One of the leading coronavirus vaccine candidates has proven to be 90 per cent effective, marking a major breakthrough in the global race to stop the disease.
The UK's stock market surged this morning when Pfizer and BioNTech said that early results from a massive clinical trial suggest nine out of 10 people who get their jab are protected from coronavirus by it.
In an update on progress in the ongoing study, the pharmaceutical companies said that of 94 people infected with the virus so far, at least 86 of them had been in the placebo group, reports dailymail.co.uk.
The placebo group is one in which people are given a fake vaccine so that what happens to them can be compared with those who get the real thing. Pfizer's trial has split the participants half and half across the placebo and vaccine groups.
The company's chairman hailed the breakthrough a 'great day for science' while independent experts said the results are 'excellent' and 'really impressive'.
Pfizer and BioNTech are expected to apply for approval to give out the jab in the US as soon as possible, but they must wait for long-term safety data to be completed.
Shortly after the news broke, Downing Street announced Boris Johnson would hold a TV briefing at 5pm this afternoon.
The vaccine is one of at least seven that have already been pre-ordered by the UK Government, which has secured a deal for 30million doses of it. The jab has to be given in two instalments so the UK's current order could cater to 15million people.
Stocks surged on the news, with Britain's FTSE 100 index rising 247 points - five per cent - at around midday, with more than £83billion added to its total value today. And Pfizer's listing on the French exchange increased by 14 per cent, while its shares in New York were up more than 12 per cent in pre-market trading.
Pfizer and German partner BioNTech are the first drugmakers to show successful data from a large-scale clinical trial of a coronavirus vaccine.
They said that 94 people in a trial of more than 43,000 have so far tested positive for Covid-19, and that over 90 per cent of those did not receive the real vaccine.
The companies have not revealed the exact number but a 90 per cent efficacy rate suggests that no more than eight people who got the vaccine caught the virus, compared to 86 of those who received a fake jab.
Their next step is expected to be to apply for 'emergency use authorisation' in the US, for which they will have to go to the Food & Drug Administration once they have two months' worth of safety data - expected to be complete by the end of this month.
If it is approved in the US, the UK could follow suit soon after. Kate Bingham, chief of the UK's coronavirus vaccine taskforce, said earlier this month that 10million doses of Pfizer's jab could be available in Britain by January.
Scientists said today's news was a breakthrough in the global race to develop a jab to try and stop the pandemic.
Dr Paul Hunter, a medicine and infectious disease expert at the University of East Anglia, told MailOnline: 'If it holds up in the final analysis, that's a remarkably good result.
'There's always a big question of how long it will last, of course. You might need re-boosting every year, we don't know. It could all go pear-shaped still.
'Providing we get this vaccine and it is delivered as planned then it'll make a very big difference within a matter of months.'
On whether the jab could still fail despite promising early results, he added: 'It's always a possibility. Most of the time the final results are in line with the interim results but you can't guarantee it.
'I'm really pleased about this result you can almost begin to start seeing the light at the end of the tunnel. I just hope it's not an oncoming train.'
Scientists across the UK have said the results are cause for optimism but are still only early indications, so it is important to not get carried away.
The University of Oxford's Professor Peter Horby, who led the team that proved the steroid dexamethasone could save dying coronavirus patients, said: 'This news made me smile from ear to ear.
'It is a relief to see such positive results on this vaccine and bodes well for Covid-19 vaccines in general. Of course we need to see more detail and await the final results, and there is a long long way to go before vaccines will start to make a real difference, but this feels to me like a watershed moment.'
Professor Brendan Wren, from the London School of Hygiene & Tropical Medicine, said: 'A 90 per cent efficacy for a phase 3 trial is excellent for a new vaccine that could make a huge difference, but more confirmatory safety and efficacy studies are required.
'The RNA-based vaccine requires two doses and its true efficacy over a longer period of time remains to be evaluated. These are encouraging results and it is a case of so far so good.'
Professor Eleanor Riley, an immunology and infectious disease expert at the University of Edinburgh, added: 'At face value, this is exceptionally good news: a vaccine that is 90 per cent effective at preventing symptomatic cases of Covid-19 and with millions of doses available by the end of the year.
'However, the full data set on which the claim is based has not yet been released and so we don’t know exactly what has been found.
'The two companies are at pains to point out that the trial participants are ethnically diverse, which is good, but say nothing about the age of people in the trial. If a vaccine is to reduce severe disease and death, and thus enable the population at large to return to their normal day-to-day lives, it will need to be effective in older and elderly members of our society.
'We also know nothing yet about the severity of cases that were seen in the trial, whether infection or infectiousness was prevented, or how long the immunity is expected to last.
'But I think we have reason to be cautiously optimistic.'
Optimism was the reaction of the stock markets when the news broke, with the UK's FTSE surging to its highest level since August and some companies seeing boosts of more than a third.