The early stage results, published in The Lancet, found that the candidate vaccine, known as ChAdOx1 nCoV-19, provoked a T-cell response peaking 14 days after vaccination, and an antibody response within 28 days.
Andrew Pollard, chief investigator on the study, and professor of pediatric infection and immunity at Oxford University, described the results as “encouraging”. He told a briefing convened by the Science Media Centre on Monday that it was “a really important milestone on the path to the development of the vaccine”.
In the Commons, the Health Secretary, Matt Hancock, hailed the results for taking us “one step closer to finding a vaccine that can potentially save lives, all around the world”.
The trial, which has so far involved 1,077 healthy adults, caused minor side effects when compared with a control group given a meningitis vaccine. Fatigue and headache were the most commonly reported reactions.
However, there were no serious adverse events from the vaccine, the researchers said.
‘Still a long way to go’
Sarah Gilbert, lead researcher of the vaccine development program, and professor of vaccinology at Oxford, cautioned that there was still a long way to go before the team could confirm that the vaccine could protect against developing COVID-19.
“The difficulty that we have, and that all vaccine developers have in trying to make a vaccine against this particular virus, is that we don’t know how strong that immune response needs to be,” she said.
“So, we can’t say just by looking at immune responses whether this is going to protect people or not. And the only way we’re going to find out is by doing the large phase 3 trials and wait for people to be infected as part of that trial before we know if the vaccine can work.”
The authors noted some limitations to their findings. They said more research was needed to confirm their results in different groups of people – including older age groups, those with other health conditions, and in ethnically and geographically diverse populations.
A notable result of the trial was that participants given a second dose of the vaccine appeared to display a stronger immune response, a finding that had influenced plans to “look at two dose regimes as well as one dose regimes in the phase 3 trial”, Prof Adrian Hill, director of Oxford’s Jenner Institute, confirmed.
ChAdOx1 nCoV-19 is made from a weakened version of an adenovirus that causes infections in chimpanzees. The virus has been genetically modified so that it cannot grow in humans.
On Monday, the government announced that it had struck a deal with AstraZeneca for access to 100 million doses of the Oxford vaccine, in addition to millions of doses of other promising candidate vaccines.
Expert reaction to the findings
The Medical Research Council helped to fund the trial. Executive Chair Professor Fiona Watt commented: “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.
“There is a lot that we don’t yet know about immunity to the virus that causes COVID-19. However, it seems that both antibody and T cell immunity are important, and this vaccine triggers both responses. The much anticipated next milestone will be the results of the larger trials that are happening now to find out if the vaccine will protect people from the virus.”
Jonathan Ball, professor of molecular virology at the University of Nottingham, told the SMC: “The results of the Oxford chimp adenovirus vaccine candidate show that the vaccine is able to generate antibodies and T cells in humans and these persisted for several weeks. Whilst encouraging there is still a long way to go before we can herald the arrival of a successful coronavirus vaccine.
“It is unclear whether the levels of immunity can protect against infection – that’s what the larger ongoing phase III trials are designed to test. Nor do we know if this vaccine can protect those most vulnerable to severe COVID-19 disease.”
Stephen Evans, professor of pharmacoepidemiology at the London School of Hygiene and Tropical Medicine, commented: “For the vaccine to be really useful, we not only need the larger studies conducted where COVID-19 is still occurring at a high rate, but we need to be reasonably sure that the protection lasts for a considerable time.”
He said it was also vital that people older than 55 were included in later trials.
Richard Torbett, chief executive of the Association of the British Pharmaceutical Industry, said: “Developing a vaccine is an incredibly difficult challenge; the fact that there are multiple candidates in development is hopefully a sign that the hard work will ultimately pay off.
“But we must be patient. Proving that a vaccine is safe and effective is a long process and we could still be many months away.”
This article first appeared on Medscape.com.