht CE. Postexposure Rabies Prophylaxis in Immunosuppressed Patients. JAMA. 2001;285(12):1574-1575. doi:10.1001/jama.285.12.1574