A plan to carry out the trial had been completed and submitted to the Health Ministry for approval by Hanoi’s Central Lung Hospital in April. It was set to be tested on over 800 medical workers and patients.

While the project had received the nod from several experts, it has been suspended because there are not enough people exposed to Covid-19 right now to evaluate the Bacillus Calmette–Guérin (BCG) vaccine’s effectiveness against the virus, said Nguyen Viet Nhung, director of the Central Lung Hospital.

Instead, researchers would wait for evaluation results from other countries that have undertaken similar trials, such as Australia and the Netherlands, Nhung said.

"The suspension is a thing to be celebrated, because it shows that Vietnam has successfully contained Covid-19," she said.

The trial aimed to find out if the BCG vaccine could limit lung damage on existing Covid-19 patients as also compare symptoms’ severity between those who had BCG vaccinations and those who didn’t.

In March, a preprint published by medRxiv, an online archive and distribution site for complete but unpublished manuscripts in the medical, clinical and related health sciences, founded by Yale University in the U.S. and other stakeholders, showed that countries that widely conducted tuberculosis vaccination had a lower Covid-19 mortality rate.

While medRxiv warned that preprints "should not be relied on to guide clinical practice or health-related behavior and should not be reported in news media as established information," the study has become a basis for several experiments around the world, including in the U.S., Australia and the Netherlands.

No definite conclusion has been drawn on whether the BCG vaccine could effectively protect humans from the novel coronavirus.

In Vietnam, the BCG vaccine has been part of the nation’s immunization program since 1990. Infants get a single shot of BCG vaccine, with medical experts discouraging a second shot citing limited effectiveness seen in further prevention of tuberculosis.

Vietnam has recorded 328 Covid-19 cases so far, and has just 26 active cases left. The country has recorded no community transmission of the virus for the last 49 days.