Factors influencing the antibody response to vaccination against rabies

Preventive vaccination against rabies virus is a highly effective method for preventing rabies in humans and animals. For travel purposes, vaccination of domestic carnivores is obligatory. In addition, some countries require testing for neutralizing antibodies against rabies. The minimal threshold level accepted by WHO/OIE is 0.5 IU/ml. Despite proper vaccination some animals do not reach the threshold. The objective of this study was to identify specific risk factors in dogs and cats for post-vaccination rabies antibody titres below 0.5 IU/ml by FAVN test. Rabies vaccination protocols and recommendations were reviewed with regard to travel regulations. Comprehensive data was collected on animals tested for rabies antibodies via a questionnaire sent to veterinarians who submitted sera for rabies titration. The questionnaire included data on species, age, sex, breed, vaccine used, date of last vaccination and blood sampling, vaccination history and further medical treatments at time of vaccination. Data on around 1,200 animals was analysed. Most animals older than one year had already received more than one rabies vaccination. The influence of breed and sex on antibody titre seems to be insignificant. Young dogs have a high risk of results below 0.5 IU/ml after their first vaccination. This risk can be minimised by the application of a second vaccination and blood sampling according to the manufacturer's recommendations. An important factor for the test outcome might be the virus strain used in the vaccine.