Do Australian immunoglobulin products meet international measles antibody titer standards?

The effectiveness of passive immunisation post-exposure to measles appears subject to a dose-response effect. New Zealand and the United Kingdom have increased the recommended dose of polyclonal human immunoglobulin for post-exposure prophylaxis within the last decade in response to concerns about decreasing levels of measles antibodies in these products. This study used the plaque-reduction neutralization test (PRNT) to measure the titer of measles-specific antibodies in Australian immunoglobulin products for post-exposure prophylaxis and compared the utility of an enzyme-linked immunosorbent assay (ELISA) to the PRNT in available Australian and international samples: Australian intramuscular (n = 10), Australian intravenous (n = 28), New Zealand intramuscular (n = 2), Hizentra (subcutaneous)(USA) (n = 3), and Privigen (intravenous)(USA) (n = 2). Measles titres in Australian IM and IV immunoglobulins ranged from 51 to 76 IU/mL and 6 to 24 IU/mL respectively, as measured by PRNT calibrated to the WHO 3 rd international standard. ELISA titres were variable but higher than PRNT titres in all tested samples. Measles antibody titres in Australian immunoglobulin products meet consensus-prescribed international thresholds. Development of a convenient, standardized, readily accessible assay for determination of measles titres in immunoglobulin products would be useful for future studies and facilitate international comparisons.