Nobody can be “completely certain” that it is possible to find a vaccine for Covid-19, but the prospects are “very good”, according to a scientist who is leading a team attempting to develop one.

Sarah Gilbert, Professor of Vaccinology at Oxford University, said they hope to begin clinical trials towards the end of next week.

And she said that alongside these trials, preparations need to be made to manufacture the vaccine in large amounts.

Prof Gilbert told the BBC’s Andrew Marr Show that trials need to be done to see if it is possible to find a workable vaccine.

“The prospects are very good, but it is clearly not completely certain,” she said.

Prof Gilbert said her team is currently waiting for final safety tests and final approvals for clinical trials to start.

In the meantime, permission has been given to recruit volunteers, take blood tests, explain the process and check their health status, she said.

Prof Gilbert said: “By the time we have all the approvals for the vaccine ready, we should have a good pool of volunteers to draw from and we should be able to get going quite quickly.”

It is difficult to know when a vaccine might be ready, Prof Gilbert said, as there are many complex stages in vaccine development.

These start with immunising healthy 18 to 55-year-olds, before moving into older age groups, looking at the safety and immune response to the vaccine.

“That’s important because it’s the older population that we really need to protect with the vaccine,” she said.

“But with vaccines in general, you get not so good immune responses as the immune system ages, so we need to find out with this vaccine how good it’s looking in older people compared to younger people, just by measuring the immune response to the vaccination.”

Half of all the trial volunteers will get the new coronavirus vaccine and the other half will get a vaccine licensed to protect against meningitis. Volunteers will not know what they are given, she said.

“Over time, as people become infected, or have symptoms of coronavirus, they will come to us to get tested, and we will arrange to have them tested very quickly and when enough people have become positive for the coronavirus, the statisticians will look at which groups those people were in, to find out ‘were they in the group that had the coronavirus vaccine or are they all in the group that had the meningitis vaccine?’.

“Obviously we’re hoping for the infections only to happen in the meningitis vaccine group. And if that’s the case we will then be able to say that this vaccine works, at least in the age range that we’ve vaccinated.”

Scientists need to be able to demonstrate the vaccine works, and that is affected by how much virus transmission there is at the time testing is happening.

Prof Gilbert said: “Obviously we’re seeing a drop in hospital admission now, probably a drop in virus transmission in the community, and that’s great for the population as a whole.

“It makes vaccine testing more difficult though, because we need a small number of people to become infected, and it really is a very small number, in order to know that the vaccine’s actually working.”

In addition, there needs to be preparation to manufacture large amounts of doses.

“What we need from government is support to help us accelerate the manufacturing,” she said, adding that there are no manufacturing facilities in the country that can do so at the moment.

There is a plant at Oxford University that can make small amounts of doses, which will be used for the first clinical trials, Prof Gilbert said, but this “needs to go to a much bigger scale”.

Companies involved in manufacturing the vaccine will need to have trained staff and new equipment, she said.

“And all of that can happen but the companies that we’re going to be working with are going to need to stop doing what they would normally do and make this vaccine instead,” she added.

Prof Gilbert also said that Oxford is not looking to make money out of the vaccine, adding they are concentrating on making it available for public health use.

“The university is looking to protect people’s health,” she said. “And to do that as widely as possible across the world. It’s not just for this country, we need to make a vaccine for the world.”

Discussions are going on about fair access to all vaccines that work at a global level, she added.

Prof Gilbert said her team has gone through stages of vaccine development that usually take five years in just four months.

Sir Jeremy Farrar, a member of the Government’s Scientific Advisory Group for Emergencies (Sage), said he was “optimistic” about finding a vaccine but that finding a safe and effective treatment for the latest strain was “not a given”.

He told Sky News’s Sophy Ridge On Sunday: “I hope we would have a vaccine towards the end of this year – but that’s a vaccine in a vial, it’s a vaccine that we believe to be safe, a vaccine we think might be effective.

“I think it’s crucial to realise having a vaccine in itself, in say a million doses, which you know to be safe and you believe to be effective. That is not the end game.

“The end game is making sure that it is truly effective. It’s effective in the elderly, effective in young children, effective right across the age group in all populations.

“And then you have to manufacture that in billions of doses to administer them to the world.”