AstraZeneca’s COVID-19 vaccine shows overall efficacy of 70% with two doses
AstraZeneca and Oxford University’s COVID-19 vaccine demonstrated an overall efficacy of 70% after two doses, according to interim data from four trials published in The Lancet.
“Here, we have shown for the first time that a viral vector vaccine, ChAdOx1 nCoV-19, is efficacious and could contribute to control of the disease in this pandemic,” Merryn Voysey, DPhil, lead statistician with the Oxford Vaccine Group, and colleagues wrote.
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An interim analysis of the vaccine from the United Kingdom and Brazil previously showed an average efficacy of 70% and no safety concerns.
In the latest study, Voysey and colleagues analyzed data from trials in the U.K., Brazil and South Africa. They included 11,636 patients for the primary efficacy analysis. Patients were randomly assigned to receive either the ChAdOx1 nCoV-19 vaccine or a control vaccine containing saline or a meningococcal group A, C, W and Y vaccine. Participants who received the ChAdOx1 vaccine were given two doses, but a subset of participants in the U.K. were given a half dose first — which was due to a manufacturing error, media outlets reported — followed by standard dose as their second dose.
According to the researchers, the efficacy of ChAdOx1 was 62.1% (95% CI, 41-75.7) among those who were given two standard doses, and 90% (95% CI, 67.4-97) among participants who were given a half dose followed by a standard dose.
“Until widespread immunity halts the spread of SARS-CoV-2, physical distancing measures and novel therapies are needed to control COVID-19,” the researchers wrote. “In the meantime, an efficacious vaccine has the potential to have a major impact on the pandemic if used in populations at risk of severe disease.”
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That a half dose followed by a full dose is more effective compared with two full doses is an active area of research and may have to do with the viral vector used in this vaccine. Perhaps a full dose confers too much immune reaction to the vector, which blunts response to the target protein.
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