Why the pause in the Oxford University coronavirus vaccine trial is actually good news

Tom Clarke

Former Science Editor

Just when you thought 2020 couldn’t get any worse. Cases are climbing again, restrictions are tightening back up, and now they’ve pulled the emergency breaks on the most promising and well-advanced COVID-19 vaccine trial in the world. 

But the pause the Oxford trial is actually good news. The only thing worse than no vaccine for COVID-19 is a bad vaccine.

And one of the biggest worries about the the world racing to develop a completely new vaccine against a completely new disease is that a mistakes could have gone unnoticed. 

Concerns made more real by signs of a bizarre jab-in-the-arms-race, led by the likes Vladimir Putin and Donald Trump promising to fast-track vaccines being tested in their countries.

While we’ve go no information yet on why the trial was paused overnight, the one thing it does show is that the safety systems in place to prevent any adverse reactions to a new vaccine are working.

Vaccines aren’t like ordinary drugs, they’re designed to be given to as many people as possible irrespective of age, ethnicity or health status.

They get safety-tested in small numbers of people first so typically any adverse events not spotted at this stage are by definition rare. That’s why, in order for them to be considered safe for the population at large they HAVE to be tested in large numbers of people.

The adverse event in this case could have nothing at all to do with the vaccine. If anyone in the trial becomes ill after receiving the vaccine in a well-conducted trial it is automatically halted.

The only thing worse than no vaccine is one that does not work well. Credit: AP

In this phase 2/3 stage of the trial, the vaccine was being rolled out to 30,000 people worldwide including those over 70. The likelihood of someone, somewhere getting ill after receiving the jab, even if it was completely unrelated to the jab, is pretty high.

But it is, of course, possible that the vaccine itself causes an adverse reaction either at random, or in a certain type of person.

COVID-19 vaccine researchers are particularly concerned about a potential problem called ADE or antibody-dependent enhancement.

This worrying phenomenon was first seen in a 1960s trial of a vaccine against respiratory syncytial virus (RSV) in children; 80% of the children in the trial ended up in hospital and two died.

The HPV vaccine has saved thousands of lives. Credit: PA

It turns out the antibodies their bodies made actually helped RSV invade their cells.

A similar problem was seen in some animals tested with experimental coronavirus vaccines. 

For various technical reasons, the Oxford vaccine is unlikely to cause this reaction. But if it did, even in a very small number of people, that’s precisely why clinical trials are needed.

And why, if there’s even a hint of a problem, they have to stop, before moving cautiously forward again once the coast is clear.