Early in February, the South African government suspended the AstraZeneca vaccine rollout after a small-scale trial found that the vaccine’s efficacy against the coronavirus variant (B.1.351) first identified in South Africa was highly reduced.
Now, a new study, published today in NEJM, found that the AstraZeneca vaccine might offer as little as 10% protection from developing mild to moderate COVID-19 infection caused by the South African variant.
Scientists conducted a double-blind, placebo-controlled trial across multiple hospitals in South Africa to assess the AstraZeneca vaccine’s efficacy. Participants were randomly divided into two groups and administered two doses of either the vaccine or placebo.
A similar number of participants in the two groups contracted the COVID-19 infection, with the vast majority of cases caused by the B.1.135 variant.
The study involved less than 1500 volunteers, between 18 and 65 years old.
“A larger study population would be preferable to draw robust conclusions from,” says Dr Adam Taylor, a virologist and researcher at the Menzies Health Institute Queensland at Griffith University. “Also, the study did not involve anyone over the age of 65 who are most at risk of severe COVID-19, so they are an important population to understand when investigating vaccine efficacy,” he says.
Taylor says it’s “disappointing” that the vaccine provides minimal protection against mild and moderate disease. But he points out that the study does not address the level of protection against severe COVID-19 infection, which is more likely to require hospitalisation or lead to death.
The results came as doubts about other vaccines’ efficacy against more infectious variants arise.
In early February, lab tests on the Pfizer vaccine found it may still provide substantial protection against the South African variant. The results, published in Nature, indicated that the B.1.135 variant did not dramatically undermine the vaccine’s efficacy.
But last week a new report on lab tests, also published in Nature, suggested that the B.1.351 variant is “markedly more resistant” to both Pfizer and Moderna vaccines.
Taylor says that while AstraZeneca and other manufacturers are already incorporating the South African mutation into their formulations, many countries struggle to control the rapid spread of different variants.
“The UK variant is currently the most abundant variant in many countries, and [the AstraZeneca vaccine] protection against the UK variant remains good,” he says.
“Australia must continue to administer vaccines that provide good protection against globally circulating strains of SARS-CoV-2,” adds Taylor. “The AstraZeneca vaccine provides protection from severe forms of COVID-19 and is effective against globally circulating strains that continue to threaten Australia.”
Related reading: South African concern
Dr Manuela Callari is a Sydney-based freelance science writer who specialises in health and medical stories.
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