There is no guarantee that scientists will be able to find a successful coronavirus vaccine, experts have warned.
Professor Sarah Gilbert from the University of Oxford, who is leading a team working to develop a Covid-19 vaccine, said no one can be completely sure it is possible.
“That’s why we have to do trials to find out,” the professor of vaccinology told the BBC’s Andrew Marr Show.
“The prospects are very good, but it is clearly not completely certain.”
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.”
Earlier this month, she said no one can make any guarantees over a working vaccine but said having one available by autumn is “just about possible if everything goes perfectly”.
An envoy for the World Health Organisation (WHO) on the coronavirus has also warned there is no certainty over whether there will be a successful Covid-19 vaccine.
“You don’t necessarily develop a vaccine that is safe and effective against every virus,” David Nabarro, a professor of global health at Imperial College London, said.
“Some viruses are very, very difficult when it comes to vaccine development,” he told The Observer. “So for the foreseeable future, we are going to have to find ways to go about our lives with this virus as a constant threat.”
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