AstraZeneca slides after its coronavirus vaccine trial is put on hold due to suspected adverse reaction

• AstraZeneca shares fell on Wednesday, following a 6% drop on Tuesday, after the pharmaceutical company paused its COVID-19 vaccine trial following a suspected severe adverse reaction.
• Shares in the drugs company, a leader in the race for a vaccine, were down by around 1% on London’s FTSE 100 index in mid-morning trading on Wednesday.
• Pausing the phase-three study is a “routine action which has to happen whenever there is a potentially unexplained illness in one of the trials,” the company said in a statement to CNBC.

AstraZeneca shares fell on Wednesday, extending a 6% fall on Tuesday, after the pharmaceutical company halted its coronavirus vaccine trial following a suspected severe adverse reaction from a participant.

Shares in the company, a front-runner in the race for a coronavirus vaccine, were down by around 1% on London's FTSE 100 index in mid-morning trading on Wednesday. AstraZeneca's US-listed shares fell by as much as 6% during after-hours trading on Tuesday.

AstraZeneca is developing a vaccine with the University of Oxford. Pausing the phase-three study — the final phase before potential approval — is a "routine action which has to happen whenever there is a potentially unexplained illness in one of the trials," the British company said in a statement to CNBC.

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Illnesses in large trials are expected, but each one must be reviewed carefully, it added. AstraZeneca also said it was "working to expedite the review of the single event to minimize any potential impact on the trial timeline."

The suspected serious adverse reaction was first reported by STAT. The details of the illness were not disclosed but the participant is expected to recover, according to a person familiar with the situation who spoke to STAT.

The World Health Organization has described the AstraZeneca vaccine as one of the leading and advanced contenders in the world to fight against COVID-19.

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