Scientists think they’ve figured out how to make a century-old tuberculosis vaccine far more protective: Simply give the shot a different way.

In a study with monkeys, injecting the vaccine straight into the bloodstream dramatically improved its effectiveness over the current skin-deep shot, researchers reported. “This offers hope,” although more safety studies are required before human testing, said Dr. Robert Seder of the National Institutes of Health, a senior author of the study.

Tuberculosis kills about 1.7 million people a year. The only vaccine is used mainly in high-risk areas to protect babies from one form of the disease. But it’s far less effective at protecting teens and adults from the main threat, TB in the lungs.

In the new study, researchers at the NIH teamed with the University of Pittsburgh to test a variety of ways to give the TB vaccine, including a mist. Monkeys given today’s standard skin shot, even with a higher dose, were only slightly more protected than unvaccinated animals, and the mist wasn’t too effective, either.

But in 9 of 10 monkeys, a higher-than-usual vaccine dose injected into a vein worked much better, the researchers reported in the journal Nature. The team found no trace of infection in six of the animals and counted very low levels of TB bacteria in the lungs of three.

Associated Press