Clinical trials for the Oxford coronavirus vaccine may have gathered enough safety and efficacy data by the end of the year, a leading scientist has said.
Comments from Professor Andrew Pollard, director of the Oxford Vaccine Group, came after England’s chief medical officer, Professor Chris Whitty, said in a statement on Saturday that he would be “quite surprised if we had a highly effective vaccine ready for mass use in a large percentage of the population before the end of winter, certainly before this side of Christmas”.
Professor Pollard told BBC Radio 4’s Today programme: “I think that Chris Whitty is quite rightly being cautious, that it could take as long as that to first of all demonstrate a vaccine works and is safe and then to go through the processes of regulators looking at that very carefully to make sure everything’s been done correctly.”
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Prof Pollard said it is “just possible” that the team could have data on the coronavirus vaccine to put before regulators this year.
Asked about the timing of a vaccine, he said: “That depends very much on the number of cases that occur in the weeks and months ahead.
“Even with 1,000 people eventually you’ll have enough information to know whether or not a vaccine works, but that could take years. So, having 20,000 people in our trials already means that that period of time will be shorter, but unfortunately I can’t quite predict the future about how many cases are going to occur.”
Prof Pollard said he hoped that 50,000 people would be involved in the clinical trial for the Oxford University COVID-19 vaccine candidate.
But he stressed that the size of the trial “isn’t really the issue”, adding: “What you need is to have enough cases accruing during the time of observation in the trials.”
“The size of the trial is critical, first of all for safety – so you want to have good evidence that, after a large number of people have been vaccinated, you’ve got good evidence or safety around the vaccine.”
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“Secondly, you want to be able to show whether the vaccine works, and the size of the trial actually is determined largely by what the attack rate of the disease is in the study population.
“And so, if you’ve got a very, very rare disease, you need an enormous trial size, in order to be able to show whether the vaccine works. But in a situation like that at the moment coronavirus, depending on which region or country you are in, the size of the trial could be smaller or bigger just depending on how many cases are happening in that community at the time.”
He added: “There are a number of trials that we’re running from Oxford here in the UK, in Brazil, and also in South Africa, and the combined size of those three trials together is around about 20,000 people, and AstraZeneca are moving forwards in their trials in the US, hoping to start enrolling 30,000 people.
“So within the trials of the vaccine that was developed here at Oxford University, we’d expect to have perhaps 50,000 or more people in the trials in total.”
On reports that the US is planning emergency authorisation for the Oxford COVID-19 vaccine, Prof Pollard said: “Emergency use authorisations are well established by regulators both in the United States and in Europe; in fact, you may be aware just this week, the US Food and Drug Administration (FDA) has granted emergency use authorisation for plasma therapy.
“So the process of going through emergency use authorisation in an emergency is well established but it still involves having carefully conducted data, just as we are collecting information about the vaccines in clinical trials that are conducted rigorously and evidence that it actually works.
“And so, for our suite of trials that we’re running from Oxford, we would expect to first of all have safety data and then evidence that the vaccine actually works.
“And before anything were to progress from there and of course it’d be AstraZeneca who would then take that forward to regulators.”
How do scientists develop vaccines for new viruses?
Vaccines work by fooling our bodies into thinking that we’ve been infected by a virus. Our body mounts an immune response, and builds a memory of that virus which will enable us to fight it in the future.
Viruses and the immune system interact in complex ways, so there are many different approaches to developing an effective vaccine. The two most common types are inactivated vaccines (which use harmless viruses that have been ‘killed’, but which still activate the immune system), and attenuated vaccines (which use live viruses that have been modified so that they trigger an immune response without causing us harm).
A more recent development is recombinant vaccines, which involve genetically engineering a less harmful virus so that it includes a small part of the target virus. Our body launches an immune response to the carrier virus, but also to the target virus.
Over the past few years, this approach has been used to develop a vaccine (called rVSV-ZEBOV) against the Ebola virus. It consists of a vesicular stomatitis animal virus (which causes flu-like symptoms in humans), engineered to have an outer protein of the Zaire strain of Ebola.
Vaccines go through a huge amount of testing to check that they are safe and effective, whether there are any side effects, and what dosage levels are suitable. It usually takes years before a vaccine is commercially available.
Sometimes this is too long, and the new Ebola vaccine is being administered under ‘compassionate use’ terms: it has yet to complete all its formal testing and paperwork, but has been shown to be safe and effective. Something similar may be possible if one of the many groups around the world working on a vaccine for the new strain of coronavirus (SARS-CoV-2) is successful.
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