Scientists have cast doubts over the coronavirus vaccine being developed by University of Oxford researchers, suggesting “concerning” results of trials in macaque monkeys indicated it may only offer “partial protection”.
The government pledged a further £65.5m for the research on Sunday, announcing it had struck a global licensing deal with pharmaceutical giant AstraZeneca, which will see up to 30 million doses produced by September if the vaccine is successful.
Human trials of the ChAdOx1 nCoV-19 vaccine are already underway, after trials on mice and rhesus macaques at the US National Institute of Health’s Rocky Mountain Laboratory, the full results of which were made public last week in a non-peer-reviewed preprint.
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The researchers found a single dose of the vaccine prevented all six vaccinated monkeys from developing pneumonia, but did not prevent infection outright.
Some scientists not involved in the study welcomed the results as promising, but others also raised concerns that, if the results were replicated in humans, those vaccinated would probably still be able to transmit Covid-19.
Prof Jonathan Ball of the University of Nottingham said the results were “encouraging”, but added it was “concerning” that the same amount of virus genome was detected in the noses of both the vaccinated and unvaccinated monkeys.
“If this represents infectious virus and a similar thing occurs in humans, then vaccinated people can still be infected, shed large amounts of virus which could potentially spread to others in the community,” the molecular virologist added.
“If the most vulnerable people aren’t protected by the vaccine to the same degree, then this will put them at risk. Therefore, vaccine efficacy in vulnerable populations and the potential for virus shedding in vaccinated people needs very careful monitoring.”
Professor of Immunology and Infectious Disease at the University of Edinburgh, Eleanor Riley, agreed the levels of virus found in the monkeys’ noses were “worrying”.
“If similar results were obtained in humans, the vaccine would likely provide partial protection against disease in the vaccine recipient but would be unlikely to reduce transmission in the wider community,” she said.
However, the paper’s co-author Neeltje van Doremalen, of Rocky Mountain Laboratory, suggested that the monkeys had been exposed to a far higher viral load than most humans would be in real life.
“I think people don’t realise how much virus we challenge with and how amazing it is to see none in the lungs. After a single shot of vaccine,” Prof Van Doremalen said on Twitter.
Immunologist Florian Krammer also added: “None of the vaccines in development will work with one shot (that’s just not how vaccines work). This was after one shot. The lung was protected. Two shots might be pretty solid.”
However, award-winning virologist Paul Bieniasz, said: “To be honest, the magnitude of the immune responses in macaques is a little underwhelming – what will protection be like six or 12 months post vaccination?”
It is “unlikely” any potential Covid vaccine will be able to stop infection and offer life-long protection, said Prof Babak Javid, a infectious diseases consultant at Cambridge University Hospitals.
He pointed out it was not “without precedent” that a vaccine works by preventing a person from becoming ill, but not from becoming infected, such as the current whooping cough vaccine.
Agreeing that such a vaccine would not stop the virus being transmitted to others, Prof Babak said that he believed the potential vaccine was a worthy candidate for further development.
Others welcomed the fact that the macaque trials had found no evidence of immune-enhanced disease – a phenomenon that sees vaccinated people who do become infected end up suffering more severe illness.
The phenomenon is a hazard of vaccines for respiratory viruses, and was one of the main obstacles to a successful Sars vaccine.
“This was a definite theoretical concern for a vaccine against Sars Cov-2 and finding no evidence for it in this study is very encouraging,” said Prof Stephen Evans, of the London School of Hygiene and Tropical Medicine.
Asked whether results in macaques will likely translate to results in humans, he added: “No we don’t know for sure, that’s why trials need to be, and are being, done in humans.
“But it is encouraging to see these results and suggests cautious optimism for the Oxford vaccine trial being done in humans.”