In the first phase of human trials for Covivac, the second Vietnamese-made Covid-19 vaccine to be tested on humans, 120 volunteers are needed.

Those volunteers will be divided into four groups depending on age and sex. The groups are women aged 18-39, men aged 18-39, women aged 40-59, and men aged 40-59.

The Institute of Vaccines and Medical Biologicals (IVAC), which produces the vaccine, is currently facing a shortage in middle-aged volunteers, said Vu Dinh Thiem, director of the Center for Clinical Trials under the National Institute of Hygiene and Epidemiology.

Thus far, only 19 women and 33 men from the 40-59 age range have registered for the trial.

Thiem said the number of registered volunteers must be twice to thrice more than demanded, because they will be screened before being selected.

For now, the vaccine producer said it prefers volunteers living in Hanoi to ensure ease of monitoring after the vaccination, which will be administered at Hanoi Medical University.

As planned, volunteers would remain at the university for 24 hours following inoculation to ensure the absence of side effects.

Later, they would have their health checked nine times over 13 months since the date they were chosen for the trial, including the first screening to ensure their suitability.

Pre-clinical studies in India, the U.S. and Vietnam have shown Covivac is safe and effective, Minister of Health Nguyen Thanh Long said last week.

Duong Huu Thai, head of the IVAC, said a dose of the vaccine, which has proven effective against the new variants from the U.K. and South Africa, would cost around VND60,000 ($2.60).

Scientists are currently studying its efficacy against more strains, he added.

Vietnam had last month started the second phase of human trials of Nanocovax, the nation’s first Covid-19 vaccine produced by Nanogen Pharmaceutical Biotechnology JSC.

The nation has commenced large-scale vaccination after receiving 117,600 doses of 30 million it had ordered from British-Swedish firm AstraZeneca.

The first doses have been administered to those working on the front lines like medical workers, contact tracers and officials on Covid-19 prevention and control committees.

The government has said it is stepping up negotiations with vaccine manufacturers in the U.S., Russia and some other countries to ensure it could obtain a total 150 million doses this year to cover 70 percent of its population.