CAPE TOWN, May 4 (Xinhua) -- Researchers in South Africa on Monday vaccinated hundreds of health workers with a 100-year-old tuberculosis (TB) in clinical trial in response to the COVID-19 pandemic.

TASK, a clinical research organization in Cape Town, conducted the trial at Tygerberg Hospital, an officially-designated COVID-19 treatment center in South Africa.

In the trial, researchers used the cheap TB vaccine to determine if a booster shot of Bacille Calmette-Guerin (BCG) reduces the probability of COVID-19 infection and the severity of the symptoms.

The BCG vaccine, devised at France's legendary Pasteur Institute 100 years ago, is one of the world's oldest and most-trusted immunizations. It is primarily a vaccine against TB, which is often given to infants but also protects against other respiratory tract infections in children and adults.

Since South Africa vaccinates all newborns with BCG, this study aims to determine if BCG re-vaccination reduces the probability of infection with the SARS-CoV-2 virus -- the virus causing COVID-19 -- and/or the severity of symptoms of COVID-19 disease, in a bid to help reduce the consequences of this pandemic, TASK said in a statement.

"The primary objective of this trial is to find out if BCG re-vaccination reduces disease severity, hospital admissions and death in frontline workers with direct patient contact during the pandemic phase of COVID-19," said the statement.

In the trial, BCG booster shots were administered to 250 healthcare workers, while another 250 received a dummy formula, or placebo.

After the vaccination, TASK will regularly follow up with telephonic or electronic interviews to capture events such as SARS-CoV-2 virus infection, respiratory tract infection or hospitalization, and run statistical tests to see if an advantage of BCG re-vaccination can be shown, according to the statement.

The trial mainly focused on health workers because they are most exposed to the virus, TASK said, adding that the results will be made public if they are positive enough.

In addition to South Africa, the Netherlands, Australia and France are also conducting BCG clinical trials.