What does an antibody test tell you?

Antibody tests or serological (serum related) tests are done by taking a blood sample. When infected, our immune system produces antibodies to neutralise the virus in the body. These antibodies remain present in the body for some time even after the virus infection is completely eradicated. This helps doctors identify whether the patient was infected earlier. A similar reaction occurs in the body after taking the vaccine. “Whether we have got the disease or not, if our antibody test is positive, then we get to know whether we have come in contact with the virus or not. Our body produces antibodies in response to exposure to the virus,” said Dr Shahid Jameel.

Is it necessary to have antibodies after taking the vaccine?

Antibodies are usually prepared in large quantities after taking the vaccine, and after taking the complete dose, you get protection from the disease. It is to be noted that these antibodies will protect against disease and not from infection. There is a misconception among people that after taking the vaccine, if specific amount of antibodies are not produced, then they’ll not be protected from the infection. Dr Jameel says, it’s rare for antibodies to not be formed after vaccination, but it’s known to happen and can be attributed to some genetic abnormalities. In an earlier story on FIT , we had explained that there is a threshold of an antibody test.

Does a higher count indicate more protection?

Dr Jameel says that whether the count is 100 or 1,000, the vaccine provides equal protection. However, according to the science of vaccinology, for the best response, we should take the booster dose or the second dose of the vaccine when the antibody level comes close to the baseline. “For the best immune response, it is advised to allow the antibody to drop after reaching the threshold level 10. The second booster dose is then most effective. Although this applies equally to all people, it is not necessary. Antibody tests are mostly performed commercially in large pathology labs. But in the private domain, its cost is almost double the cost of the vaccine,” he adds. However, Dr Jameel also says that it is not feasible for common people to have their antibody level checked repeatedly after infection, or after taking the first dose of the vaccine and wait for the antibody levels to drop, before deciding to take the second dose. This cannot be recommended at population level.

Can an antibody test indicate the efficacy of a vaccine?

No, vaccine efficacy can only be tested in a proper placebo-controlled clinical trial. No antibody test can measure vaccine efficacy.

What’s the difference between a sero survey and an antibody test?

Dr Jameel explains, “For example, we conduct a sero survey in some area and we find that antibodies were found in 57 percent of the population there. This does not mean that 57 percent of the people have had the disease, some may have only been exposed to the virus.” Antibody test, on the other hand, consists of qualitative and quantitative tests. The qualitative result indicates whether there has been an exposure to the virus or not. A quantitative test, which is called an ELISA test, tells us if we have developed antibodies and to what extent.

Confused with all this information? Don’t be.

Dr Jameel explains, “Viruses have two different types of proteins – spike protein (S Protein) and nucleocapsid protein (N Protein). The S protein is on the surface of the virus and the N protein is found inside the virus. Most vaccines against coronaviruses are based on the S protein. Covishield, the vaccine used in India, is based on the S protein and this vaccine will produce S antibodies. Covaxin, on the other hand, is a whole virus vaccine, so it will produce both S and N antibodies.” But this does not mean that a vaccine that produces both S and N antibodies will offer more protection.

ADVERTISEMENTREMOVE AD

Members Only

FAQ: Should You Get an Antibody Test After COVID Vaccination?

What will this test tell you? How will it help? Here’s all you need to know.

Kaushiky Kashyap

Published: 01 Apr 2021, 11:41 AM IST

F.A.Q

Small

Medium

Large

An essential tool to prevent the spread of coronavirus is to 'test, test, test.'

According to experts, it's essential to test extensively to understand the spread of the disease among the population. New variants of SARS-CoV-2 and COVID-19 vaccines have increased the curiosity around testing for antibodies.

This curiosity around whether we already have COVID-19 antibodies, or to know if the the vaccine is effective, has led to an increase in antibody testing. In some cases, elderly patients are being advised to test for antibodies by doctors before taking the second dose.

BECOME A MEMBER

FAQ: Should You Get an Antibody Test After COVID Vaccination?

What will this test tell you? How will it help? Here’s all you need to know.

Read Latest News and Breaking News at The Quint, browse for more from coronavirus and faq

Topics: COVID-19 FAQ coronavirus FAQ