Researchers in at least four countries are testing whether the century-old vaccine for tuberculosis can lessen the severity of some COVID-19 cases. The vaccine has been around for over a century but researchers argue it might boost the body's ability to fight off the infection before it gets worse.

In Australia, 4,000 health care workers were injected with the vaccine. Those trial results are still a few months away — but it's hoped the old vaccine could become a new weapon in the war against the disease.

"If we find that the BCG vaccine and its ability to boost the immune system does decrease the severity of COVID-19 [...] we would have something kind of off the shelf that we can use, hopefully, during this pandemic or if there was a second wave," said professor Nigel Curtis of the Murdoch Children's Research Institute in Australia. Curtis is running the trial of the vaccine.

A separate New York study that has not yet been peer-reviewed claims countries with high COVID-19 death rates, such as the U.S., did not have universal BCG vaccination policies. The study says countries that routinely vaccinate against tuberculosis, like South Africa, are faring much better.

Most people in South Africa were injected with the BCG vaccine when they were children. But experts warn this isn't a magic bullet — so they continue to test and screen for COVID-19 throughout South Africa.