Why has the Oxford/AstraZeneca vaccine trial been paused?

One of the volunteers in the UK has become ill and it is crucial that the researchers find out whether this could be related to the vaccine. This is not uncommon in vaccine trials – and in fact it is said to be the second time it has happened with this vaccine . Very large trials are essential to pick up any rare side-effects. Something that affects one in 10,000 people, for instance, will probably not be detected in the early trials of just a few thousand.

Do we know what the illness is?

It is said to be transverse myelitis, although AstraZeneca has not confirmed that. That is inflammation of the sheath containing the nerves of the spinal cord. It can be treated by steroids to reduce the inflammation but the condition can be permanent.

Transverse myelitis has been associated with vaccination before, but only very rarely. A study in 2018 looking at more than 30 years of data from the US vaccine adverse event reporting system found 119 cases in 29 men and 90 women, which is a tiny number compared with the numbers vaccinated. However, they were clustered in the first weeks after vaccination, which made the researchers think it could be a rare vaccination-related event. Nearly half the cases followed a hepatitis B vaccination.

How will this affect the trial?

Investigators will be examining the details of the illness and the person who contracted it to find out if there is a link. They will also look at the dose of vaccine they received, their state of general health and so on. They will hope this event can be explained and is not a risk to others. If so, the trial will soon resume. Researchers in other vaccine trials – there are nine now in phase 3, which is the last stage – will be looking to ensure they are not seeing a similar issue.

Is this a consequence of the rush for a vaccine?

Probably not. Although the trials have been set up in record time, there has been great emphasis on safety and, in the current spotlight, it is unlikely researchers or manufacturers would want to cut corners. This could have happened if the trials had spanned several years instead of several months.

Will there be other repercussions?

Given the huge amount of attention being paid to Covid-19 vaccine trials, it is possible the pause will dent public confidence. In previous vaccine trials, we would not have noticed pauses of this sort, because the outcome was less immediately critical to global public health. There are anti-vax movements talking about the supposed dangers of vaccination and there are some who argue that it is better for healthy people to catch Covid-19 and recover from it. However, that is by no means necessarily the safer route. As we know, in rare cases, young and apparently healthy people can also become severely ill and there are long-term effects of the virus.