With the vaccination drives carried out in full swing, there are several questions and apprehensions about the efficacy of the vaccine and how it fights the virus. Thus, several people are resorting to taking Antibody tests, or in some cases, elderly patients are being advised to take the test by doctors before taking the second dose.
Thus, in an interview with the FIT, Dr. Shahid Jameel, virologist, and director, Trivedi School of Biosciences, Ashoka University talks about whether you need an antibody test after your vaccination is done.
How Does An Antibody Test Work?
An antibody test or serological (serum related) tests are done with the help of a blood sample. When infected, antibodies are produced by the immune system to neutralize the virus in the body. Even after the eradication of the virus, these continue to persist in the body for some time helping doctors to identify whether the patient was infected earlier.
Thus, a similar reaction occurs after the inoculation of the vaccine.
Dr. Jameel says, “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.”
Is It Necessary To Have Antibodies After Taking The Vaccine?
After taking the vaccine, antibodies are usually generated in large quantities and after taking a complete dose, you get protection from the disease. However, it is important that these antibodies protect from the disease and not the infection.
People have a misconception that after taking the vaccine, if a specific amount of antibodies are not produced, then they will lack protection from the virus. 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.
FIT reported, “Antibodies in the blood are measured in the International Unit (IU). Its range is from 0 to 1000. Usually, 10 IU per ml is considered a cut-off. Levels between 10 and 1000 are considered protective. However, it may not always be correlated. People with a count below 10 can also avoid the disease through cell immunity which is not measured by an antibody test.”
After the second shot of the vaccine, the average count comes from 300 to 1000.
Does A Higher Count Indicate More Protection?
According to Dr. Jameel, even if the count is 100 or 1000, the vaccine provides equal protection. However, the science vaccinology in order to achieve the best response, one should intake the second dose or the booster dose after 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 further feels that it is not possible for common people at the current population level to wait for their antibody levels to drop after taking the first dose of the vaccine or repeatedly check their antibody level checked after an infection.
Can An Antibody Test Indicate The Efficacy Of A Vaccine?
No, an antibody test cannot measure vaccine efficacy. Thus, vaccine efficacy can only be tested in a proper placebo-controlled clinical trial.
What’s The Difference Between A Serosurvey And An Antibody Test?
Dr. Jameel states, “For example, we conduct a serosurvey in some area and we find that antibodies were found in 57% of the population there. This does not mean that 57% of the people have had the disease, some may have only been exposed to the virus."
However, on the other hand, an Antibody test comprises qualitative and quantitative tests. The qualitative test result denotes whether there has been a virus exposure or not. A quantitative test, which is called an ELISA test, given an account of whether one has developed antibodies or not, and up to what extent.
Here Is A Brief Explainer
Dr. Jameel explains, “Viruses have 2 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,” he adds.
However, this does not imply that a vaccine that produces both S and N antibodies will offer more protection against the virus. This is because antibodies work towards neutralizing the virus by binding to the surface of the virus. With the N protein not present on the surface of the virus, it will not be able to neutralize it.
The S antibody contains parts that work as neutralizing antibodies to prevent the virus from binding to the cell. Suppose you have 100 molecules of S antibody in the body, then there will be 10 neutralizing antibodies in them.
Thus, an antibody count should not influence the decision to get vaccinated, as amidst the high surge in COVID cases, vaccination is the need of the hour to protect the elderly and the people most vulnerable to the virus.