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Monday, September 27, 2021

How to read spike antibody test

They show that our bodies can provide a good immune response after vaccination. But they should not be read as indicators of vaccine efficiency


August 22, 2021 7:36:55 pm
The Quantitative Spike Antibody test came to the front line when vaccine manufacturers across the world used it to monitor the response to vaccines. (Express File Photo By Amit Mehra)

Written by Alap Christy

“Me and my wife got a spike antibody test done a month after taking the second dose of the Covid vaccine,” said one patient. “My wife’s antibody titres were way higher than mine. Does this mean that she has better protective immunity than me?”, he asked. I am sure this question has baffled many of us after getting these tests. The CDC and ICMR have not recommended these tests for monitoring vaccine efficacy. What is the reason behind it gaining popularity day by day?

The pandemic has been hard on us. India has just recovered from the second deadly wave of infection. More than 4 lakh people have died due to Covid. Vaccines are the most effective tool for the control of infections. India commenced the vaccination programme in January 2021 and more than 58 crore shots have been administered so far. While avenues for new vaccines are opening, there is no clear data on vaccine efficacy.

The Quantitative Spike Antibody test came to the front line when vaccine manufacturers across the world used it to monitor the response to vaccines. It has attracted a good response, after being introduced in the market. However, there are questions on interpreting these tests, as raised by my patient, well since no one knows whether the levels of antibodies reported are protective enough? Also, some vaccinated people with spike antibody tests contracted Covid. Do we then question the efficacy of both the vaccine and the test?

We, at Metropolis, did a study on spike antibody titres in a population of 1,000 individuals grouped by their vaccination status. The vaccinated were further classified by the vaccine they took, its dose and history of infection pre/post-vaccination. Of those who took Covaxin, 84 per cent showed positive spike antibody titres compared to 97 people of Covishield. Those who were administered Covaxin had a lesser number of infections post vaccination – but the margin was statistically insignificant. Breakthrough infection cases were 23 per cent post the first dose compared to 0.96% of post the second dose, showing that two jabs have better protection. In contrast, levels of spike antibody with the first dose were much higher in people who were previously infected and none of them got a breakthrough infection.

Titres of spike antibody were five to six fold higher with Covishield when compared to Covaxin in people who had contracted Covid before. The comparative levels were two times higher in those without any known history of Covid infection. The probable explanation for this is the structure of the vaccine: Covishield is targeted specifically against spike protein, while Covaxin uses whole dead virus, there has the potential to target different parts of the virus.

While there is much discussion going on for the gap between two doses, we did not find any significant difference when we studied the spike antibody levels in different dose gap groups of Covishield. The Spike antibody levels in non-vaccinated individuals who were previously infected remained higher till six months compared to the ones who were infected before six months or more. Spike antibody titres can, therefore, provide remarkable information on immunity patterns in the Indian population. But they should not be used as a measure of vaccine efficiency – that’s a completely different ball game.

Covid immune response is a complex phenomenon that also involves T-cell mediated immunity. What we have now is something that can assess one part of the immune response against vaccines. It is not too much to say that in countries like India who are in a race to vaccinate large numbers of people, such a test has an important role.

I told my patient: Sir, while your immune response is lower than your wife’s, it does not say you have a higher chance of catching infection than your wife. Higher titres also indicate previous infection or probably a better humoral immunity, but your cell-mediated immunity may still be able to keep you protected. Regardless, do not lower your guard down. While our enemy has understood us well and has started changing its genome, we have a long mile to walk before we conquer it.

Why did I take the test then? asked my patient. Well, God forbid, if you get infected again, it is now sure that your body is capable of producing a good immune response. Wouldn’t that make us look at things more positively, especially when lockdowns are easing and we do not know where and when one can be exposed again? What about my nephew then – he has not developed titres even after the second dose? He asked me back. His humoral component has not shown positive results and there are chances his immune system is not responding to the specific vaccine. We will know more when we have more information on vaccines for non- responders. As of now, he has helped science and the country to evaluate the epidemiology of immune response and given motivation to vaccine manufacturers to improve their vaccine. Thank you; my patient said.

The writer, a physician, is Scientific Business Head – Clinical Chemistry, Metropolis Healthcare Ltd.

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