Moderna released crucial data on its blockbuster Covid jab under embargo before the results were made public, sparking calls for new rules over how vaccine trial information is announced to the market.
The US drugmaker briefed journalists on data showing its jab is almost 95pc effective against coronavirus, almost an hour before publishing the details.
Its public announcement at 11.56am sent the FTSE 100 surging more than 1pc in minutes on a wave of optimism. On Wall Street, the S&P 500 climbed 0.7pc towards a new closing high while shares also clocked up gains in France, Germany and Italy. The London index closed up 1.7pc on the day.
There is no suggestion Moderna broke any rules. The vaccine news landed in journalists' inboxes with a midday embargo, meaning this lifted before US trading opened.
The move has sparked debate on how market-shifting information about a potential vaccine is disseminated against a backdrop of a global pandemic.
Embargoes are seen as useful because they allow the media to prepare news stories ahead of major announcements, but some market watchers said they pose a risk of leaks if data can move share prices.
One analyst said UK-based companies would be unlikely to release this sort of information under embargo.
They said: "It's a strange thing to do. There is no way you would send out a release that was market sensitive in the UK without the full checks and balances in place.
"If I was going to send something this sensitive, it would be via the regulatory news service so everyone has it at the same time."
A former trader said: "You are relying on the trust of the recipients not to break the embargo.
"It is possible somebody could pick up the phone. We knew that Moderna's release was imminent, we were all expecting it and I have been checking it every day."
Mark Bentley, a board member of ShareSoc, which represents individual shareholders, called on the Financial Conduct Authority (FCA) to look into the practice of companies releasing market-moving information under embargo.
Institutional investors can use leaked information to inform decisions and this could be damaging to individual shareholders who effectively end up on the other side of those trades, he said. There is no evidence of leaks in this case.
Mr Bentley said: "Market-sensitive information being disseminated widely, even with embargo warnings on it, is a risk and I think it's something the FCA should have a look at.
"An embargoed press release can be distributed very widely. And obviously, with that many people having access to it, it's virtually certain to leak before the embargo time."
Jet engine maker Rolls Royce ended Monday almost 10pc higher on hopes of a revival for holidays and air travel, with similar rises for British Airways owner IAG and Premier Inn owner Whitbread.
Shares also rose in other big companies whose prospects depend on vaccines allowing life to return to normal. They included British Land, engineers Melrose and Smiths Group and office caterer Compass.
However, companies that have benefited from people staying home during the pandemic such as Just Eat Takeaway.com and Ocado suffered falls.
Maxim Jacobs, managing Partner and research director for Edison Group, said: "Once we get to spring, Covid-19 is going to be a thing of the past for the most part as these vaccines will enable a return to normalcy."
Moderna shares soared as much as 15pc in New York before paring gains to be more than 7pc higher in afternoon trading at $96. The stock was worth $19 at the start of the year.
Like a vaccine by rival Pfizer which sent markets surging with similarly promising pre-trial results last week, the Moderna jab uses mRNA to teach the body's cells to recognise and fight the covid virus.
Results from the clinical trial suggest the vaccine is nearly 95pc effective, with no serious side effects. This is impressive by any standard in the pharmaceutical industry, but the trial is not yet completed and about a fifth of drugs fail at the final hurdle.
There are 30,000 patients in Moderna's clinical trial, but the interim data is only based on 95 patients, 15 of whom were over the age of 65.
In contrast with Pfizer, the Moderna vaccine can be stored in a standard freezer at minus 20c for up to six months, in a refrigerator for up to 30 days and at room temperature for up to 12 hours. This means it could be much easier to distribute and administer.
The company will apply for regulatory approval and could have 20m doses ready to ship in the US by the end of the year. It hopes to manufacture between 500m and 1bn doses globally in 2021.
"This is a pivotal moment ... this positive interim analysis from our phase three study has given us the first clinical validation that our vaccine can prevent COVID-19 disease, including severe disease," said Stéphane Bancel, chief executive of Moderna.
The news also comes at time when Covid cases are soaring, hitting new records in the United States and pushing some European countries back into lockdowns.
Moderna did not comment.