What is Novel coronavirus (2019-nCoV)?
Video / WHO
By Henry Bodkin,
As the downhill lines on the Downing St graphs each evening attest, Britain's lockdown has successfully pushed the Covid-19 reproduction rate to below 1.
In Boris Johnson's words, "We have begun together to wrestle it to the floor." But as the economy gasps for air and publiccompliance with the lockdown frays, Government scientists are trying to work out if we could keep the virus at bay with less draconian measures.
However, on three questions crucial for an exit strategy, the evidence is anything but clear.
Arguably the most pressing unknown is whether we really need to stay two metres apart to suppress transmission. The fact that the UK Government's recommended separation of two metres is double that of the WHO has attracted criticism.
The UK guidance is based on research from the 1930s that concluded droplets in coughs or sneezes tended to evaporate or fall to the ground within two metres.
Senior ministers are known to be unhappy with the quality of the evidence and have instructed scientists on the Scientific Advisory Group for Emergencies (Sage) to review it. Their scepticism echoes that of many experts.
However, a different body of evidence indicates that the virus can travel longer distances on tiny, lighter particles called aerosols.
One Chinese study of intensive care units concluded four metres was safer. Meanwhile a review in the New England Journal of Medicine suggested Covid-19 can float in the air for three hours and remain infectious.
Sage is expected to publish a paper this week addressing the risks of catching Covid-19. Whatever its conclusion, it is almost certain to stress that handwashing remains the most effective measure of suppression.
Herd immunity
To navigate a safe passage out of lockdown, officials ideally need to know how many people have had the virus. This, they hope, will allow them to estimate the proportion of the population that is still vulnerable, its distribution, and therefore the dangers of a second spike. This is an incredibly difficult figure to arrive at, as yesterday's rival "Independent Sage" meeting showed.
Professor Karl Friston pointed to Californian data that suggested up to 50 per cent of people had caught the virus, many with no symptoms. He said such levels of "herd immunity" would preclude a second flare-up.
He was immediately contradicted, by other leading scientists who pointed to data from New York, which has been far harder hit, suggesting only 25 per cent had been infected. To clear up the uncertainty, officials are pinning their hopes on an antibody test that looks for past evidence of an immune response to the infection.
Ministers got badly burnt earlier in the crisis by promising an easy-to-use home test "within weeks", only to find that no reliable technology existed. Optimism has increased in recent days after the US approved an antibody test from Roche Diagnostics that boasts 99.8 per cent accuracy, which Public Health England is also understood to be considering.
Professor John Newton, Britain's national testing co-ordinator, said this week he was confident tests would come online this month. This begs two questions.
Firstly, whether those infected carry enough antibodies for a test to detect.
Last month, Chinese researchers analysed blood from 175 discharged patients and found nearly a third had surprisingly few antibodies. However, Professor Jonathan Van Tam, the UK's deputy Chief Medical Officer, told a Downing St press conference that the "overwhelming" majority of Covid-19 patients who had donated blood to an NHS trial over recent weeks had shown antibodies. Secondly, scientists have little idea how long people remain immune.
Long-term research by Columbia University found that for many better-understood types of coronavirus, "immunity seems to wane quickly".
Child infectiousness
The extent to which children pass Covid-19 on is also being debated.
Last week, a review of evidence in partnership with the Royal College of Paediatrics and Child Health said no child had been found to have passed coronavirus to an adult. It concluded that children "do not play a significant role" in spreading the virus and are far less likely to become infected than adults.
In all the contact-tracing from the early days of the pandemic, there was not one case of the virus being passed from a child to an adult.
However, Public Health England is still trying to establish whether children transmit the virus.
Last month, a German study suggested that even though children tended to have far milder symptoms than adults, those infected seemed to have the same levels of circulating virus in their body as adults.
