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Africa: Why Some Scientists Think the Astrazeneca Vaccine Is Still Useful for South Africa

While the results are disappointing against the local variant of the Covid-19 virus, there are reasons to think the vaccine may reduce deaths

The government halted the roll-out of the AstraZeneca/Oxford University vaccine this week following a study led by Wits vaccinologist Shabir Madhi, which found that it did not protect against mild to moderate Covid-19 in a local trial on account of the variant of the virus, 501Y.V2, that is dominant here.

A pre-print of the study, which has not yet been peer-reviewed, was published on Friday.

What the study found

Volunteers between 18 and 65 years old were recruited from June to November last year, and given two doses of either vaccine or a placebo, three to five weeks apart. The trial was done at seven sites in Tshwane, Johannesburg and Cape Town; and participants broadly reflected the country’s population groups.

At the end of the trial 1,467 (750 vaccinees and 717 placebo) all of whom were not HIV positive, were successfully traced. Forty-two participants developed mild to moderate Covid, but no cases were serious enough to require hospitalisation, probably on account of the sample being relatively young – the average (median) age was only 31.

39 of the 42 people who contracted the virus, were infected with the new variant, 501Y.V2. Vaccine efficacy, which measures the reduction in risk for those who are vaccinated compared with those who are not, was only 10% in these 39 cases.

Also serum from a sample of vacinees who did not become infected with Covid was tested against the original and 501Y.V2 variants using a pseudovirus — a virus modified for experimental purposes — that infects cells using the spike proteins that protrude from its surface which give the coronavirus its name. (Serum is blood filtered of some of its cells, taken from people who have recovered from Covid-19.)

80% of these sera were unable to neutralize the 501Y.V2 pseudovirus. This led the authors to conclude that the vaccine had no efficacy against non-hospitalised mild to moderate Covid-19 primarily due to the new variant, compared to 75% efficacy for the original one.

Madhi said in a webinar on Tuesday that using this vaccine on all health workers in this context could not be advised, as the majority would be likely to develop only mild to moderate Covid. However, he encouraged targeted use for elder health care workers or those with comorbidities, in the context of no alternatives being available.

This is because the vaccine might still provide some protection against severe cases of Covid likely to end in hospitalization. A US trial currently in progress on the AstraZeneca vaccine is evaluating it for its effects on severe disease.

Why might the vaccine still be useful in South Africa?