Oxford coronavirus vaccine trial on hold after adverse reaction in participant

A phase 3 clinical trial of a promising coronavirus vaccine candidate, developed by the University of Oxford and biopharmaceutical giant AstraZeneca, has been put on hold due to a "suspected serious adverse reaction" in one of the study's participants, according to a report by STAT news.

The COVID-19 vaccine, known as AZD1222, is considered one of a handful of promising coronavirus vaccines and had recently begun clinical testing in the US and the UK. A spokesperson told STAT the hold is "a routine action which has to happen whenever there is a potentially unexplained illness in one of the trials." A review process triggered the pause, according to the spokesperson.

Clinical trials are often placed on pause to investigate the nature of any adverse events. This is exactly how they are supposed to work and why researchers perform stringent phase 3 trials in the first place. They are designed to ensure the highest level of safety before a vaccine is rolled out to the public.

"This, while disappointing, should reassure us that the proper processes and safety precautions are being followed, despite the urgency of this pandemic," said Hassan Vally, an infectious diseases epidemiologist at La Trobe University. "The reality is that these reactions do occur and they need to be examined closely." 

The nature of the adverse reaction is currently unclear, but it is now being investigated and believed to have been in a participant from the UK. They are expected to recover. It's also unclear if the adverse reaction is linked to the vaccine. "One person in 50,000 having an unexplained illness during a human trial has a significant chance of this being unrelated to the vaccination," says Madgalena Plebanski, professor of immunology at RMIT University, Melbourne, Australia. "No need to panic yet."

Vally suggests more information on the event is required. Other researchers suggest it may not be just minor side effects.

"Would be good to know what the problem was," said Katherine Seley-Radtke, a medicinal chemist studying antivirals at the University of Maryland, "but the fact it has put a hold on things sort of speaks for itself." 

STAT reports the event is "having an impact" on other vaccine trials conducted by AstraZeneca and researchers in other trials are reviewing data looking for similar adverse reactions. 

AstraZeneca did not immediately respond to a request for comment.

On Aug. 31, the US National Institutes of Health announced approximately 30,000 adult volunteers across the US would be enrolled in the phase 3 trial, which is designed to evaluate the vaccine in a diverse population and monitor for adverse events. The trial is part of Operation Warp Speed, a collaborative effort aimed at accelerating the development of COVID-19 treatments in the US. 

Last week, the Australian government announced it would be ordering 33.8 million doses of the vaccine and says 3.8 million of those doses would be delivered in January and February 2021 if the vaccine is successful.

The vaccine itself is a "viral vector" vaccine and uses a weakened cold virus to present a small piece of COVID-19 genetic data to human cells. It works to mimic a coronavirus infection and is designed to stimulate an immune response by exposing cells to the coronavirus "spike protein." In results from phase 1 and 2 trials, published in medical journal The Lancet in July, the Oxford vaccine was shown to stimulate white blood cells and antibodies -- which can attack or neutralize a virus. The researchers note mild and moderate reactions were common, but many were reduced by use of paracetamol and no serious adverse events were reported.

This story is developing.