University of Oxford researchers said tests revealed the vaccine could provide double protection against coronavirus and caused few side effects.
The early stage trial found 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.
Professor Fiona Watt, executive chairwoman of the Medical Research Council, which helped to fund the trial, said: “It is truly remarkable how fast this vaccine has progressed, with our support, through early clinical trials, and it is very encouraging that it shows no safety concerns and evokes strong immune responses.”
Shares in AstraZeneca, which has partnered with Oxford University to guarantee supply of 100 million doses of the vaccine, rose sharply on news of the successful trial.
The pharmaceutical firm closed 133p higher yesterday on the FTSE100 at 9,320p.
AstraZeneca chief executive Pascal Soriot told reporters the company hoped to deliver the vaccine by the end of the year, depending on how infection rate affected ongoing trials.
“The only way to be ready to distribute the vaccine shortly after we get the results is to manufacture in parallel to doing the clinical development,” Mr Soriot said.
“So we’re basically starting the manufacturing process in parallel to running the clinical trials.
“The question of when we’ll be able to distribute is a function of mostly, in fact, the infection rate in the community – therefore how quickly we can show efficacy.
“And then it will be in the hands of the regulators to review the data in their various geographies.
“Our hope is that we can actually start delivering the vaccine before the end of the year, and how early before the end of the year depends really on infection rates in the community.”
Oxford Professor Sarah Gilbert, the co-author of the study, 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.” She added: “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.”
UK health secretary Matt Hancock said researchers and health officials had “played a blinder” and claimed the virus was “on the back foot”.
He added that a vaccine would be made available “as soon as humanly possible”, but would not be approved by regulators “until we are clinically confident it is safe”. “The MHRA [Medicines and Healthcare products Regulatory Agency] has done an amazing job, they have, alongside the scientists, made sure the trials are designed so they can approve the results as soon as the results come forward in parallel essentially rather than afterwards, which would be the norm,” Mr Hancock told the House of Commons.
“They have played a blinder.
“They are one of the reasons why the UK is at the forefront of this on vaccines and treatments.
“That means a vaccine will be available as soon as humanely possible and as soon as the science is proven.”
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.”
And First Minister Nicola Sturgeon posted on Twitter: “Really encouraging news. Let’s all keep everything crossed.”
Compared with the control group of those given a meningitis vaccine, the Covid-19 vaccine caused minor side effects of headaches and fever, but some of these could be reduced by taking paracetamol, the researchers said.
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 the current trial, published in The Lancet, is too preliminary to confirm whether the new vaccine meets these requirements.
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.
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 23 April and 21 May.
Professor Adrian Hill, the director of the Oxford Jenner Institute that is developing the vaccine, said it was very unlikely that any immunity to Covid-19 would only be short term.
Speaking at a webinar organised by the Science Media Centre, Prof Hill said: “Making the assumption that if natural infection doesn’t give you immunity for very long therefore a vaccine won’t give you immunity for very long, that doesn’t follow.” He continued: “What matters is the type of vaccine technology you are using.
“The other upbeat response is that there aren’t really vaccines out there that just last for a few months. By and large vaccines last for some years, or at least a year and then you might need a top-up.
“[Immunity] is not going to disappear very quickly.”
Labour shadow health secretary Jon Ashworth welcomed the “encouraging and exciting” news and offered his support in tackling “poisonous anti-vax propaganda”.
But SNP health and social care spokeswoman Dr Philippa Whitford warned a widely available vaccine was “still some way off”.
Earlier, it was announced the UK Government had signed deals for 90 million doses of several promising Covid-19 vaccines, with more in the pipeline.
The latest deal is for vaccines being developed by an alliance between the pharmaceutical giants BioNtech and Pfizer as well as the firm Valneva
Valneva has a factory in Livingston, and the UK Government is expected to contribute to expanding this Scottish facility.
Kate Bingham, chairwoman of the UK Vaccine Taskforce set up to ensure sufficient supplies of a vaccine, said she was hopeful one would be available by the end of the year.
She also said the goal of the taskforce was “to ensure that any successful vaccine is distributed across the globe, so that anybody who is at risk of infection is vaccinated”.