A coronavirus vaccine being developed at the University of Oxford is safe and induces an immune reaction, preliminary results of the study show.
Researchers say their tests have revealed that the jab could provide double protection against Covid-19.
The early stage trial found that the vaccine is safe and causes few side effects.
It also 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.
Compared with the control group of those given a meningitis vaccine, the coronavirus vaccine caused minor side effects more frequently, according to the study.
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But some of these could be reduced by taking paracetamol, the researchers said, adding that there were no serious adverse events from the vaccine.
Co-author 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.’
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, published in The Lancet, 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.
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 wrote: ‘We have already ordered 100 million doses of this vaccine, should it succeed.
‘Congratulations to the scientists at @UniofOxford & @OxfordVacGroup and leadership of @AstraZeneca.’