New findings in mice have provided hope that a knockout vaccine for rabies that reverses the disease after just one injection may soon hit the market.
The team of American virologists and immunologists, who have engineered the new strain of the rabies virus, say that it induces a far more potent immune response than current vaccines.
They have revealed that in mice already infected with a virulent rabies strain, a single administration of the new vaccine was enough to clear the virus from the body, even after early symptoms had appeared.
The finding attains significance considering that conventional post-exposure rabies vaccines require several injections to produce an appropriate immune response.
Virologist Bernhard Dietzschold and his team at Thomas Jefferson University in Philadelphia, Pennsylvania, say that they wanted to make the new virus strain as safe as an inactivated virus, yet able to rouse the immune response to expunge the infecting virus as quickly as possible.
To make sure the viral strain they developed did not cause disease, they injected it directly into the brains of healthy, but very young, mice.
Pups as young as five days old did not show any signs of rabies.
"This means it's a lot safer than other live attenuated vaccines that are out there," Nature magazine quoted study co-author Craig Hooper, also at Thomas Jefferson, as saying.
Dietzschold and his co-workers then infected adult mice with a virulent strain of rabies virus, injecting the pathogen either into muscle or directly into the brain, and found that their new vaccine could prevent onset of the disease if it was administered within three days of exposure.
"(At present) for humans, we must initiate treatment within 20 hours. We showed we might be able to administer the vaccine later because we can clear the virus even after the onset of early symptoms," he said.
The vaccine also showed its efficacy as a pre-exposure treatment, with mice given the vaccine up to three weeks before being infected with the virus avoiding developing rabies.
"If this proves as safe as we think it is, it could be contemplated as a vaccine where one shot may protect for life," Hooper says.
Dietzschold hopes that further testing may reveal the vaccine's potential for eradicating the disease in dogs, and provide a cheaper and easier alternative to current vaccines for humans.