Unpredictable mutations found in IBV vaccine

Infectious bronchitis virus (IBV) is a highly infectious avian pathogen that affects the respiratory tract, reproductive systems, gut and kidneys. Researchers at the Pirbright Institute have identified what they describe as unpredictable mutations in IBV vaccines produced in chicken eggs that may be prone to reversion in the field. They compared IBV genomes that had been passaged through eggs more than 100 times to find out which genes are involved in weakening the virus. They discovered mutations occurred throughout the IBV genomes, but nine mutations were found more than once across the viruses.
Erica Bickerton, head of the coronaviruses group at the Pirbright Institute, said: “This shows using egg passages as a means of creating attenuated IBV vaccines produces unpredictable changes in the virus. The presence of so few consistent mutations that may weaken the virus indicates the risk that a vaccine strain generated this way could revert back to a more virulent form in the field. We will use the mutation hotspots that we have identified in this study to inform the development of live attenuated vaccines that are genetically modified in the lab.”