Vaccines are “long shots” and people should not rely on the swift development of one for Covid-19, the Government’s chief scientific adviser has warned.

A group of Oxford University researchers will begin clinical trials for a coronavirus vaccine next week but Sir Patrick Vallance says expectations need to be tempered.

Writing in The Guardian, Sir Patrick wrote: “All new vaccines that come into development are long shots; only some end up being successful, and the whole process requires experimentation.”

“Coronavirus will be no different and presents new challenges for vaccine development,” he added.

“This will take time, and we should be clear it is not a certainty.”

His warning came as Sarah Gilbert, Professor of Vaccinology at Oxford University, said her team hopes to begin clinical trials towards the end of next week.

She acknowledged nobody can be “completely certain” that it is possible to find a vaccine for Covid-19, but the prospects are “very good”.

This will take time, and we should be clear it is not a certainty

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.

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.

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.

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 also 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.”

Meanwhile, Sir Patrick has been put in charge of a Government taskforce which will support efforts to rapidly develop a vaccine as soon as possible.

As well as providing industry and research institutions with the resources and support, the group will review regulations to allow quick and safe vaccine trials.