Coronavirus antibody tests are being touted as a potential way to relax social distancing measures. Certainly, reliable tests could help understand which groups of people have been previously infected with SARS-CoV-2 and how to stop further spread of COVID-19. But experts say the promises of currently available antibody tests for coronavirus may be overhyped.
When a person is infected with a virus, their immune system produces antibodies to fight off the unwanted invader. In theory, those antibodies should later infer some level of immunity. While there is no reason to believe this won’t be the case with the new coronavirus, the World Health Organization (WHO) warned at a press conference last Friday (April 17) that coronavirus antibodies don’t necessarily guarantee long-term COVID-19 immunity for recovered patients or former asymptomatic carriers.
So far, three types of SARS-CoV-2-specific antibody have been detected in patients who have recovered from COVID-19. But many questions remain surrounding both the accuracy of these rapidly developed SARS-CoV-2 antibody tests and their reliability, as research labs and biotech companies around the world clamour to develop antibody tests and governments stockpile kits.
Germany has begun Europe’s first large-scale coronavirus testing to monitor the spread of the virus and infection rate. Boris Johnson has referred to coronavirus antibodies as a potential ‘game-changer’. In the US, the Food and Drug Administration (FDA) is allowing the use of antibody tests that have not been reviewed yet to diagnose active COVID-19 infections. And similar approaches are being taken in other countries like Australia.
In times like these, experts say such emergency measures are appropriate. Even so, scientists point out many challenges to overcome before the tests will be as useful as hoped.
First of all, antibodies take time to appear. So, if someone has symptoms for one week, it is unlikely they will have the antibodies. But the idea is that once these antibodies are present, that person will be immune to future infections. However, since the tests don’t detect the virus itself, they are not as useful as a diagnostic tool. Antibodies in the blood simply indicate that someone had the virus in the past.
In addition, commercial antibody kits typically undergo rigorous trials on hundreds of people to verify their accuracy. In view of the current pandemic, governing bodies have relaxed the rules and given the green light to laboratories and health-care workers to use, which means the tests available right now have not been fully vetted as yet.
Another problem is if the test is performed too early, the body will not have time to develop the antibodies. This could easily result in missed infections. False positives are another worry since the body might produce the same antibody against other viruses. Furthermore, as mentioned above, testing positive for SARS-CoV-2 antibodies does not necessarily guarantee immunity to the virus.
Immunity is inferred by neutralizing antibodies, which prevents the virus from entering cells. As yet, scientists don’t know whether all recovered COVID-19 patients develop these antibodies (1). And the tests also can’t confirm that the previously infectious person is no longer infectious. Indeed, they may still be shedding the virus. Even so, many politicians are pushing the idea of an ‘immunity passport’.
There is little doubt that reliable antibody tests will provide an important piece of the SARS-CoV-2 puzzle. One day, they may even be used to diagnose infections missed by standard PCR tests. But as with any new technology, more time is required to iron out the kinks, thus, early results should be approached with caution.
(1) Wölfel, R. et al. Virological assessment of hospitalized patients with COVID-2019. Nature (2020). DOI: 10.1038/s41586-020-2196-x