The Phase 3 trial of the Covid-19 vaccine developed by the University of Oxford and AstraZeneca has been paused, reportedly due to a suspected ‘serious adverse reaction’ by one of the participants in the UK.
AstraZeneca only said that its “standard review process triggered a pause to vaccination to allow review of safety data,” according to a statement by a company spokesperson on Tuesday. It was unclear whether the hold was self-imposed or ordered by a regulator, what the adverse reaction may have been, or when it might have happened.
BREAKING: AstraZeneca’s #Covid19 vaccine trials have been paused as the company investigates a serious adverse event the occurred in the UK. Not clear if the unexplained illness is linked to the vaccine, or what it was. https://t.co/wGqvvXIBTD
Anonymous sources told the news site Stat that the participant is “expected to recover,” but the information could not be independently confirmed.
AstraZeneca’s vaccine is the first Covid-19 trial put on hold upon reaching Phase 3, according to Stat. The study on phases one and two, published in July by the medical journal Lancet, noted that about 60 percent of the participants had developed side effects – fever, headaches, muscle pain, and injection site reactions, mainly – that were described as “mild or moderate” and subsided during the course of the trials.
It is unclear what effect the UK pause will have on the plans for Phase 3 testing in the US, which is supposed to enroll some 30,000 participants at 80 locations, according to the National Institutes of Health.
AstraZeneca’s vaccine client, AZD1222, uses an adenovirus that shares a gene with SARS-Cov-2, the coronavirus that causes Covid-19. The adenovirus platform is considered experimental in the West, but has served as the basis for Russia’s own vaccine for the coronavirus, dubbed Sputnik-V, which was rolled out to the public this week.
A peer-reviewed study of the early stages of Sputnik-V testing, published by The Lancet last week, suggested the Russian vaccine was both effective and safe. The journal noted that longer-term trials, including a placebo comparison, would be required to establish its bona fides beyond a reasonable doubt.
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