AstraZeneca announced that the clinical trial program evaluating its investigational vaccine for coronavirus disease 2019 (COVID-19), AZD1222, has been temporarily paused due to an unexplained illness that occurred in a phase 3 trial in the UK.

AZD1222 utilizes a replication-deficient chimpanzee viral vector (weakened adenovirus) to deliver a severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) protein to induce a protective immune response. Interim results from the phase 1/2 COV001 trial showed that AZD1222 elicited strong immune responses against SARS-CoV-2 in healthy adults. With regard to safety, transient local and systemic reactions were reported to be common; these included temporary injection site pain and tenderness, pain, feverishness, chills, muscle ache, headache, and malaise.

In a statement, the Company noted that the actions being taken are considered “routine” when a potentially unexplained illness is reported in a clinical trial. Commenting on the issue, Pascal Soriot, Chief Executive Officer, said: “We will be guided by [a committee of independent experts] as to when the trials could restart, so that we can continue our work at the earliest opportunity to provide this vaccine broadly, equitably and at no profit during this pandemic.”

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A US phase 3 trial investigating the vaccine candidate was initiated earlier this month and is expected to enroll approximately 30,000 adult volunteers. According to the Food and Drug Administration, no new participants can be recruited to a study that has been placed on clinical hold.

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Statement on AstraZeneca Oxford SARS-CoV-2 vaccine, AZD1222, COVID-19 vaccine trials temporary pause. Accessed September 9, 2020.