Antibody tests have no practical use, claim experts
THE rapid roll-out of coronavirus antibody tests risks giving people false hope of immunity based on “untrustworthy” data, senior scientists including a World Health Organisation adviser have warned.
Writing in the BMJ, the experts say the NHS risks wasting valuable time and cash focusing on tests that, so far, serve little clinical purpose.
Last month, Public Health England announced that it had validated two laboratory-based blood tests, made by Roche and Abbott, which indicate whether a person has previously been infected with Covid-19 by detecting antibodies. Boris Johnson had previously described this capability as “game changing”.
About 35,000 such tests are now carried out each day. However, the experts in the article say that because it is not yet known whether antibodies confer immunity from reinfection, a positive antibody test currently has no practical significance, even for healthcare workers.
“Those with a positive test should still consider themselves at risk and fol- low infection control policies designed to prevent nosocomial [in-hospital] spread and the risk of infection,” they write.
“There is, therefore, no benefit to the healthcare organisations or to others in knowing the status of employees at present.”
Published papers from the Government’s Scientific Advisory Group for Emergencies (Sage) have revealed members’ concern about the misuse of positive antibody test results, and any notion of “immunity passports”.
These include worries that employers might discriminate against people without a positive test result when allocating work, possibly leading to a black market in positive certificates or even people choosing to deliberately get infected.
Most scientists agree that antibodies will confer some immunity for at least a handful of months. Research into other types of coronavirus shows that immunity wanes within or shortly after one year.
The experts also question the companies’ claims of accuracy, complaining of limitations in the information they have published.
Prof Jon Deeks, who advises the WHO and led the first systematic review of the studies supporting the antibody tests, said: “We don’t have much data and we can’t trust any of it.”
Roche, whose test was the first to be validated, initially boasted that it had 100 per cent sensitivity (the ability to correctly identify positive samples) and more than 99.8 per cent specificity (the ability to correctly identify negative samples).
Data later released from PHE’S evaluation showed that although 100 per cent of samples taken from individuals who had not had Covid-19 accurately came back as negative, 16 per cent of samples taken from people who had been infected did not show as positive.
The BMJ article also calls for detail on the accuracy of the tests to be categorised by age group and racial grouping.
“Those who are at highest risk of death from this infection are elderly people, those from black and minority ethnic groups and immunocompromised people,” it says.
“There are currently no data showing the performance of the tests in these groups.”
The Department of Health and Social Care said: “We do not currently know how long an antibody response to the virus lasts, nor whether having antibodies means a person cannot transmit it to others.”
But it reiterated that antibody testing “will play an increasingly important role as we move into the next phase of our response”.
PHE said its evaluations had “been completed in record time using the samples and tests that were available to us”. It added: “We are confident that the volume of samples and the methodology was of a high standard.”
A spokesman for Roche Diagnostics UK said: “We are rolling out antibody tests to the NHS as part of the crucial next step in understanding the spread of this virus, and providing greater confidence and reassurance as we move into the next phase of our response to this pandemic.”
16pc
The percentage of people who had been infected that did not show up in Public Health England’s evaluation of the tests