- South Africa has stopped the planned rollout of a vaccine from AstraZeneca and the University of Oxford after the shot provided "minimal protection" against mild to moderate COVID-19 caused by a coronavirus variant that originated within the country and has since spread elsewhere.
- The disappointing preliminary results, from a trial testing the shot in roughly 2,000 participants in South Africa, indicate the vaccine was only 22% effective at reducing mild to moderate disease. But the small size of the trial and other study limitations make the findings difficult to interpret. And it's unknown whether the shot still protects immunized patients from severe disease or hospitalization from COVID-19 caused by the variant, known as B.1.351.
- Nonetheless, the results are the latest evidence that the B.1.351 variant may reduce the potency of multiple coronavirus vaccines, though it's unclear to what degree. South Africa will reportedly now use other vaccines from Johnson & Johnson and Pfizer to start its immunization campaign, and Oxford researchers are working on an updated version of their shot.
The world has bet more on the AstraZeneca and Oxford vaccine than any other. AstraZeneca expects to make more than 3 billion doses this year, the most of any vaccine maker, and a large chunk of those have been pre-ordered by several countries. The shot can also be stored and distributed in refrigerator conditions, making it a crucial part of the global immunization campaign.
Yet several setbacks and confusing clinical results have slowed the vaccine's progress and dampened enthusiasm regarding its potential. Though the shot appears to prevent COVID-19 caused by the original strain of SARS-CoV-2, researchers still aren't sure what the best dosing regimen is or how effective it is in the elderly. The vaccine also may slow transmission of the virus, though again, it's unclear to what degree.
A large U.S. study, expected to read out in February or March, could finally clear up the confusion. But in the meantime, the fresh data presented Sunday raise new questions about its utility.
The study tested whether two doses of the vaccine or placebo could prevent mild to moderate COVID-19 14 days or more after the second shot. A preliminary analysis conducted after 42 cases, showed that 23 occurred in 717 placebo recipients, compared to 19 of 750 who got the vaccine — a roughly 22% reduction and well short of the goals established by regulators across the globe.
Against the B.1.351 variant specifically, the difference was even smaller — 20 cases for placebo participants and 19 for those who were immunized.
By comparison, the shot was found 66.7% effective at preventing COVID-19 in pooled results from multiple late-stage studies in the U.K., Brazil and South Africa.
The new data, which come from Oxford and the Wits Vaccines and Infectious Disease Analytics Research Unit in South Africa, do come with important caveats. For example, the results were based on a small number of infections, and may not be indicative of what would be seen in a larger study. They haven't been peer reviewed, either.
They also include confidence intervals — a statistical measure to indicate uncertainty around an estimate — with a very wide range, from -50% to 60%. And researchers enrolled participants who were a median of 31 years old, a population less likely to suffer the worst health outcomes from COVID-19, meaning they only assessed whether the shot could prevent mild to moderate disease, not severe illness and hospitalization.
Still, the results are fueling concerns that the continued spread of the coronavirus is leading to mutations that could limit the effectiveness of the current crop of vaccines.
Promising shots from Novavax and Johnson & Johnson have already shown they're less potent against the B.1.351 variant, which possesses a significant mutation to the "spike" protein many vaccines target. Yet, those two vaccines were still very effective at preventing severe COVID-19, hospitalization or death from infections caused by the variant, making them useful even if they're not as effective against mild disease. AstraZeneca's shot, which works similarly to J&J's, may as well.
For now, the challenges posed by B.1.351 have upped the urgency to develop either additional booster shots or updated vaccines tailored to emerging variants. The Food and Drug Administration is reportedly discussing a speedy regulatory framework for updated vaccines that is similar to the strategy used to develop yearly flu shots. And both Moderna and Novavax are working on newer vaccines that should be ready for testing later this year.
Oxford researchers have similar plans to develop a second-generation shot.
"We are working with AstraZeneca to optimize the pipeline required for a strain change should one become necessary," said Oxford professor of vaccinology Sarah Gilbert, in a statement. "This is the same issue that is faced by all of the vaccine developers, and we will continue to monitor the emergence of new variants that arise in readiness for a future strain change."