He is one of 560 volunteers in the trials that began on February 26.

After receiving the first shot of the vaccine produced by the Nanogen Pharmaceutical Biotechnology JSC, Tac had said he felt "normal and had no side effects."

"My blood test results after injection showed that the antibody concentration was very high," he told VnExpress.

"I decided to [volunteer] because I have great confidence in the country's scientists."

As a rule, personal information about volunteers taking part in drug human trials is kept confidential unless they agree otherwise, he said, adding therefore he could cannot reveal whether Deputy Prime Minister Vu Duc Dam, head of the coronavirus task force, has also got a Nanocovax shot.

The deputy PM was with him when he received the first shot.

Nguyen Ngo Quang, deputy head of the Administration of Science, Technology and Training, said the vaccine has succeeded in creating large amounts of antibodies in volunteers and has proven effective against mutant strains too.

The second phase would allow researchers to see how exactly immunogenic Nanocovax is. Volunteers in the second phase could include people aged 65 and above and those with non-severe underlying conditions like hypertension and diabetes, according to the National Research Ethics Committee.

The vaccine is expected to enter its third phase of human trials in May and complete it by the end of the third quarter, three months earlier than scheduled.

Tac said Nanocovax is expected to be granted permission for production in the third quarter.