Will the UK’s new COVID-19 tests work?

Testing is a crucial way in which governments can tackle the new coronavirus – SARS-CoV-2. Across the world, public health labs and private companies have been working flat out to provide new antibody tests and expand our capacity to test people for the virus itself.

There are some encouraging signs for the UK. During a press conference held on March 24, the Health Secretary Matt Hancock, who has now been tested positive himself, said that the government has bought 3.5 million antibody tests. However, we do not quite know if and when these will be made available.

And yesterday, at the latest Downing Street press conference, Michael Gove announced that the government – in alliance with businesses, research institutes, and universities – will be rolling out new viral antigen tests for frontline health and social care staff.

Another way of expanding virus testing capacity may also be close. This could be achieved by speeding up the processes involved in PCR tests, which can detect specific genetic material within the virus and determine whether a person is infected or not.

The German engineering company Bosch, in partnership with Randox Laboratories, a UK-based diagnostics firm, have apparently cracked this. Yesterday they unveiled a new rapid coronavirus test which, using a user-friendly remote device that can be used in hospitals to provide results in under 2.5 hours. The devices can perform up to ten tests in the space of 24 hours. That means 100 devices would be able to evaluate up to 1,000 tests per day.

At the same time, a partnership between the Mologic, a UK diagnostics developer, and a Senegalese Research institute is trialling a pocket-sized PCR test which will be able to give results in ten minutes.

This is very well, but will these new tests actually work?

There are potential pitfalls with any of these tests. No diagnostic system is perfect: they rely upon one sample taken at a particular point in time. They need to be developed, checked, and trialled carefully to ensure that they are accurate and will give reliable results.

Even then, there will be a margin for error. The key will be to minimise that margin. It cannot be eliminated entirely, but prematurely rushing out test kits will likely increase the chance that they are faulty.

The Spanish newspaper, El País, has reported that Spanish microbiology experts believe a series of rapid PCR tests produced by a Chinese company, Bioeasy, can only correctly identify positive cases 30% of the time. The standard requirement for an influenza test is 80%.

“False negatives”, when a test fails to pick up a person who is infected with the coronavirus, are a potential pitfall which can be mitigated by combining a test with CT scans and the assessment of symptoms.

With the antibody test, particular caution is needed. They rely upon antibodies targeting a cloned version of a protein found on the coat of SARS-CoV-2. There is a possibility that the diagnostic could pick up different types of antibodies which are used to targeting the same or similar proteins to that which are found on the coat of the novel coronavirus.

Here, “false positives” are the dilemma which need to be guarded against. If significant numbers of people are told that they have immunity when they do not, this would severely undermine attempts to fight the transmission of COVID-19.

Despite these potential pitfalls, industry groups and labs developing rapid tests and new immunoassay tests seem to be quietly confident.

Bosch and Randox claim that their new rapid PCR test has been accurate in 95% of its validation tests. And a Berlin-based company, Pharmact, has said that the antibody test it is developing has tested well, with “a true negative rate of 100%”, meaning “zero false positives”.

Pharmact’s medical directors hasten to add that the test is more effective during later stages of the infection than it is in the earlier stages. The test can pick up positive cases around 70% of the time when a person has been fighting off the virus for 4-10 days, but this rises to 98.6% by the 24^th day, which likely reflects the increase in antibodies over this period.

All of these considerations will have consequences for the UK’s public health authorities as they begin to assess whether or not the prototype antibody test they have will be able to be rolled out in large numbers.

Public Health England’s microbiology and public health expert, Professor Sharon Peacock, suggested to MPs this week that these tests could be bought by the general public online from Amazon and from pharmacies within days once they are approved by the authorities.

Chris Whitty and Sir Patrick Vallance have since attempted to temper expectations at a Downing Street Press Conference this week. They pointed out that establishing the accuracy of the purchased antibody tests is a priority.

“That is so important that if it means a delay to get there, that delay is worth having”, Vallance said. He added that: “We must make sure that we get the quality of this absolutely right.”

Once the tests are produced, they can be rapidly scaled up using factories and facilities that are used to producing similar tests in large quantities. But this will still take time, and supplies of particular resources required in making new antibody tests – such as reagents – will also need to be secured.

With the UK’s frontline NHS staff likely to be the target of the first antibody tests which become available, it seems doubtful that such test will be accessible to all from Amazon and Boots right away. But we might expect this to happen once the UK’s authorities are confident in their ability produce an accurate antibody test that can be scaled up while maintaining the crucial element of quality control.