Ho Chi Minh City's frontline facility in the Covid-19 fight, which simultaneously performs testing and treats coronavirus patients, has been locked down after recording 55 infections.

The cases are all employees of its IT and admin departments.

Nguyen Vinh Chau, the hospital director, told VnExpress on Monday that ever since the Covid-19 pandemic broke out last year, the hospital has focused on setting up a "defensive" system, aiming to prevent infection between Covid-19 patients and also between patients and medics.

Severe Covid-19 patients are treated in a completely separated area where a pressure control and air conduction system is set up to let air move in just one way to reduce the risk of virus transmission, while all medical staff working in this area must isolate themselves and stay at a hotel after work.

The hospital has implemented many solutions to lower the risk of infection for patients undergoing medical examination and treatment for other diseases, including requesting medical declarations, screening, isolating suspected cases, and equipping employees with protective gear, he said.

"However, unlike medics, administrative staff do not come into direct contact with patients and do not have the habit of wearing protective gear," said Chau.

"Besides, they work in closed, air-conditioned and cramped offices, with frequent exchanges, including with clinical and paraclinical departments."

"In addition, employees having meals together at work create the prefect conditions for the virus to spread," the director explained.

The hospital announced Monday that all 55 infected employees had been fully inoculated with two doses of the AstraZeneca Covid-19 vaccine.

The viral load among the 55 infected employees at the hospital is "extremely low," with all in stable condition and free of symptoms like fevers or coughing.

The source of transmission has yet to be identified and it is possible that some employees had contracted the virus outside, resulting in cross-infection among employees.

Chau noted that more than 80 percent of them are completely asymptomatic but still contagious, and because of that, if an employee catches the virus and goes to work while his or her colleagues fail to follow Covid-19 prevention rules, it will easily spread around.

"Therefore, it is not only necessary to raise vigilance among doctors and nurses but tighten prevention control in every single department."

"This is a very profound lesson for us," he said.

Now under lockdown, the hospital still continues treating existing Covid-19 patients.

It has tracked down 96 other employees having direct contact with infected counterparts and isolated them.

HCMC decided on Monday to extend its social distancing period by another two weeks as the city is still dealing with multiple clusters of unknown sources, including the one at the tropical diseases hospital.

The city of 13 million has recorded 923 local infections in Vietnam's latest Covid-19 wave that started late April, standing third in the number of cases in all 40 afflicted localities, after Bac Giang and Bac Ninh provinces in the north.