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AstraZeneca Pauses Covid-19 Vaccine Trial After Illness in a U.K. Subject

The Wall Street Journal. logo The Wall Street Journal. 9/9/2020 Peter Loftus
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AstraZeneca PLC said Tuesday it paused clinical trials of an experimental Covid-19 vaccine after a participant in a U.K. study had an unexplained illness.

The company, which licensed the vaccine from developers at the University of Oxford, said the voluntary pause was a routine action that would allow an independent committee to review safety data.

The halt is a setback for the vaccine effort, which has long been touted as one of the world’s most advanced candidates. The shot had quickly progressed to late-stage studies in various countries, with AstraZeneca already signing contracts that could result in the delivery of initial doses this fall.

The pause affects a study that began last week in the U.S. aiming to enroll 30,000 people, with funding from federal agencies. The study is testing whether the vaccine reduces the rate of Covid-19 cases compared with unvaccinated study subjects. AstraZeneca and Oxford had started a large study of the vaccine in the U.K. in the spring.

The company is also testing the vaccine in studies in Brazil and South Africa.

AstraZeneca called the pause a “routine action which has to happen whenever there is a potentially unexplained illness in one of the trials, while it is investigated, ensuring we maintain the integrity of the trials.”

It added that it was taking steps to expedite the review of the event to minimize any potential impact on the trial timeline.

Oxford University issued a similar statement, saying that while illnesses will happen by chance in large trials, they must be reviewed independently.

Both the drug company and the university said they were committed to the safety of study participants and the highest standard of conduct in trials.

AstraZeneca was among a number of companies, including Moderna Inc. and Pfizer Inc., to publicly pledge this week to make the safety and well-being of vaccinated individuals the priority in the development of the first Covid-19 vaccines.

The study halt was reported earlier Tuesday by Stat.

Investors appeared largely unmoved by the news, with AstraZeneca’s shares falling less than 1% in London in morning trading Wednesday.

Analysts at Jefferies said temporary pauses were standard clinical trial practice, and that it wasn’t surprising that a serious adverse event triggered the study to be halted.

AstraZeneca has promised to provide more than two billion doses of its experimental vaccine and has struck deals to sell the shot to various countries including the U.S. and U.K. The British company is also working with partners to provide doses for low and middle-income countries.

Write to Peter Loftus at


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