Abstract
An early trial of a vaccine candidate from the University of Oxford has produced a promising immune response, reports Michael Le Page
AN EXPERIMENTAL coronavirus vaccine developed at the University of Oxford produces the hoped for immune responses in people. Even though it isn't yet clear if this means the vaccine will prevent infections, the group that made it has struck deals for companies to make 2 billion doses of it within a year.
“It's a really important day today,” says team leader Sarah Gilbert. “But there's still a long way to go.”
At least 23 experimental vaccines are being tested in people. The aim of these trials is to prove that the vaccines work, but that will take time, because it requires giving the vaccine or a placebo to many thousands of people in a region where there are lots of coronavirus cases.
The latest findings were the result of a smaller trial intended to study the immune response to find out if the vaccine is safe and produces the intended effect. About 1000 volunteers were given the Oxford vaccine, which uses a chimpanzee cold virus to deliver the gene for the coronavirus spike protein to human cells.
The modified virus can't replicate, so can't cause infection itself. No serious adverse effects were reported in the study, published this week (The Lancet, doi.org/gg5gwk).
The volunteers did generate lots of antibodies, proteins that circulate in the blood and bind to viruses. Not all antibodies bind in a way that renders the virus harmless, but after one dose most volunteers produced neutralising antibodies, which do prevent viruses infecting cells. After two doses, all the volunteers generated neutralising antibodies.
Their bodies also made immune cells known as T-cells that seek out and destroy infected cells before they produce more viruses. This cellular response is thought to be an important part of immunity to the coronavirus. “We are super-excited by these results,” says team member Teresa Lambe.
The antibody response is comparable to that seen in natural infections, but the cellular response is stronger. However, it remains to be seen whether this response is sufficient to protect against infection and how long this protection lasts.
Even if immunity fades fast when people are infected with the coronavirus itself, that doesn't necessarily mean vaccine-induced immunity will do the same, says team member Adrian Hill. “It's wrong to assume that,” he says.
It is also unclear how well the vaccine will protect older people, who are at greater risk from covid-19 and have a smaller response to flu vaccines. The Oxford trial involved only people aged between 18 and 55.
After two vaccine doses, all the volunteers produced antibodies that prevent viruses infecting cells
In a paper published alongside the Oxford one, a team in China reported results from a trial in which 603 volunteers were given a dose of a similar vaccine, called Ad5. It found that the immune response was lower in people aged over 55 (The Lancet, doi.org/gg5gwj).
These studies aren't the first of their kind. US company Moderna has found that its experimental vaccine provoked protective responses in 45 people. It has now entered into larger, phase III trials.
The Oxford team is also entering larger trials. About 8000 people in the UK have already been given the vaccine, and the trial is being extended to include people over the age of 55. Trials are also starting in the US, Brazil and South Africa. Because the number of covid-19 cases are higher in these countries, these trials may yield results sooner.
Pharmaceutical firm AstraZeneca is already gearing up to produce 1 billion doses of the Oxford vaccine, and the Serum Institute of India has also agreed to make a billion. These will be produced on a non-profit basis while the pandemic lasts.
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