LIFE will return to normal by spring, a top scientist has suggested, after the announcement by pharmaceutical giant Pfizer of a major breakthrough in securing an effective vaccine against coronavirus.

But other scientists and politicians have reacted more cautiously.

The vaccine has been tested on 43,500 people in six countries and no safety concerns have been raised.

Boris Johnson’s spokesman described the development of the jab as “promising” but stressed, as yet, there were no guarantees of an end to the pandemic.

Sir Keir Starmer, the Labour leader, tweeted: "This is really encouraging news."

The FTSE 100 jumped more than 5.5 per cent on the announcement, adding £82 billion to the value of its shares in the market's best day since March.

This afternoon, the Prime Minister will hold a Downing St press conference alongside Professor Jonathan Van Tam, England’s Deputy Chief Medical Officer, to respond to the latest development and give details of the take-up of the mass testing programme in Liverpool.

UK Government scientist Sir John Bell, Professor of Medicine at Oxford University, suggested the new vaccine would mean "life will return to normal by spring" but other scientists were more guarded in their response to the announcement by pharmaceutical giant Pfizer that the jab was found to be more than 90 per cent effective.

Commenting on the vaccine breakthrough, Sir John, a member of the Government's vaccine taskforce, told the BBC: "I am really delighted with this result; it shows that you can make a vaccine against this little critter. Ninety percent is an amazing level of efficacy.

"It rolls the pitch for other vaccines because I can't see any reason now why we shouldn't have a handful of good vaccines."

Asked if life would return to normal by the spring, Prof Bell replied: "Yes, yes, yes. I am probably the first guy to say that but I will say that with some confidence."

Prof Chris Whitty, England's Chief Medical Officer, said the news was reason to feel optimistic.

He tweeted: "Preliminary news that the Pfizer/BioNTech vaccine is effective demonstrates the power of science against Covid. We must see the final safety and efficacy data but it is very encouraging.

"It is essential we continue to suppress Covid, but it is a reason for optimism for 2021," he added.

Professor Azra Ghani, chair of infectious disease epidemiology at Imperial College London, said that long-term efficacy data would come over coming weeks and months.

Prof Ghani said: “These new results represent the first demonstration of substantial efficacy of a vaccine candidate against Covid-19 disease, which is very welcome news.

“The efficacy estimate is based on seven days of follow-up of participants following the second dose; further data in the coming weeks and months will provide a better picture of longer-term vaccine efficacy.”

David Nabarro, co-director of Imperial College London’s Institute of Global Health Innovation, said “any promising news about a vaccine is great news” but cautioned that there is still some way to go.

He told the BBC: “Everybody who’s hearing and watching this will be saying ‘wow, does this mean that life can go back to normal in the near future?’ Life will go back to a new normal, and we’re not there yet.

“We do need to be following through on all the basic rules that we now know are important for dealing with this virus; our own behaviour, the way in which governments run their health systems, and also unity between nations.

“And I just want to stress that these principles that we’ve been working for over the last 10 months are still absolutely essential.”

Dr Nabarro added: “Even if a vaccine arrives in the near future we’ve got many months of still dealing with the virus as a constant threat that we’ve got to make certain that we continue to do all that is necessary to solve the virus causing major problems. The vaccine will help, but it’s not going to be a complete game changer.”

Michael Head, senior research fellow in global health at the University of Southampton, said: “This cautiously sounds like an excellent result from the phase three trials. But we should remain a little cautious.

“If the final results show an effectiveness of anywhere near 90% with response in elderly and ethnic minority populations, that is an excellent result for a first generation vaccine.”