Antibody tests are here, but government is on course for another testing fiasco | thearticle

The Covid-19 antibody test developed by Roche, the Swiss pharmaceutical giant, has been approved for use by the NHS. It’s welcome news. In the absence of concrete knowledge about what a

positive result means, the government needs a clear strategy on its use to avert a second, potentially more deadly wave of testing chaos. Edward Argar, the Health Minister, immediately used

the announcement to stress that the first people to be tested will be frontline NHS staff. Argar’s suggestion that this was a “game changer” is a potentially dangerous remark for a

government minister to make — we still do not know what significance there is to having caught Covid-19 and subsequently producing antibodies. What he seems to have been suggesting is that

an antibody test will give NHS staff the “all clear” to return to work, on the assumption that they have produced some degree of immunity. This is a step far beyond current scientific

knowledge and any suggestion that this is a magic bullet to lift lockdown is irresponsible. Unsurprisingly the wave of wildly speculative headlines about holidays resuming and so-called

immunity passports immediately followed. As the Prime Minister made clear in his address to the nation on Sunday night, the future is unclear. While we hope for a vaccine, we cannot plan for

the future on the assumption that one will ever be developed. Similar logic should be applied to antibody testing if the government is to avoid yet another fiasco. In the absence of

concrete knowledge about immunity, the government should not predicate its testing strategy on presumed validity. Doing so would set a dangerous precedence for the general public, who either

know or assume they have had Covid-19 and might then assume they are immune. Although a recent Chinese study suggests that 95 per cent of patients who have Covid-19 develop antibodies, the

reality is that we do not know if any or indeed partial, temporary immunity is conferred or for how long this might last. Nor do we know if people with antibodies might nonetheless still

carry and transmit Covid-19. In the absence of such knowledge, antibody testing should be rolled out on a strategy for establishing prevalence of the disease in the general population,

knowledge that is of epidemiological significance. The test comes less than 24 hours after a paper in the journal _Science_ by the Pasteur Institute estimated that no more than five per cent

of the population of France and Spain had contracted Covid-19, far less than might suggest a move towards “herd immunity”. The problem is that these estimates are based on modelling. A

properly targeted antibody test will produce far more accurate sampling and in so doing boost significant areas of knowledge about the disease, such as its mortality rate. The new Roche test

is laboratory based, rather than the point of care test the government seemed poised to roll out in April and this will slow down its application to the general population. As TheArticle

reported last month, the PCR test used for diagnosing people who currently have Covid-19 has a significant problem with false negative results. This conclusion was confirmed by a paper in

the _British Medical Journal_ two days ago. That paper recommends that doctors do not use a single negative PCR test result to rule out Covid-19 in patients with symptoms. Although the new

Roche antibody test measures whether you have had the disease rather than currently have it, thankfully it is considerably more sensitive and specific than the PCR test. The Roche test has

99.8 per cent specificity and sensitivity of 100 per cent — in other words it has no chance of telling people they have antibodies when they do not. As Jeremy Hunt put it recently, it is

“pretty clear now” that community testing should not have been abandoned on March 12. This is not really a clinical issue — the PCR test was and remains too unreliable as a diagnostic gold

standard, but community testing is epidemiologically significant in measuring the prevalence of the disease. Without this knowledge we cannot possibly hope to escape lockdown or make

informed public health decisions as we adapt to living with Covid-19. Let us hope that the government has learnt from its own mistakes and rapidly produces a coherent strategy for antibody

testing that causes no further harm.