advertisement

Infectious Diseases

Updated 15 June 2020

Covid-19 antibody tests: Will they be reliable enough to manage the pandemic in the future?

SARS-CoV-2 produces antibodies in the blood after a person has had the virus, but does this mean you are immune if an antibody test is positive?

  • There are currently two approved antibody tests for SARS-CoV-2.
  • These antibody tests can indicate if you've had Covid-19.
  • Experts are still unsure if this could determine immunity.

Countries around the world are slowly lifting hard lockdown restrictions to allow businesses and institutions to open safely without spurring another more severe wave of infections.

Many researchers agree that part of managing the pandemic involves determining who has already been exposed to SARS-CoV-2 and built up antibodies.

The method to do this? A reliable, accurate, readily-available antibody test.

There are, however, still a number of questions to be answered about whether an antibody test is possible and whether it will work.

What is an antibody test and what makes it different from the tests we already have?

An antibody test is not used as a diagnostic tool like the RT-PCR test and should not be used on a person who is showing symptoms.

The RT-PCR test is done when you are suspected of having contracted Covid-19. A swab is taken from the nasal passage or throat, and sent to a lab to check for viral material in the sample.

But the antibody test is different. This test looks for immunoglobin levels in the blood to tell whether you have had Covid-19 and built up antibodies.

Whenever your body is exposed to a pathogen such as a virus, the body's immune system responds by producing protective measures to help you fight infection.

This agent is described as a Y-shaped molecule that attaches itself to foreign proteins such as bacteria and viruses and destroys infected cells, explains Patricia Slev who runs ARUP Laboratories, affiliated with the University of Utah.

How exactly does this test work to detect the antibodies in the blood?

According to a paper published in Chemical & Engineering News, antibody tests vary from manufacturer to manufacturer, but they all fulfil the same basic task - to detect antibodies.

Tests involve a tube of human blood being centrifuged to separate plasma from red blood cells. There is also another tube with bits of viral protein.

When the blood in the first tube has antibodies, it will be able to recognise the viral matter in the other tube and they will stick to each other.

This result means that there are antibodies present in the blood and that the person has had Covid-19 and has built immunity.

What is the current problem with these tests?

According to Shobita Parthasarathy, a science and public policy expert at the University of Michigan, many view antibody tests as a quick solution to determine whether an individual can safely venture back into society and as a tool for institutions such as businesses and schools to determine when they can reopen.

But, as she told Chemical & Engineering News, this is a lot of pressure to place on one test, as the scale of tests needed and the scope of their use in public can be ethically and logistically messy.

Earlier during the outbreak, there were several reports that these antibody tests might not be accurate and reliable and went onto the market without any regulation or standardising.

For example, the UK government spent £16 million on millions of tests - and none of them met the accuracy requirements when tested in laboratories.

But, according to Alex Greninger, a virologist and diagnostics expert at the University of Washington, these tests are slowly getting better, especially after the FDA demanded that they be validated.

The only tests currently approved are the Roche and Abbot tests, which were found to give 100% accurate results in people who had been infected with SARS-CoV-2.

If you have antibodies, are you immune?

When the antibody test has a positive result, it means that SARS-CoV-2 antibodies have been found in your blood and that you have been infected by Covid-19.

However, this doesn't necessarily mean that you are completely immune to coronavirus, which defeats the purpose of using antibody tests as a proof of immunity to allow people back into society.

The truth is, scientists are not sure how much immunity you have after Covid-19 infection, even with the presence of antibodies.

Simply testing positive for antibodies doesn't mean you can slack off on physical distancing and hygiene measures.

Another thing that the SARS-CoV-2 antibody tests can't determine is how long these antibodies will last.

With some infections, the level of antibodies wears off over time, and that's why booster vaccines are needed to help your body produce these antibodies again.

As we are still in the process of developing a vaccine, scientists also can't tell whether these antibodies will last long enough.

But Greninger is positive that these antibodies can stick around for a long time, as early tests suggested that people with Covid-19 produce a large amount of antibodies and that the virus only mutates slowly.

How readily available will antibody tests be?

According to the paper in Chemical & Engineering News, Roche's tests will reach a maximum production of tens of millions of tests for the entire globe by June, and Abbott also indicated mass production of these tests.

Currently the situation and availability for antibody tests in South Africa is not determined. Parthasarathy told Chemical & Engineering News that there is still concern about availability in the US alone as the demand will simply skyrocket.

A way back to normality?

So, will antibody tests be sufficient to allow us back into society?

Even though Greniger is optimistic about the future of these tests, other experts are still wary about rushing back to into society, as this might trigger a second wave of infections, and that the antibody tests are not yet able to tell us enough about our risks of getting reinfected.

READ | South Africa's Covid-19 testing strategy needs urgent fixing: here's how to do it

READ | Scientists warn of false-negatives with Covid-19 virus tests – what are the SA implications?

READ| Covid-19: Behind SA's shortages of test material

Image credit: Pexels