On 1 February, there was joy in South Africa when one million doses of the Oxford/AstraZeneca coronavirus vaccine arrived in the country. On 6 February, the health minister announced that the rollout of the vaccine would be put on hold after a small study suggested it does not prevent mild or moderate illnesses caused by the B.1.351 variant responsible for almost all covid-19 cases in the country.
“These results are very much a reality check,” Shabir Madhi at the University of the Witwatersrand said during a video conference on 7 February announcing the findings.
The finding is worrying, not least because the B.1.351 variant is now spreading in several other countries including the UK and US, though so far the number of detected cases outside South Africa remains very low. The UK has stepped up testing to try to halt its spread.
What’s more, it also appears past infection by other coronavirus variants confers no protection against mild or moderate infections by B.1.351, said Madhi. In a study of people given a placebo during a trial of the Novavax vaccine, the infection rate was just as high in those who tested positive for antibodies as in those who had none.
However, it is likely that the Oxford/AstraZeneca vaccine does still protect against severe disease due to the B.1.351 variant, he Madhi. While he did not say so, it is therefore possible South Africa will decide to give the doses it has to high-risk groups, instead of to front-line healthcare workers as originally planned.
Madhi also pointed out that some other vaccines have already been shown to be effective against B.1.351. “It’s not all doom and gloom,” he said.
The Oxford/AstraZeneca vaccine is effective against most other variants, including the fast-spreading B.1.1.7 variant first detected in the UK. An analysis of results from ongoing trials in the UK suggests the vaccine is around 74 per cent effective at preventing symptomatic infections due to B.1.1.7, compared with 85 per cent for other variants.
A separate analysis of ongoing trials in the UK, Brazil and South Africa concluded that a single dose of the Oxford/AstraZeneca vaccine is 76 per cent effective at preventing symptomatic infections between 22 and 90 days after vaccination. A second dose 12 weeks or more after the first boosts this to 84 per cent.
Unfortunately, the results from one small ongoing trial of the Oxford/AstraZeneca vaccine in South Africa are not so good. The trial began in June last year, and data from the first months suggest the vaccine was around 75 per effective at preventing mild or moderate cases. There were no severe cases, as most volunteers were young and healthy.
But once B.1.351 started becoming the dominant strain in October, there was no statistically significant difference between those given the vaccine and those given a placebo, Madhi said. In other words, it seems the vaccine is not effective against B.1.351, but because the numbers are so low – just 1750 volunteers and 42 symptomatic cases – there are huge uncertainties.
The good news is that South African trials of the coronavirus vaccines made by Novavax and Johnson & Johnson show that while they are less effective against B.1.351 than other variants, they are both still around 60 per cent effective at preventing mild or moderate infections.
Crucially, the Johnson & Johnson one-dose vaccine is even more effective against severe disease. It is 85 per cent effective at preventing severe or critical covid-19 in all countries where it is being trialled, with no decline due to B.1.351, said Glenda Gray, also at the University of the Witwatersrand. We do not yet know the equivalent figure against B.1.351 for any other vaccine.
The greater efficacy against severe disease may be because while B.1.351 is able to evade antibodies that prevent infection in the first place, it cannot dodge the T-cells that help mop up infections.
The Johnson & Johnson vaccine has not yet been approved for use anywhere in the world, but the plan is now to greatly expand the ongoing trial in South Africa to include healthcare workers, said Gray.
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