Scientists who conducted a small-scale trial of the vaccine’s efficacy said it showed very little protection against mild to moderate infection, though they expressed hope that – in theory – it would still offer significant protection against more serious infection.
South Africa has halted the rollout of the Oxford/AstraZeneca jab, while a UK health minister indicated that an annual Covid jab could become the norm for many people as scientists work to stay a step ahead of the virus’s mutations.
Prof Shabir Madhi from the University of the Witwatersrand, who led the trial, said that, while the study was small, it was designed to focus on determining whether or not the vaccine had at least 60% efficacy against Covid to any degree of severity.
“The results that we now describe against the variant, the point estimate is 10%. Clearly, that is far off the 60% mark and, even if you had a larger study you are unlikely to get to a vaccine efficacy readout of even 40 or 50%,” he told BBC Radio 4’s Today programme.
“What the study results really tell us is that, in a relatively young age group demographic – with very low prevalence of morbidities such as hypertension and diabetes etc – the vaccine does not protect against mild to moderate infection.”
He said its effectiveness against serious infection could possibly be inferred based on the Johnson & Johnson vaccine, which uses “similar technology”. “Extrapolating from that, there’s still some hope that the AstraZeneca vaccine might well perform as well as the Johnson & Johnson vaccine in a different age demographic that are at highest risk of severe disease,” he said.
He added that laboratory studies could reveal it is not just antibodies that are effective in protecting against severe disease, but also T-cell immunity. On the issue of delaying the second dose, he said the Oxford vaccine efficacy after a single dose was 75% but this was before the South African variant arose.
The news has caused concern that the vaccines now available will prove insufficient to end the crisis on their own and manufacturers are already working on new versions that will offer protection against variants.
On Monday the UK health minister Edward Argar acknowledged there would be a need for booster shots. “What we would all expect is every year we have our flu booster jabs, or our flu jabs, it would not be unreasonable to suggest something similar here,” he told Sky News.
He added that the virus “will always try to outwit us”, saying: “We’ve just got to make sure we get ahead of the game and we outwit it.”
Argar said the results of the trial did not show the vaccine was ineffective at reducing the severity of the illness people would experience, telling Sky: “There is no evidence that this vaccine is not effective in preventing hospitalisation, severe illness and death, which is ultimately what we’re seeking with these vaccines.”
He said the “dominant strains in this country are not the South African strain”, telling the Today programme the latest figures showed 147 cases of that variant in the UK.
But he acknowledged the danger that new variants could develop with similar resistance, thereby reducing the effectiveness of the UK’s vaccination programme and meaning the work by scientists to stay a step ahead would need to continue for the foreseeable future.
