A group of doctors has questioned how “game changing” coronavirus antibody tests really are.
Boris Johnson praised their potential early in the outbreak, with the government later buying 10 million of the kits when Public Health England (PHE) studies suggested their effectiveness.
On 21 May, health secretary Matt Hancock called a reliable antibody test an “important milestone” that would safely free survivors of the infection from the confines of social distancing.
A month later, Baroness Dido Harding – who heads the NHS test and trace programme – stressed it is unclear to what extent antibodies protect against a second coronavirus infection.
This sentiment – and other concerns – has been echoed by the group of senior medics, with one stressing “we don’t have much data and we can’t trust any of it”.
Antibodies ‘do not guarantee immunity’
Antibodies are immune-fighting proteins released when the immune system picks up on an infection.
Once the infection has passed, memory antibodies circulate at low levels in the blood.
If the infection is identified again, the immune system ramps up production of these proteins, preventing the virus from taking hold.
Testing positive for coronavirus-specific antibodies suggests an individual has some protection against the infection, however, no one can say for sure this is the case or how long it lasts.
After reviewing the studies carried out to date, Professor Jon Deeks from the University of Birmingham concluded “we don’t have much data and we can’t trust any of it”.
Antibodies do “not guarantee immunity” against hepatitis C, flu or the virus responsible for bronchiolitis – inflammation and congestion of the small airways.
“What people really want to know from these tests is, ‘am I safe from infection?’,” said Dr Al Edwards from Reading University. “These tests, at the moment, can’t answer that.”
Assuming coronavirus antibodies do ward off a second infection, how long that lasts is unclear.
A measles vaccine offers lifelong protection, while the most effective jab against cholera leads to antibodies being produced for just five years, hence the need for boosters.
The coronavirus is one of seven strains of a class of viruses that are known to infect humans.
Others include Severe acute respiratory syndrome (Sars) and Middle East respiratory syndrome (Mers), which killed 774 and 858 people in their 2002/3 and 2012 outbreaks, respectively.
“People who were infected with Sars and Mers produced antibodies against these illnesses following infection, for up to three years in some cases”, said Dr Tom Wingfield from the Liverpool School of Tropical Medicine.
“However, it is not clear whether the presence of these antibodies means that a person is immune to a repeat infection”.
No confirmed cases of Sars have been reported since 2004, while only a handful of Mers incidences arise every year.
A gap in expert knowledge over coronavirus antibodies has caused many to dismiss “immunity passports”, an idea that was floated early on.
Dr Andrew Preston from the University of Bath called them “attractive but some way off”.
Nevertheless, NHS England and NHS Improvement wrote to trusts on 25 May asking them to “offer antibody testing at short notice and ramp up capacity to thousands of samples a day”.
“I share the concerns that antibody testing is being rolled out before we fully understand the immune response to [the coronavirus], what the results of these tests may mean and what actions to take based on test results”, added Dr Wingfield.
“Another critical unknown is what advice to give someone who has a positive or negative antibody test and how the result and such advice might influence their behaviours, including social distancing, and thereby impact upon [the coronavirus’] transmission”.
Accuracy of tests questioned
Putting uncertainties about the extent of coronavirus immunity aside, other concerns linger.
The government bought its kits from the pharmaceutical giants Abbott and Roche.
According to Professor Sheila Bird from The University of Edinburgh, there are several problems with PHE’s evaluation of these tests. These include the quality of samples, the absence of specific data according to age and sex, and the use of repeat samples.
The group of experts wrote in the BMJ: “Currently, there are no openly available data to compare the performance of these platforms.”
A PHE spokesperson said: “Our evaluations have been completed in record time using the samples and tests that were available to us.
“We are confident that the volume of samples and methodology was of a high standard.”
Abbott and Roche tests boast 99% and 100% specificity, respectively. A high specificity suggests if an individual has not been infected, the kit should not incorrectly pick up on antibodies, known as a false-positive.
Writing in a feature for The BMJ, journalist Stephen Armstrong said: “These figures came from the companies themselves and were based on those initial PHE studies and their own marketing material rather than peer reviewed research.”
Roche’s marketing material claims its test has a sensitivity – ability to correctly pick up on antibodies – of 100% 14 days after a patient was confirmed to have the coronavirus.
Abbott claims the same accuracy at 17 days after symptom onset. The PHE studies evaluating the kits also used date of symptom onset.
“The discrepancy between the times used makes it difficult to compare the two test kits, yet alone standardise them for use by the NHS,” wrote Armstrong.
A Cochrane review, considered the gold-standard of research, revealed none of the 54 studies that evaluated the tests’ validity fit the standards for reporting diagnostic accuracy, added Professor Deeks.
Government spent £16 million on inaccurate tests that ‘lie in storage’
The group of experts also stressed routine testing of patients is neither clinically urgent nor a clear public health need.
It takes time away from laboratory staff, as well as “hard pressed general practitioners being expected to provide patient counselling” around the results, they wrote.
“This push to introduce a non-evidence based test for uncertain gains risks inefficient use of scarce resources,” added the experts.
“We would like to see a carefully developed and clearly articulated strategy for serological testing, with clear scientific or clinical aims (or both) as part of a unified COVID-19 response strategy.”
COVID-19 is the respiratory disease that can be triggered by the coronavirus.
The financial consequences of all this antibody testing may also be vast.
“The UK government has already spent £16 million ($19.9 million) buying antibody tests from China that proved inaccurate, many of which now lie in storage,” wrote Armstrong.
“When it ordered 10 million of the Roche and Abbott tests, financial details of the deal were not disclosed.
“If the Abbott test is supplied at cost, however, there is evidence to indicate that the NHS will spend £79 ($98) per test.”
In a statement to The BMJ, 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.”
Nevertheless, it added antibody testing “will play an increasingly important role as we move into the next phase of our response to this pandemic.”
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