As the world is increasingly looking at ways to ease the coronavirus lockdown, immunity tests are gaining more and more attention. The idea of such a test is that it would detect not who has the disease now, but who has had it in the past and has developed an immune response. In other words, it would detect who is immune to the disease and can safely reemerge into society.
The only problem is, these tests might not work well enough.
"There is an urgent need for robust antibody detection approaches to support diagnostics, vaccine development, safe individual release from quarantine and population lock-down exit strategies," the authors of a new study write.
The researchers were led by Professor Derrick Crook of Oxford University in the UK. The UK has had its own unfortunate experience with immunity tests, having purchased millions of such tests from China, only to find out that they didn't work.
The UK's bad tests might not be an exception. Several antibody tests have been questioned by scientists and for all their promise, the results of antibody tests have been surprisingly uncertain.
So Crook and colleagues analyzed 142 blood samples from adults (from ethically approved sources). They used nine different commercially available tests, although they did not disclose exactly what the tests were.
The results, however, were clear: the commercial antibody tests -- also called lateral flow immunoassay (LFIA) devices -- are not sensitive enough. None of the nine tests were accurate in all instances, all had shortcomings, particularly when it came to detecting samples without the antibodies.
So where does this leave us? Well, the Oxford researchers didn't analyze all of the available antibody tests, so there may still be others that are effective. The published result is also a white paper, not a peer-reviewed paper, so other experts haven't had their say on the Oxford results.
Expert reactions have been mixed regarding the study. Richard Tedder, visiting professor in medical virology at Imperial College London, said there is very little usefulness to this study.
“Interesting though the data are, they are simply of no value at this time as there is no way of relating the Oxford findings of an in-house assay to those PoCT assays which are currently known about in this country.”
Meanwhile, Eleanor Riley, professor of immunology and infectious disease at the University of Edinburgh praised the paper and said it highlights the need for more accurate tests. She also added that even with the shortcomings, existing tests might be useful.
“It shows that the problem with the commercial rapid antibody tests is that they are not sensitive enough – they fail to pick up antibodies in over a third of people who do in fact have antibodies."
"However, these tests do have acceptable levels of specificity – that is, they are only picking up people who have genuinely been exposed to the Covid-19 virus."
"This means if your test is positive, you can be confident that you have been infected and have antibodies. But if your test is negative, you can’t rule out that you might have been infected."
Nevertheless, this is a strong indication that we might not be as close to accurate immunity tests as we thought -- but this doesn't mean that they're any less significant.
The study concludes:
"LFIA devices are cheap to manufacture, store and distribute, and could be used as a point-ofcare test by healthcare practitioners or individuals at home, offering an appealing approach to diagnostics and evaluating individual and population-level exposure. A positive antibody test is currently regarded as a probable surrogate for immunity to reinfection. Secure confirmation of antibody status would therefore reduce anxiety, provide confidence to allow individuals to relax social distancing measures, and guide policy-makers in the staged release of population lock-down, potentially in tandem with digital approaches to contact tracing."
The study has been published in the pre-print platform medRxiv.
