Photo: Lisa Maree Williams/Getty Images

AstraZeneca's COVID-19 vaccine trial has been put on pause after researchers suspected an adverse reaction in a participant in the United Kingdom, a spokesperson for the company told Stat News.

Why it matters: There are presently nine vaccine candidates in Phase 3 trials. AstraZeneca’s is one of the most promising candidates, and is the first known Phase 3 vaccine trial to be halted.

Of note: It is unclear what the unfavorable reaction was and when it occurred, but the participant is expected to recover. It's also not known who paused the study, how severe or rare the reaction may be and how long the hiatus could last.

  • A variety of responses may be flagged for possible adverse reactions, including hospitalization, life-threatening illness and death.

What they're saying: The halt is “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," AstraZeneca said in a statement per Stat News.

"In large trials illnesses will happen by chance but must be independently reviewed to check this carefully. We are working to expedite the review of the single event to minimize any potential impact on the trial timeline."

The big picture: AstraZeneca started its Phase 3 trial in the U.S. in late August. The process is taking place across 62 sites throughout the country.

  • Phase 2 and 3 trials previously began in the U.K., Brazil and South Africa.

Go deeper

Updated 3 hours ago - Health

World coronavirus updates

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Data: The Center for Systems Science and Engineering at Johns Hopkins; Map: Axios Visuals

The number of deaths from COVID-19 surpassed 980,000 worldwide on Thursday.

By the numbers: Globally, more than 32 million million people have tested positive for the novel coronavirus, Johns Hopkins data shows.

Coronavirus cases rise in 22 states

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Data: The COVID Tracking Project, state health departments; Note: Texas added a backlog of cases on Sept. 22, removing that from the 7-day average Texas' cases increased 28.3%; Map: Andrew Witherspoon, Sara Wise/Axios

The coronavirus is surging once again across the U.S., with cases rising in 22 states over the past week.

The big picture: There isn't one big event or sudden occurrence that explains this increase. We simply have never done a very good job containing the virus, despite losing 200,000 lives in just the past six months, and this is what that persistent failure looks like.

23 hours ago - World

Trudeau: Canada's coronavirus second wave has begun

Prime Minister Justin Trudeau during an August news conference on Parliament Hill in Ottawa, Canada. Photo: Dave Chan/AFP via Getty Images

Prime Minister Justin Trudeau said during a televised address on the coronavirus pandemic Wednesday that for Canada's four biggest provinces, "the second wave isn’t just starting, it's already under way."

Driving the news: Daily case numbers have gone from roughly 300 cases a day in mid-August to 1,248 by Tuesday, with most outbreaks in British Columbia, Alberta, Ontario and Quebec, CBC notes. "We're on the brink of a fall that could be much worse than the spring," Trudeau said. "It's all too likely we won't be gathering for Thanksgiving, but we still have a shot at Christmas." Over 147,700 Canadians have tested positive for COVID-19.

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