The AstraZeneca-Oxford vaccine is not effective against moderate infections of the South Africa variant of the coronavirus, according to a new study that complicates the strategy for curbing the pandemic through immunization.
A new study in the New England Journal of Medicine found that the vaccine had an efficacy of only 10.4% against mild-to-moderate cases of COVID-19 involving the South Africa strain, also known as B.1.351. Yet, there were no severe cases or hospitalizations among the participants.
Authorities in the United States have targeted vaccine efficacy at 50%.
Further muddying the analysis of the new study is that it is not clear what the results mean for groups vulnerable to COVID-19. An earlier study in South Africa yielded similar results, of only 10% efficacy. That study was criticized for having a small sample size of only 2,000 and for focusing heavily on young people. The average age of participants was 31.
The NEJM study has similar shortcomings. Its sample size was about 2,000, and no one over age 65 was examined, leading to a median age in the study of 30. Thus far, it is not clear how the AstraZeneca vaccine performs against the South Africa variant in people over age 65, the population most likely to get severe COVID-19 and be hospitalized.
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Other vaccines have also shown lower rates of efficacy against the South Africa variant. The Novavax vaccine has an efficacy of 49%, while the Johnson & Johnson vaccine had an efficacy of 57%. Research from Pfizer-BioNTech showed that its vaccine’s neutralization of the South Africa variant “was robust but lower” than against the other variants.
Thus far, the dominant variant in the U.S. appears to be the United Kingdom one. The Centers for Disease Control and Prevention reports 4,686 cases identified in 50 states. By contrast, 142 cases of the South Africa variant have been identified in only 25 states. That may be due to the fact that the South Africa strain’s ability to bind to enzymes is weaker than the U.K. strain, according to recent research from the Netherlands.
Experts say that it may not be difficult to modify vaccines to combat new variants. Moderna is already working on a new vaccine designed to match the South Africa variant.
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It has been a difficult few weeks for AstraZeneca, as multiple European countries have suspended their use of the vaccine amid reports that it caused blood clots among recipients. The European Medicines Agency has said that the rate of blood clots among those taking the vaccine is no higher than in the public at large. The EMA is examining the issue and is expected to make a ruling Thursday.
