Brazil on Monday began to test the efficacy of Bacillus Calmette-Guerin (BCG) tuberculosis vaccine in treating COVID-19 patients.

State-run research center the Oswaldo Cruz Foundation (Fiocruz) began testing on healthcare workers after the vaccine proved effective in reducing respiratory infections, according to state news agency Agencia Brasil.

Initially, the vaccine will be tested on 2,000 volunteers in Campo Grande, the capital of Mato Grosso do Sul state, and on 1,000 other volunteers in Rio de Janeiro.

The tests are part of a phase III clinical trial that aims to assess whether BCG vaccination can reduce the impact of COVID-19 on healthcare workers, those most exposed to the virus.

In addition to the 3,000 Brazilian volunteers, 7,000 volunteers in Australia, Britain, Spain and the Netherlands will also take part in the trials. All are to be monitored for a year.

BCG vaccine is one of the widely used ones in the world, administered each year to about 120 million newborns. Several studies have shown its effectiveness against other infections in addition to tuberculosis.

Fiocruz said that a clinical study carried out in Greece showed the use of the vaccine in the elderly reduced respiratory infections by 79 percent over a year of follow-up.