Vaccines might be contributing to the evolution of “stronger” virus strains, according to a new research performed by an international team of scientists. Their findings have been published in PLOS Biology.
The new study deals with the controversial supervirus theory that dictates that vaccines which do not completely eliminate a disease might trigger viruses to develop new traits making them more resistant to treatment. These are referred to as “leaky vaccines” by the researchers.
On the other hand, vaccines for diseases like measles are regarded as “perfect” because they stimulate lifelong immunity (the opposite of “leaky” vaccines), thereby preventing the diseases from proliferating.
Examples of leaky vaccines are those used to treat diseases like malaria and avian flu which are commonly given to livestock. They do not permanently immunise the subjects. To make matters worse, some diseases can still spread after the death of the host.
The team of scientists led by Andrew Read of Penn State administered leaky vaccines for Marek’s disease – a herpes strain affecting poultry – to chickens. That was how they found that unvaccinated ones who came into contact with vaccinated chicks were infected with a viral strain deemed to be worse.
“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,” said Venugopal Nair, one of the authors.
Andrew Read concluded that it was extremely important for “next generation vaccines” for serious diseases like Ebola not to be leaky. Ebola, for instance, is already deadly enough such that having deadlier forms is to be avoided as much as possible.
Another finding suggests that unvaccinated individuals are at greatest risk.
The researchers therefore favour more widespread vaccination.
“The future challenge is to identify whether there are other types of vaccines used in animals and humans that might also generate these evolutionary risks,” write the authors.