ANDREW READ, PENN STATE UNIVERSITY
The controversial theory that vaccination against some viruses clears the way for their more-virulent relatives has garnered new support. According to a study published today (July 27) in PLOS Biology, inoculating chickens with a live Marek’s disease virus (MDV) vaccine can lengthen the disease transmission period, allowing stronger strains of the virus to reach unvaccinated birds, effectively increasing the virus’s fitness.
Unlike most human vaccines, the MDV vaccine reduces symptoms of disease, but does not prevent infection or viral shedding, making it what scientists call a “leaky” or “imperfect” vaccine. “Our research demonstrates that the use of leaky vaccines can promote the evolution of nastier ‘hot’ viral strains that put unvaccinated individuals at greater risk,” study coauthor Venugopal Nair, the head of the Avian Viral ...
