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AstraZeneca, the pharmaceutical company developing a large Phase 3 trial of a COVID-19 vaccine, said it is putting the trial on hold Tuesday just one week after Michigan Medicine announced plans to partner with the company.

The hold was due to a suspected serious adverse reaction in a participant in the United Kingdom. A spokesperson for the company said in a statement to STAT that their “standard review process triggered a pause to vaccination to allow review of safety data.”

The AstraZeneca trial is expected to last about two years and aims to test a total of 30,000 participants at 80 sites across the country. The University is one of dozens of sites across the US participating in the trial.

Clinical holds often involve pausing the recruitment of new participants and stopping dosing for existing participants, unless it is in the interest of the participants’ safety to continue doing so.

It is not yet clear what steps are being taken at the study sites following the hold. Mary Masson, Michigan Medicine’s director of public relations, declined to answer questions about the status of the trial at the University, referring The Daily to AstraZeneca for a comment. AstraZeneca did not respond in time for publication.

The AstraZeneca trial — known officially as AZD1222 — uses an adenovirus that carries a gene for one of the proteins in the SARS-CoV-2, the virus that causes COVID-19. The adenovirus is designed to induce a protective response by the immune systems against SARS-2.

According to a Phase 1/2 study published in July, about 60 percent of 1,000 participants given the vaccine experienced mild to moderate side effects such as headaches, muscle pain or fever. All of the reported side effects subsided during the course of the study.

While it is unclear how severe and rare the adverse reaction is, it could impact how quickly efficacy data will be available from the U.K. trial. This data, which demonstrates whether or not the vaccine is effective over placebos or other interventions, is crucial in seeking authorization for emergency use from the Food and Drug Administration.

In a statement announcing Michigan Medicine’s partnership with AstraZeneca to conduct the trial, Marschall Runge, the University of Michigan’s executive vice president for medical affairs and Michigan Medicine CEO, said a vaccine will be critical in stopping the spread of the coronavirus once one is developed.

“The importance of a safe and effective vaccine against COVID-19 cannot be overstated,” Runge said. “The AstraZeneca Phase III trial will bring answers as to the effectiveness of this vaccine. At the end of the day, this kind of rigorous clinical trial with the commitment of Michigan Medicine and other study sites to safety will be a key step in realizing a vaccine that will save lives when one is developed.” 

Daily Staff Reporter Iulia Dobrin can be reached at

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