Thanh, 32, will return to his office next week after staying at home for months under social distancing measures in Ho Chi Minh City.

He has received two Covid-19 vaccine shots but with the city reopening gradually, Thanh wanted guarantees that the vaccine has truly worked and he could engage in public activities with more confidence.

"I had my second jab a month ago but I'm not sure if the vaccine works on me so I had this antibody test done."

It is not difficult for people like Thanh to find an antibody testing service these days. Many clinics in town provide it. He chose a VND300,000 ($13) package at a healthcare facility on Cao Thang Street in District 10.

Thanh got the results of this test after three hours and said he was "quite reassured because the antibody concentration is high."

The provision of the antibody testing service is booming in HCMC, the hardest hit locality by the nation’s fourth and latest Covid-19 outbreak.

Many hospitals have refused to disclose the number of customers they have received for the service.

The cost of antibody testing varies from VND300,000 to VND1.5 million. Some clinics will even send medics over to get blood samples and send the results online or via mail.

At a clinic in Binh Chanh District, an advertisement offers "Covid-19 antibody quantitative test to assess effectiveness of the vaccine."

Its consultant staff said the service would see if the vaccine has created enough immunity to protect the body against Covid-19 or not, and medical staff will go to customers’ houses to collect blood samples and make results available the same day.

At this clinic, the antibody testing service costs VND1.5 million for one customer and VND1.3 million per person if a group of three people buys it.

It recommends that the best time to do the test is 28 days after receiving one dose of Covid-19 vaccine and 14-28 days after receiving two doses.

A private hospital in Cu Chi District also advertises the same service, offering a quantitative antibody test for people who want to know if their bodies have enough antibodies to fight Covid-19 and to know what the concentration of antibodies is after vaccination.

An international hospital in Binh Chanh District has set the price of a walk-in quantitative antibody test at VND350,000. Customers do not have to register in advance for the test. The testing services is provided every day of the week and the result is ready within two hours.

Don't do it

However, both the Health Ministry and the HCMC Health Department have written to related agencies, recommending that the Covid-19 antibody tests are not done.

The ministry and department have argued that it is costly and may foster negligence among people with high antibodies.

According to health authorities, serological tests for antibody detection do not help determine the effectiveness of protection against Covid-19.

This test mainly serves research, epidemiological assessment, and treatment. The World Health Organization (WHO) has not yet issued a recommendation on a protective response threshold for the virus that causes Covid-19, they said.

At a Monday press meet, Nguyen Thi Huynh Mai, office chief of the municipal Health Department, said healthcare units are not banned from conducting the test as the law does not say so, but "scientifically, the Ministry of Health, as well as the Department of Health of HCMC, does not recommend doing an antibody test, because it makes no sense and is an economic waste," she said.

Pham Quang Thai, deputy head of the National Institute of Hygiene and Epidemiology, said no country in the world has recommended the quantitative antibody test after people have received two doses of vaccine, because in the context of mass vaccination, antibody testing will inevitably lead to comparisons between different vaccines.

"No country has proposed antibody testing when deploying large-scale vaccination. It is only used to serve research and treatment to come up with a more comprehensive strategy," he said.

Thai said another reason for not doing a quantitative antibody test is that so far, the standard in antibody testing has not been set to determine which level of antibody concentration is considered a protective threshold and which is optimal.

Each vaccine can help produce different amounts of antibodies, but in addition to stimulating antibody production, vaccines also activate cell-mediated immunity, and having a high amount of antibodies does not necessarily mean it is a good thing and vice versa, he added.

He noted that about 50 percent of people who have been infected with the novel coronavirus have no antibodies or do not have quantifiable antibodies, but they might not get infected again in subsequent exposures, he added.

Thai stressed that a quantitative antibody test is not deemed enough to assess the possibility of a person being protected against Covid-19. This is why the Ministry of Health has not yet recommended the test.

Nguyen Hien Minh, a lecturer at the HCMC University of Medicine and Pharmacy, said the virus that causes Covid-19 can be identified by many different antigens like spike protein antigen (S) and nucleocapsid antigen (N).

For the virus that causes Covid-19, the spike protein (S) plays a decisive role in determining the ability to penetrate cells and most of the testing services on the market now focus on measuring the quantification of IgG antibodies against the S antigen.

"The test would give quick results, but it does not show how well the immune system reacts or how effective it is," Minh said.