The recent (possible) safety signal-prompted hiccup in AstraZeneca’s (NYSE:AZN) large-scale pivotal study of COVID-19 vaccine candidate AZD1222 exemplifies the risky nature of these types of trials, especially the ones involving vaccines against SARS-CoV-2 infection considering the profound global need and intense investor scrutiny. Every unexpected event, no matter how insignificant, will be guaranteed a full vetting in this environment.

On September 8, shares dropped over 8% after hours (a shining example of off-hours volatility) in the U.S. in reaction to the news that the company voluntarily stopped the trial after a UK patient fell ill after inoculation, an appropriate and expected action to a commonly encountered event, especially in a study involving 30K people. Investors apparently agreed. Shares in the U.S. ended the day up 2% from the close of $53.58 on Friday, September 4. Shares in London were up 0.8% from the day before.

The next day, reports came out that the participant experienced serious neurological symptoms, later reported as transverse myelitis, an inflammatory condition of the spinal cord, quickly disabused by the company, explaining that no final diagnosis had been made since some test results were pending.

Yesterday, AZN chief Pascal Soriot reiterated that he was unsure on the specific length of the study pause but the company still plans to have a dataset to support a regulatory filing and the vaccine ready by year-end.

Even if the independent safety committee determines that the patient’s condition was caused by the vaccine, the study will resume. In these cases, the study sponsor typically updates the disclosure documents and investigator (trial site) guidelines to account for the event.


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