Video report by ITV News Correspondent Rachel Younger
The Covid-19 vaccine being developed at the University of Oxford is safe and induces an immune reaction, findings of the first phases of the study suggest.
Scientists and medical researchers across the UK have welcomed the results, with tests revealing the jab could provide double protection against Covid-19.
The tests have shown the vaccine induces strong immune responses in both parts of the immune system – provoking a T cell response within 14 days of vaccination, and an antibody response within 28 days.
It did cause minor side effects more frequently compared with the control group of those given a meningitis vaccine, according to the study, but researchers added that there were no serious adverse events from the vaccine.
Professor Andrew Pollard, director of the Oxford vaccine group said the results were "very encouraging" but cautioned that much work lies ahead.
"What it shows is that the vaccine both is very well-tolerated, exactly as we'd expect with this type of vaccine," he told ITV News.
"And perhaps really importantly we are seeing exactly the right type of immune responses, which we were hoping to see.
"Both neutralising antibodies and the type of white blood cell which we think will be important in protection.
"But, of course, at this stage we haven't got the read-out of protection because that's going to take a bit longer to get."
How many doses of the vaccine would be needed?
The findings on the Oxford vaccine trial were published in medical journal, The Lancet.
The authors wrote: "Preliminary results from a phase 1/2 trial involving 1077 healthy adults found that vaccine induced strong antibody & T cell immune responses up to day 56 of the ongoing trial.
"These responses may be even greater after a 2nd dose, according to a sub-group study of 10 participants."
The current results focus on the immune response measured in the laboratory, and further testing is needed to confirm whether the vaccine effectively protects against infection.
An ideal vaccine against Sars-CoV-2 should be effective after one or two vaccinations and work in target populations including older adults and those with other health conditions, researchers say.
They add that it should confer protection for a minimum of six months, and reduce onward transmission of the virus to contacts.
However, the experts warn that the current trial is too preliminary to confirm whether the new vaccine meets these requirements.
Phase two – in the UK only – and phase three trials to confirm whether it effectively protects against the virus are taking place in the UK, Brazil and South Africa.
The trial included 1,077 healthy adults aged 18-55 years with no history of Covid-19, and took place in five UK hospitals between April 23 and May 21.
The data included in the paper covered the first 56 days of the trial and is ongoing.
The participants either received the new vaccine (543 people), or the meningitis vaccine (534 people).
Some of them – 56 given the vaccine, and 57 in the control group – were also asked to take paracetamol before and for 24 hours after their vaccination to help reduce vaccine-associated reactions.
All volunteers gave additional blood samples and underwent clinical assessments to determine if the vaccine was safe and whether it provoked an immune response.
The most commonly reported reactions were fatigue and headache, but some participants also reported pain at the injection site, muscle ache, malaise, chills, feeling feverish, and high temperature.
In addition, in the 10 people who received the extra dose of the Covid-19 vaccine, side effects were less common after the second dose.
Professor Sarah Gilbert, of the University of Oxford, said: “There is still much work to be done before we can confirm if our vaccine will help manage the Covid-19 pandemic, but these early results hold promise.
“As well as continuing to test our vaccine in phase-three trials, we need to learn more about the virus – for example, we still do not know how strong an immune response we need to provoke to effectively protect against Sars-Cov-2 infection.
“If our vaccine is effective, it is a promising option as these types of vaccine can be manufactured at large scale.
“A successful vaccine against Sars-Cov-2 could be used to prevent infection, disease and death in the whole population, with high-risk populations such as hospital workers and older adults prioritised to receive vaccination.”
Prime Minister Boris Johnson tweeted: “This is very positive news. A huge well done to our brilliant, world-leading scientists & researchers at @UniofOxford.
“There are no guarantees, we’re not there yet & further trials will be necessary – but this is an important step in the right direction.”
Health Secretary Matt Hancock said the update on the vaccine was “very encouraging news”.
He tweeted: “We have already ordered 100 million doses of this vaccine, should it succeed.
“Congratulations to the scientists at @UniofOxford & @OxfordVacGroup and leadership of @AstraZeneca.”