A major breakthrough in the search for a coronavirus vaccine, with a jab found to be more than 90pc effective, has been hailed as a potentially game-changing development by a Norwich-based expert in infectious diseases.

Pharmaceutical giant Pfizer and its partner BioNTech said interim results showed their jab could prevent people developing Covid-19.

The vaccine has been tested on 43,500 people in six countries and no safety concerns have been raised, with the companies planning to apply for approval to use it by the end of the month.

Prime minister Boris Johnson’s official spokesman said: “The results are promising and while we are optimistic of a breakthrough, we must remember there are no guarantees.”

Microbiologist Prof Paul Hunter, from the University of East Anglia, said: “I am actually quite excited about this, to be honest.

“There are provisos. This is the interim analysis which may or may not hold out in the final analysis and I’m always a bit cautious in what companies put out in press releases, which will need to be properly peer-reviewed in journals.

“But it sounds promising and I’m a lot happier than I was.

“Some of the other vaccines have been about making infections less severe, but what they are saying is this vaccine actually prevents infection.

“If that is the case, it would have a big impact, not just on people who have got the infection, but depending on how many people get the vaccine, on those who have not, as it has the potential to reduce transmission.”

Prof Hunter said, if the vaccine does get the go-ahead for public use, then health workers and people in care homes were likely to be first to get jabs.

And he said: “Another issue is how long it lasts. I don’t know for sure, but my guess it that it will last for at least a year.

“If it does, then it would be a case of getting vaccinated every year, like with flu jabs.”

Dr Albert Bourla, Pfizer chairman and chief executive, said: “Today is a great day for science and humanity.”

He said: “The first set of results from our Phase three Covid-19 vaccine trial provides the initial evidence of our vaccine’s ability to prevent Covid-19.”

He added: “We will continue to collect further data as the trial continues to enrol, for a final analysis planned when a total of 164 confirmed Covid-19 cases have accrued.

“I would like to thank everyone who has contributed to make this important achievement possible.”

Peter Horby, professor of emerging infectious diseases and global health at the University of Oxford, said: “This news made me smile from ear to ear.”

He added: “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.”

Pfizer and BioNTech expect to be able to produce up to 50 million vaccine doses globally in 2020 and up to 1.3 billion doses in 2021.

The data from the full trial will be submitted for scientific peer-review publication.

The figures presented so far are based on the first 94 volunteers to develop Covid-19.

The overall effectiveness of the vaccine may change when the full results are released.

The vaccine has been shown to produce both an antibody and T-cell response in the body to fight coronavirus.