COMMENT:

Yesterday, AstraZeneca pushed the pause button on its late-stage trials of a Covid-19 vaccine.

A clinical trial participant has experienced a serious health event and an investigation is underway to determine the cause. What does it mean?

With more than 200 Covid-19 vaccines now under development we are going to start seeing participants in the clinical trials have heath events.

Advertisement

These events may or may not be completely unrelated to the vaccine under study.

When you have what will ultimately be hundreds of thousands of people under observation in clinical trials, some will get sick, especially when you start recruiting older people into these studies.

When this happens sometimes the trial will need to be halted while the event is investigated, and a lot of questions answered.

Did the person receive the vaccine or a placebo? How long after the injection did this event occur? What sort of health event is this?

For example, is it heart attack? An infection? An injury? A seizure? Something else? Is this event biologically plausibly explained by receipt of the vaccine?

As the Covid-19 vaccine trials progress we are going to see periodic haltings of these trials.

This is actually the second time the Oxford/AstraZeneca vaccine trials have paused.

One reason for halting a trial is because a participant has had an adverse medical event.

Advertisement

We must accept the possibility that one, or some, of these new vaccines may have safety problems and fail to progress further.

We must also accept that if the event has been determined not caused by the vaccine the trial may resume. This is normal practice.

Who oversees the safety data on the trials?

Each clinical trial has a Data and Safety Monitoring Board (DSMB).

This is an independent group of people who have expertise in the disease, the drug, statistics, or other relevant fields.

While they will periodically review the study data for evidence of study-related adverse events, they can also make recommendations to the developer about continuing the study, modifying the study, or even terminating the study.

Advertisement

When a serious event occurs they are alerted and will convene urgently.

The data they review, and discussions are confidential.

In the case of Covid-19 vaccines, a large pool of safety-trained people have been recruited into a meta-DSMB.

This team can liaise across all the individual DSMBs across all of the different vaccine products.

This can help ensure the same level of rigour and standards are applied to all Covid-19 vaccines – at least those receiving support from CEPI, or the Coalition for Epidemic Preparedness Innovation.

About the vaccine

This vaccine was developed at Oxford University. Pharma giant AstraZeneca have partnered with Oxford to make it.

Advertisement

The vaccine is called a non-replicating viral vector vaccine and it uses an adenovirus that has had the gene for the SARS-CoV-2 spike protein inserted in to it.

When injected, the vaccinee's own cells will make the spike protein and the immune system generates a response.

There is some experience with viral vector vaccines in humans and so far there are no particular safety concerns identified associated with this particular viral vector construct (ChAdOx1).

According to the New York Times, the adverse event is a case of transverse myelitis - but this has not yet been confirmed by the company.

Transverse myelitis is an inflammatory condition that affects the spinal cord.

Biologically speaking many infections, such as the herpes and influenza viruses are known to cause this condition.

Advertisement

It has even been reported associated with Covid-19. Historically there have been rare cases of such immune mediated inflammatory disorders associated with vaccines, but a firm causal link has never been established.

This event does not affect other trials, particularly those using different vaccine platforms.
It also demonstrates that safety is being taken very seriously.

We need to be patient and let the trials run their course.

• Associate Professor Helen Petousis-Harris is a University of Auckland vaccinologist. The full version of this editorial, republished with permission, can be viewed on SciBlogs.co.nz.