Ch-ch-ch-ch-Changes: why screening the rabies vaccine is necessary for continued safety

Disclaimer: Rabies virus infection can be fatal if not treated immediately. Currently-available rabies vaccines are safe for humans and animals and provide excellent, long-lasting protection against rabies. Studies like the one described below are important because the results from this research will help make rabies vaccines even safer and more effective.  

Rabies is one of the oldest zoonotic diseases (in other words, a disease transmitted from animals to humans). In ancient times rabies was known as hydrophobia, because mammals infected by the rabies virus were unable to swallow and appeared fearful of water. Rabies is a vaccine-preventable disease, but incomplete vaccine coverage means that rabies kills ~59,000 people each year; the vaccine is only used to protect designated high-risk individuals, or to treat individuals who have already been exposed to the virus. The majority of rabies deaths occur in Africa and Asia, with half of these occurring in children. In developing countries, rabies is frequently transmitted to humans by exposure to dog saliva, whereas in developed countries the smaller number of cases are typically caused by zoonotic transmission from wild animals. For this reason, developed countries vaccinate wild animals against rabies by dropping bait pellets containing a live-attenuated (weakened) rabies vaccine in the wild. The live-attenuated rabies vaccine induces a strong and long-lasting immune response.

Cliquet, et al. wanted to characterize the composition of three live-attenuated rabies vaccines using modern molecular techniques. Almost all live-attenuated rabies vaccines, including the three used in this study, are derived from a strain of the virus known as “Street Alabama Dufferin”, which was isolated from a dog in 1935. These vaccines were developed before the discovery of DNA or the recent revolution in genome sequencing technology. Because virus genome sequences can change or ‘drift’ over time, the scientists wanted to carefully analyze the genome sequences of these vaccine strains to determine how closely they matched the genome of the original 1935 isolate. The authors found that one of the vaccine stocks actually contained two different rabies viruses, whereas the other stocks had minor sub-populations of different strains. Fortunately, all of these minor constituents of the vaccines were attenuated, and had not reverted to a wild, pathogenic strain.

This study was the first to report on the diversity of viral genomes in oral rabies vaccines. This information can be used to inform follow-up studies of the properties of the different viruses that comprise the vaccine, and design of superior live-attenuated viruses for future vaccines with increased efficacy and safety.

Summary written by: Patrick Slaine

To read the full article, please click the following link:

In-Depth Characterization of Live Vaccines Used in Europe for Oral Rabies Vaccination of Wildlife

Florence Cliquet, Evelyne Picard-Meyer, Miroslav Mojzis, Zuzana Dirbakova, Zita Muizniece, Ingrida Jaceviciene, Franco Mutinelli, Marta Matulova, Jitka Frolichova, Ivan Rychlik, Vladimir Celer

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