The University of Kansas Medical Center and Children’s Mercy Hospital have halted a clinical trial of a COVID-19 vaccine after a participant in the United Kingdom developed an adverse reaction.
Pharmaceutical company AstraZeneca, which developed the vaccine along with the University of Oxford, said on Tuesday that it had put Phase 3 testing of the vaccine on hold while it conducts a safety review of the data.
KU Med Center and Children’s Mercy are leading the local effort to test the vaccine, known as AZD122. The Phase 3 trial in the U.S. began last month and involves 62 sites across the country.
During Phase 3 of a clinical trial, the vaccine is given to thousands of volunteers to see how many become infected compared with volunteers who receive a placebo.
The halt of the trial was first reported by STAT News, which said it was unclear how severe and rare the adverse reaction was.
The New York Times reported that a source familiar with the situation said a volunteer in the U.K. trial had been found to have transverse myelitis, an inflammatory syndrome affecting the spinal cord that is often triggered by viral infections. Whether it was linked to the vaccine was unclear, the Times said.
It’s not uncommon for clinical trials to be paused, and it’s not clear how long AstraZeneca’s hold will remain in effect.
Children’s Mercy referred inquiries to AstraZeneca, which said in a statement that all trials had been voluntarily paused “to allow an independent committee to review the safety data of a single event of an unexplained illness” that occurred in the U.K. Phase 3 trial.
“In large clinical trials, illnesses will happen by chance and must be independently reviewed,” it said. “AstraZeneca is working to expedite the review of the single event to minimize any potential impact on the trial timeline. We are committed to the safety of our participants and the highest standards of conduct in our trials.”
AZD1222 uses a genetically engineered virus taken from chimpanzees that carries a gene for one protein in the coronavirus, which causes COVID-19. The virus is inserted into patients’ cells, causing them to manufacture that protein, which in turn triggers an immune response.
AstraZeneca hopes to enroll 30,000 people in its Phase 3 trials in the United States. The KU/Children’s Mercy trial was looking to recruit 1,500 participants.
AstraZeneca halted the trial on the same day it and eight other drug companies pledged that they would not move forward with COVID-19 vaccines before thoroughly vetting them for safety and efficacy.