When news emerged last month of a new, far more contagious mutation of coronavirus spreading across Britain there was only one positive straw at which to clutch.
There was no evidence, said scientists, that the “Kent” variant was more deadly than the original strain.
On Thursday morning, the Prime Minister was shown a paper by the Government’s Nervtag [New and Emerging Respiratory Virus Threats Group] which appeared to destroy even that shred of hope.
It considered three studies, which suggest that as well as being remarkably contagious, it is also significantly more fatal - between 30 and 90 per cent more so.
Scientists don’t know why.
But they think it may be that some of the behaviours which make the variant more easy to transmit, may also make it more lethal.
Key among them is the stickiness of the mutation, and the way it gets into cells, and replicates.
Chief scientific adviser Sir Patrick Vallance told a Downing Street briefing: "It may be that it binds more solidly to the receptor for the virus and gets into cells more easily as a result.
"It may be that it grows more readily in certain cell types. Those are things that people are looking at and more information will come.
"What we can conclude is that there must be some mechanism by which it can actually bind or enter cells somehow."
Research suggests the Kent variant has other hallmarks, such as a higher viral load than the original strain.
But Sir Patrick said that so far, it does not seem that this is likely to be the reason the virus is more deadly.
However, the Nervtag paper shows that findings from different studies are not uniform.
And Sir Patrick stressed that there is “a lot of uncertainty” about those numbers.
In the paper, scientists from the London School of Hygiene and Tropical Medicine, and those from Imperial College London both suggested that the new variant was associate with a rise in mortality of around one third.
But a third paper by the University of Exeter, which matched those with the new variant to those of a similar demographic, went even futher, suggested that the Kent strain might increase mortality by 91 per cent,
On Thursday the country’s chief scientific adviser was at pains to point out that the evidence about increased mortality risks “is not yet strong”.
And he said that Nervtag’s experts had suggested the increased risk of one third was the most likely of the scenarios.
If 1,000 men in their 60s got the old variant, around 10 might be expected to die - but this would rise to 13 or 14 with the new type, he suggested, once again stressing “these things are currently uncertain.”
He was more confident, however, that vaccines will still protect against the dominant new variant, with increasing evidence that those who were infected against the first strain appeared to be protected against the new strain.
But Sir Patrick said the same could not be said about mutatations from South Africa and Brazil which are causing alarm in government.
On Thursday, it emerged that the Health Secretary has raised fears that the South African strain may be 50 per cent less effective to current vaccines.
“We are more concerned that they have certain features which means they might be less susceptible to vaccines,” Sir Patrick said yesterday.
When it comes to the Kent strain, the biggest caveat on all of the numbers is the size of the samples. Because of the way Britain’s testing system works, they only cover about 8 per cent deaths in recent weeks.
And some of the findings Nervtag considered were extremely contradictory, with no increase in death risks found when only hospitalised patients were considered.
Meanwhile, research into the new strain continues, including studies which suggest the variant may respond less well to treatments.
While the race to vaccinate the most vulnerable continues, there is a desperate need too to plug the gaps in the knowledge about the new threats, without rushing to the wrong conclusions.
Prof Neil Ferguson, the Imperial College scientist whose modelling triggered the country’s first lockdown, has urged some caution.
He told Channel 4 News: “The reason for the caution is we only really know the outcome of infection, whether people get hospitalised or whether people die, in a minority of cases.
Of everybody who dies, we know whether they've got the variant or not in eight per cent of cases; We see a very clear signal in those eight per cent of deaths, but know very little about that 92 per cent.”
Prof Ian Jones, Professor of Virology, University of Reading, said: “The NERVTAG report supporting the enhanced death rate attributed to variant B1.1.7 is at pains to stress that the data is limited and the conclusions preliminary.
However, an increased case fatality rate is certainly possible with a virus that has upped its game in transmission. But grim as it sounds, whether the fatality rate is 1 per cent or 1.3 per cent doesn’t really change the fact that for a minority of people this is a very dangerous virus that is best avoided.”
He was among many scientists saying the papers showed the need for strong vaccine uptake, and strict adherence to lockdown measures.
Prof Lawrence Young, Virologist and Professor of Molecular Oncology, Warwick Medical School, said more information was needed “before jumping to firm conclusions”.
In particular, he drew attention to the surprising findings that those with the Kent variant were no more likely than those with the old variant to end up being hospitalised, suggesting this could come down to a lag in available data.
Prof Paul Hunter, Professor in Medicine, The Norwich School of Medicine, University of East Anglia, said some Public Health England research, also quoted in the new paper, was still more worrying. It suggests that the mutated strain is 65 per cent more deadly.
“This is a really disappointing finding and will certainly have implications for how we manage the epidemic over coming months,” he said.