Does a Negative Antibody Test Mean the Vaccine Isn’t Working?

3 min read
Hindi Female

It has been claimed by some news reports that a screening test conducted by King George Medical College (KGMU), Lucknow revealed that 7 percent of the tested healthcare workers did not produce antibodies in spite of being fully vaccinated.

To get to the bottom of this, FIT spoke to Dr Tulika Chandra, Head of Blood and Transfusion Department at KGMU.

Dr Chandra explains that such a study is indeed being conducted by the Blood and Transfusion Department. The study target has been set on 4000 healthcare workers of KGMU. However, at present, 1000 people have been tested.

She clarifies the results of the study.

"90% of healthcare workers have developed antibodies, so we can easily move towards herd immunity if everyone is vaccinated. Many people who were not infected with COVID and just got vaccinated showed a high percentage of antibodies which is a good sign."
Dr Tulika Chandra, Head of Blood and Transfusion Department at KGMU.

She further explains that the lack of antibodies in 10% cannot be considered a sign of concern, because there are different reasons behind it. In fact, they are fairly encouraging.


The vaccine efficacy in India ranges from 70% to 80%. The results of the KGMU study are better as about 90% of the health workers have antibodies. The doctor says that if vaccination is done in the entire population, then the chain of corona infection can be broken.

Dr Chandra breaks down the data, explaining,

"In the negative antibody sample, 14 (1.4%) people had taken a single dose of the vaccine. 61 (6.1%) people had taken both doses. And 25 (2.5%) people were not yet vaccinated. Whereas, 9. (0.9%) were those who had tested positive for COVID in the last 4 months and 11 (1.1%) were those who were COVID positive before 4 months."
Dr Tulika Chandra

"These are initial observations. After completing the sample size, the detail analysis will be done," she adds.

What do antibody tests tell us about COVID vaccine efficacy?

COVID Vaccines and Antibody Production

First, a quick run down of how antibodies work and what COVID vaccines have to do with them.

Neutralising antibodies are produces by the B cells in the bone marrow in response to a pathogen (or a pathogen simulating vaccine) to defend the body against the intruder by neutralising or destroying them.

Vaccines work by triggering the body's immune response into producing specific antibodies to fight of a specific pathogen, and observing the amount of antibodies produced by the person post vaccination can be a helpful indicator of the effectiveness of the vaccine.

In a previous story on FIT, we’d explained that there is a threshold of an antibody test.

“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.”
Dr Shahid Jameel, Virologist

The average count comes from 300 to 1000 after the second shot of the vaccine.

But is testing antibodies an accurate assessment of the vaccine's effectiveness?

Speaking to FIT for another story, Dr Shahid Jameel explained that although 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.

“Vaccine efficiencies can be tested only during trial and compared with placebo. Antibody test cannot measure efficiencies.”
Dr Shahid Jameel

Dr VK Paul, chairman of the Central Government's COVID-19 Task Force and member of NITI Aayog, had also clarified this in a statement, saying,

“Antibodies alone do not indicate immunity of a person. Because when we take the vaccine If there are some changes in T-cells or memory cells, they become stronger and increase the resistance power. And T-cells are not detected by antibody tests because they are found in bone marrow.”
Dr V. K. Paul, Member (Health), NITI Aayog

According to Dr Jameel, the sensitivity and specificity (markers to indicate the accuracy of the test in detecting positive and negative cases) can also depend on a number of other factors such as the testing kit, the type of antibody test, and how many days after vaccination it is done.

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