‘Current antibody tests not accurate’

PETALING JAYA: Currently available antibody tests may not give an accurate or complete picture of one’s immune response after receiving the Covid-19 jab, say health experts.

Universiti Malaya epidemiologist Prof Datuk Dr Awang Bulgiba Awang Mahmud said the usefulness of antibody testing, or serology testing, after one’s Covid-19 vaccination, remained uncertain for now.

He said various vaccines would elicit specific antibodies which might not be detected in a test not designed for that specific antibody.

For instance, mRNA vaccines such as Pfizer would induce the production of antibodies to the spike protein of the virus, but not antibodies to the nucleocapsid protein.

“As such, a person vaccinated with an mRNA vaccine will not test positive in an antibody test if the test is for antibodies to the nucleocapsid protein.

“Moreover, the level of antibodies depends on the person’s immune system response and how long ago the vaccination was carried out. It is expected that antibody levels will wane over time and it would be wrong to make comparisons directly,” he said in an interview.

He was responding to the use of antibody tests following concerns of whether one had truly received the jab following reports of empty syringes used on vaccine recipients.

Recently, several individuals claimed that they tested negative for antibodies after receiving the Covid-19 vaccine.

Some companies have also been offering a range of tests which they claim are able to detect antibodies after a Covid-19 jab.

The body’s immune system, said Dr Awang Bulgiba, was far more complex and did not depend solely on a high level of circulating antibodies.

“There are the B-cell and T-cell responses which are also important. If vaccination results in adequate numbers of memory cells and T-cells, reinfection will elicit the appropriate response and the person should be able to fight off the infection,” he said.

B-cells and T-cells are major components of the body’s adaptive immune response, with the B-cells producing antibodies to destroy invading viruses and bacteria, and T-cells directly fighting against such pathogens.

Dr Awang Bulgiba said there were local health screening companies which had been offering such antibody tests which would typically cost more than RM100 presently.

“A clear advisory needs to be issued by the health authorities on the appropriateness of these tests and how the test can be interpreted.

“Otherwise, there may be claims of ineffectiveness of the vaccines as a result of antibody testing, which can be detrimental to the vaccination programme,” he said.

Dr Awang Bulgiba also lauded the government’s move to conduct surveillance on the neutralising antibodies, B-cells and T-cells among vaccine recipients.

“This follow-up will aid decision-making on whether third doses will be required, and for which vaccines, and whether antibody testing is required for the future,” he said.

Prof Dr Moy Foong Ming also agreed that current antibody tests should not be used to evaluate a person’s level of protection after vaccination.

Dr Moy, who is from Universiti Malaya’s Social and Preventive Medicine Department, said unless there were new tests capable of detecting the antibodies to specific protein targets, those currently available were unlikely to give an accurate picture of a person’s immune response post-vaccination.

“Until a new Covid-19 antibody test is developed to test the specific viral protein targets by the specific vaccine, the public should not waste time and money on antibody tests,” she said.

Malaysian Society of Allergy and Immunology president Prof Dr Baharudin Abdullah previously said it was unclear whether such a test had any value in determining a person’s immune response post-vaccination.

The Food and Drug Administration of the United States currently does not recommend antibody testing as a means to assess immunity levels after someone has received a Covid-19 vaccination.

“While a positive antibody test result can be used to help identify people who may have had a prior SARS-CoV-2 infection, more research is needed in people who have received a Covid-19 vaccination.

“Test results from currently authorised SARS-CoV-2 antibody tests should not be used to evaluate a person’s level of immunity or protection from Covid-19,” it said.