Oxford Covid vaccine has 10% efficacy against South African variant, study suggests

This article is more than 2 months old

Small-scale trial of vaccine shows it offers very little protection against mild to moderate infection

A healthworker prepares a dose of the Oxford/AstraZeneca vaccine
Scientists still hope the vaccine can offer significant protection against more serious Covid infection. Photograph: Alain Jocard/AFP/Getty Images
Scientists still hope the vaccine can offer significant protection against more serious Covid infection. Photograph: Alain Jocard/AFP/Getty Images

First published on Mon 8 Feb 2021 04.38 EST

The Oxford/AstraZeneca vaccine offers as little as 10% protection against the Covid variant first seen in South Africa, researchers have suggested.

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.

The disappointing results came as lab tests on the Pfizer/BioNtech vaccine found it may still provide substantial protection against the variant. Scientists at the University of Texas medical branch collected antibody-containing blood plasma from 20 people who recently had two shots of the Pfizer/BioNTech jab.

In tests, the antibodies were on average 81% as effective at neutralising the engineered virus as they were at blocking older variants. The results, reported in Nature Medicine, suggest the variant’s key mutation, known as E484K, does not dramatically undermine the vaccine’s protection.

South Africa has halted the rollout of the Oxford/AstraZeneca jab in the wake of the trial, the results of which are awaiting publication and peer review, 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 Oxford/AstraZeneca trial in South Africa, 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.

Quick Guide

Vaccines: how effective is each one?



Country US/Germany

Efficacy 95% a week after the second shot. Pfizer says it is only 52% after the first dose but the UK’s Joint Committee on Vaccination and Immunisation (JCVI) says this may rise to 90% after 21 days.

Doses Clinical trials involved two doses 21 days apart. The UK is stretching this to 12 weeks.


Country UK

Efficacy 70.4% 14 days after receiving the second dose. May have up to 90% efficacy when given as a half dose followed by a full dose. No severe disease or hospitalisations in anyone who received the vaccine. 

There have been concerns it is less effective against the South African variant of the coronavirus, and that a rare type of blood clot can be a side effect.

Doses Two, four to 12 weeks apart


Country US

Efficacy Phase 3 trial results suggest 94.1%.

Doses Two, 28 days apart


Country US

Efficacy Phase 3 trials suggest 89.3%.

Doses Two

Janssen (part of Johnson & Johnson)

Country US

Efficacy 72% in preventing mild to moderate cases in US trials but 66% efficacy observed in international trials. 85% efficacy against severe illness, and 100% protection against hospitalisation and death.

Doses: One, making it unique among Covid vaccines with phase 3 results so far


Country China

Efficacy Unclear. Researchers in Brazil have found the efficacy of the Chinese vaccine to be as low as 50.4%, whereas Turkish officials reported interim data from trials showing efficacy was 91%.

Photograph: Stéphane Mahé/X02520
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“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.

Boris Johnson says border controls are most effective when Covid rates are lower – video
Boris Johnson says border controls are most effective when Covid rates are lower – video

However, Boris Johnson said he was “very confident” in the coronavirus vaccines being used in the UK. During a visit to a vaccine test facility in Derby, the prime minister said: “We’re very confident in all the vaccines that we’re using. And I think it’s important for people to bear in mind that all of them, we think, are effective in delivering a high degree of protection against serious illness and death, which is the most important thing.”

Earlier the UK health minister Edward Argar acknowledged therewould 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.

This article was amended on 9 February 2021 to clarify that Prof Mahdi led the Oxford/AstraZeneca vaccine trial, and to include reference to that study awaiting publication and peer review.

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