At 10 a.m. on Tuesday on Reu Island off the northern province of Quang Ninh, Vu Cong Long, the animal farm head at the Center for Research and Production of Vaccines and Biologicals (Polyvac), unlocked the captivity area to feed the monkeys brown rice mixed with black beans and peanuts for lunch.

As he picked up each handful of rice and dropped into a trough, he said, "This diet is very special."

The food has to be clean and does not contain pesticide or chemical residues. Every day the monkeys eat two meals besides fruits and sugarcane to help them eat more and absorb better.

Reu Island is home to over 1,000 rhesus macaques and 12 of them were selected for the trials for the vaccine produced by the Hanoi-based Vaccine and Biological Production Company No. 1 (Vabiotech).

They are aged three to five years, do not suffer from diseases like TB or HIV and stay in individual cages.

The first batch of six monkeys was vaccinated on October 27, and after two months all are healthy. The remaining were vaccinated in early December.

Rhesus macaques are selected for research because they have fewer pathogens, and before being vaccinated the 12 were kept in cages for a month to ensure they were free of diseases.

The number of people they are exposed to is limited to reduce the risk of contracting infections.

Every morning staff check their temperature, eyes for brightness and whether they are active.

If there is any sign of illness, they check for the likely cause and record it in notebooks to report to the vaccine manufacturers and researchers.

One week after vaccination is the critical time since the monkeys could develop side effects.

It requires two or three people to hold down a monkey to check the temperature and injection site for swelling or congestion.

"Luckily, the monkeys are all healthy and can still fight or attack," Pham Xuan Thai, an employee in the lab, said.

Long said, "We have not seen any monkeys showing abnormal signs."

After four months, if the monkey have no abnormal signs or fever, and eat normally, researchers would check their organs for internal damage.

If all the results are acceptable, the process of approval for human trials will begin.

Over 30 years of raising and caring for monkeys Long has not seen any vaccine causing side effects.

Vabiotech is the second Covid-19 vaccine to be tested on monkeys on the island after Nanogen, and both have gone well so far.

Last week Nanogen Pharmaceutical Biotechnology JSC began human trials on three volunteers, who are in stable condition after getting a 25mg dose.

Another 17 received the same dose on Tuesday, and health officials have high expectations for the vaccine.

Polyvac and the Institute of Vaccines and Medical Biologicals (Ivac) are also working on vaccines.

IVAC and Vabiotech’s products are expected to enter human trials in early 2021.

Vietnam also has plans to import vaccines.

Globally 11 vaccines have entered phase three clinical trials.

Vietnam is one of the few countries in Southeast Asia to produce Covid-19 vaccines so far.

It has managed to keep the number of cases down to 1,420 and deaths to 35 in a population of 96 million thanks to its rapid and strict quarantine and tracking measures.