Trimming rabies shots

One or two injections of a live-but-disabled rabies vaccine might be enough to stave off the virus, a study in monkeys finds. The vaccine will require further testing, but the early results demonstrate a potent immune response that shot-for-shot far exceeds the one generated by the most commonly used commercial vaccine, scientists report in the Oct. 15 Journal of Infectious Diseases.

The current regimen uses killed rabies virus to engender immunity with five vaccine shots and one shot of antibodies.

Virologist James McGettigan and his colleagues at Thomas Jefferson University in Philadelphia made the new vaccine by removing a key component from a live rabies virus. Without that portion, called the M gene, the virus can’t spread in the body. But the disabled virus still constitutes a live vaccine and retains the ability to infect a cell, enabling it to gin up a more potent immune response, McGettigan says.

The scientists injected four rhesus macaque monkeys with the new vaccine and two others with the standard killed-virus vaccine. All got a booster shot five days later. Blood samples obtained 10 days after the initial vaccination indicated the new vaccine had triggered antibody levels four times as great as the commercial vaccine. After 28 days this difference had jumped to seven-fold.

McGettigan says that the early antibody surge suggests the vaccine would work in people exposed to live rabies. And he suspects that further study will show that one or two shots will suffice.

Before beginning human tests, vaccinated monkeys would need to be exposed to live rabies virus as a critical test, McGettigan says. But the high antibody levels generated by the vaccine indicate it will work. “We know it’s protective,” he says.

The World Health Organization estimates that there are 40,000 deaths from rabies worldwide each year, but some studies suggest this vastly underestimates the actual toll.