Scientists behind the project described progress as “so far, so good” after 1,000 people were given the jab. Sir John Bell, regius professor of medicine at Oxford University where the trials are being carried out, said the vaccine “looks safe”. The scientists from the university’s Jenner Institute and the Oxford Vaccine Group are now eagerly awaiting signs that it can protect against Covid-19 and have started enrolling hospital workers in an effort to speed up results, as they are now more likely to be exposed to infection.
The team has agreed a partnership with AstraZeneca and hopes to produce one million doses of the vaccine by September. The Cambridge-based drugs giant has said it could scale up to 100 million by the end of the year.
Sir John, who previously suggested results could be available by mid-June, said: “They’ve got over 1,000 people vaccinated in the phase 1-2 project and so far, so good.
“It looks safe and we’re now starting to wait for an efficacy signal to see whether people who’ve been vaccinated don’t get the disease. That’s the next step.”
A study has already shown that the vaccine worked when tested on six rhesus macaques – monkeys often used in research as they share the majority of their genes with humans. Those given a single dose of the Oxford vaccine had a reduced viral load (the amount of virus in the body) and remained healthy when deliberately exposed to heavy doses of coronavirus.
Half of the human volunteers have received the CHADOX1 nCoV-19 vaccine, while the rest were given a meningitis jab.
The two produce similar side effects, ensuring no one will know which vaccine they got.
Comparing the number of people who get Covid-19 in each group will reveal whether the vaccine has worked.
However, the success of Britain’s lockdown has sparked fears that transmission may be too low for enough volunteers to naturally become infected.
Sir John said that healthcare workers are being enrolled in a bid to speed up results, as they are more likely to be exposed to the virus than the general population.
He told BBC Radio 4’s Today Programme: “The disease is on the wane and there is a risk that we won’t have enough active disease to catch people.
“The population that is still at pretty high risk are healthcare workers. So they will be moving – I think already have moved – into the healthcare worker population because there the disease prevalence is about four per cent. They should be able to get a signal from those individuals we hope.”
Jeffrey Almond, a visiting professor of microbiology at Oxford University, who is not involved in the research, said the team will be looking for evidence of neutralising antibodies in volunteers’ blood. Testing the antibodies in a lab to see if they correctly bind to the virus and stop it entering cells will give an early clue as to whether the inoculation triggered the correct immune response.
Prof Almond, who was head of research at pharmaceutical giant Sanofi for 15 years, said: “That gives you good encouragement that you might then get protection because that’s what you need to happen.
“You need your immune response to stop the virus getting into your cells, into your body and starting the infection.”
He added: “I think we can be cautiously optimistic about the efforts in the UK, with the Oxford [vaccine] being slightly ahead of pretty much everyone else, even internationally.
“If everything works out we may have a vaccine towards the end of the year in reasonable amounts.”
Some scientists have suggested conducting challenge trials, in which vaccinated volunteers are deliberately exposed to the virus to speed up results. More than 20,000 people in 102 countries have signed up online with US campaign group 1DaySooner, indicating they would be willing to take part.
The group estimated that if one sixth of the world acquires Covid-19 each year and a vaccine stopped 0.2 percent of them dying, then speeding up development by just one day could save 7,120 lives.
More than half a million could be saved worldwide if the process was accelerated by three months, they estimated.
Sir John said scientists in Oxford had “definitely had the discussion” but challenge trials were “fraught with all kinds of problems”.
He added: “If you start to think about the practicalities of this it’s really quite complicated. We’re not that far away from an answer if we just keep our heads down, I think that’s probably the safest bet.”
The update came as the European Medicines Agency said medicines to treat Covid-19 could be available before the summer and a vaccine might be approved early next year.