The Health Secretary, Matt Hancock, says he wants to see 100,000 coronavirus tests per day by the end of this month.
New blood tests will form part of the testing drive. But these tests have already created confusion and controversy, with government officials at loggerheads with journalists over the science.
Here’s what we know and what we don’t know.
What are the different kinds of test?
The tests being used on many hospital patients and some NHS workers now are called polymerase chain reaction (PCR) tests.
They detect the presence of RNA – genetic material from the virus – which should tell us if someone is infected now.
But swabs must be taken from the patient’s nose or throat and sent away to labs for testing, which takes time.
And independent experts have told FactCheck that as many as 30 per cent of results could be false negatives, so many patients have to be tested more than once to get an accurate result.
The new test Mr Hancock wants to roll out alongside the swab test is done on samples of blood. He referred to it as “the blood test” but it is more commonly known as an antibody or serologic test.
This antibody test does not detect the presence of the coronavirus itself. It shows whether the immune system has created antibodies to fight it.
The government has previously said it has ordered millions of kits. They should be available for use soon but are apparently still being assessed by officials.
Why do we need a new kind of test?
The antibody test tells us whether someone has had coronavirus at some point in the past.
Amongst other things, this means that key workers who have been infected coronavirus – perhaps without experiencing symptoms – may be able to return to work without fear of catching it again.
In theory, if someone has the antibodies to fight a virus, they should be immune to it in the future – at least for a while – though scientists have yet to prove if and how this might work in the case of coronavirus.
Does the blood test show if you have coronavirus now?
This point proved hugely controversial this week when the Professor Jonathan Van-Tam, the Deputy Chief Medical Officer for England, appeared on ITV’s Peston show.
In a video clip which quickly went viral, Professor Jonathan Van-Tam told Robert Peston he had got the science wrong, saying: “The blood tests test whether you have had it. They cannot ascertain whether you have it at the moment.”
The journalist had said: “The point about these tests is they don’t just tell you whether you’ve got the kind of antibodies which give you immunity, but in theory they will also be able to speed up the testing very considerably of people who have actually got the virus.”
He went further in a blog on the Spectator website, writing that antibody tests “can be used to identify whether someone who has symptoms actually has the virus”.
“They would therefore be a cheap, efficient alternative to the laboratory tests that the government is struggling to scale up…”
Scientists and manufacturers contacted by FactCheck were clear that antibody tests alone cannot provide a complete alternative to the viral tests we are using now – they can only complement them.
This is because the body only produces antibodies several days after you catch the virus.
If you are given an antibody test in the first few days, the result might be negative even if you have the illness.
FactCheck spoke to Biopanda Reagents, a Belfast-based manufacturer and supplier of Covid-19 antibody testing kits.
The company has produced a graphic that shows how the testing process works. The first antibody, called IgM (the green line) is only detectable after several days of infection:
The immune system produces another antibody later (IgG – the red line) and this provides long-term immunity.
We can see from the graph that there is an initial period lasting several days when you might have the coronavirus, and may have already developed symptoms – this is the blue line – but you would not test positive for the IgM antibody.
Han Yan from Biopanda told us: “I have to stress that the timescale is presented only to give a very general idea of the dynamics of the humoral immune response, as every person’s immune response differs.
“As you can see, there is a window period where a person can be infected, and even show symptoms, but during which the antibody test will not come back positive. However, during this time, a PCR test should detect the presence of the virus.
“With all this in mind, we would never recommend our antibody test as a way of replacing RT-PCR for early-mid stage diagnosis of COVID-19 because of the risk of false negatives…
“So if the antibody test is being used to diagnose current infection, it must be used with RT-PCR, and with other clinical information such as scans of the lungs. It is best used to provide evidence of historic infection.
“If you want rapid diagnosis of current infection, you ultimately have to look for evidence of the virus itself, and not the body’s immune response.”
Why use both?
While antibody or “serologic” tests may not be the best choice for early diagnosis on their own, evidence from China suggests combining them with PCR testing can dramatically improve the chance of an accurate result.
A study of blood samples from 173 patients in Shenzhen found that an antibody test started to give more accurate results than a PCR test after the first five and half days of illness.
Combining the blood test with the PCR test enabled doctors to detect 98.6 per cent of coronavirus cases compared to 51.9 per cent with a single PCR test, according to a review in the New England Journal of Medicine.
The authors concluded: “Serologic tests can improve early diagnosis of Covid-19. Because of the high false-negative rates with PCR, serologic tests will be a useful supplement to RNA detection.”
So some scientists think it’s too simplistic to say that antibody tests cannot show current coronavirus infection.
Dr James Gill, a locum GP and Honorary Clinical Lecturer at Warwick Medical School, told FactCheck: “The best test for an early infection is combining the antibody test AND the PCR swab taken from the patient.”