Dr. Stuart Weiss, FACEP, FAAP, CBCP

September 8, 2020

AstraZeneca Halts vaccine trial

Reported in the New York Times and STAT News

Astrazeneca, one of three companies in the US in late stage phase three trials has paused its global trials of its AZD1222 CoViD-19 vaccine because of a serious and unexpected adverse reaction in a British volunteer.

The vaccine trial's halt will allow the company to conduct a safety review of a condition called transverse myelitis which is an inflammatory condition affecting the spinal cord. In large scale trials, these unusual reactions sometimes occur and must be investigated. This is the reason that phase three large scale trials are important. It helps to bring out rare and unusual effects of a vaccine. It is also possible that this person developed this condition independent of the trial so this must be fully investigated. 

The Astrazeneca vaccine relies on a chimpanzee adenovirus that has been modified to carry SARS-CoV-2 genes into human cells. The chimp adenovirus is thought to be harmless in humans and the coronavirus components are thought to incite an immune response should a person come into contact with actual coronavirus in the future. However, sometimes Adenoviruses incite their own immune responses which can harm patients and this must be investigated. 

The company is working to investigate this and hopes to avoid any impact on the trial timeline.