2nd big COVID-19 vaccine trial paused because of possible serious side-effect. Here's what that means

Anotherfront-running team in the race to develop a COVID-19 vaccine has put alate-stage trial on hold after a reported "unexplained illness" in one of the trial volunteers. Here's a look at the two pauses and what they meanfor the quick development of a COVID-19 vaccine.

What kind of vaccine trials got put on hold?

Both pauses includedPhase 3 clinical trials for the same classof vaccine, non-replicating viral vector vaccines.

Phase 3 isthe largest type of clinical trial, requiring thousands of volunteers, and is the last of three stages of human testing before a vaccine can be approved for use. Its main goals are to:

• Test the efficacy of the vaccine at preventing the disease compared witha placebo

• Get a better idea of possible side-effects and how often they happen, including rare side-effects that might not show up in smaller trials.

The two vaccine makers that paused the trials are:

• TheUniversity of Oxford and pharmaceutical company AstraZeneca, which announced their pause on Sept. 8.The company is running Phase 3 trials involving thousands of people in the United Kingdom and smaller numbers of people in Brazil and South Africa. It is also recruiting 30,000 people in the United States for its largest study. The trials have since resumed in the U.K., Brazil and South Africa, but regulators have not yet approved them to resumein the U.S.
• Janssen Pharmaceutical Companies, a subsidiary of Johnson & Johnson, which announced their pause on Oct. 12. The companyis running both earlyand late-stage clinical trials and did not say which the volunteer participated in. However, Johnson & Johnson said it was pausing all its COVID-19 vaccine trials. That includes a Phase 3 trialthat started in late September and aimedto enroll 60,000 volunteers in Argentina, Brazil, Chile, Colombia, Mexico, Peru, South Africa and the U.S.

Canada has deals to purchase tens of millions of doses of vaccine from each of the two companies if they make it through clinical trials and are approved.

Why werethe trials suspended?

Both companies blamed an "unexplained illness" in one of the volunteers. That would have triggered a"standard review process," intended to ensure safety when that happens. The pause allows the incident tobe investigated by independent reviewers not involved in the trial.

What kind of illness was it?

Johnson & Johnson declined to reveal any more details about the illness, citing the participant's privacy.

In AstraZeneca's case, the company acknowledgedthat the patient hadneurologicalsymptoms associated with aspinal inflammatory disordercalled transverse myelitis.

That involveslocalized inflammation of the spinal cord, which can cause symptoms such as weakness, loss of sensation or even paralysis of the arms and legs. It can be caused by autoimmune diseases, viral, bacterial or fungal infections or parasites, but it has also been reported as potentially a rare side-effect of vaccinations for diseases such as hepatitis B,influenza or measles-mumps-rubella.

The diagnosis was later confirmed by an internal report on the incident, CNN reported.

However, researchers who have studied transverse myelitis note that it's difficult to confirm or exclude the link between the disease and vaccination, since it can occur coincidentally as a result of other causes after vaccination.

The U.S.-based Mayo Clinic saidthat the association so far is not strong enough to warrant limiting any vaccine.

WATCH|Pausing COVID-19 vaccine trial is 'standard conduct,' says expert:

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Johnson & Johnson pausing their clinical COVID-19 vaccine trial is not uncommon in the scientific process with safety being a top concern, says infectious disease specialist Dr. Isaac Bogoch.

What is the goal of the review?

It will try to determine whether the illness was related to the vaccine.

Because trials like this are typically double-blinded, the researchers don't know whether a given volunteer received the vaccine or a placebo. That's one of the reasons why the review needs to be conducted by an independent committee that is not doing other analyses in the study.

Even if the volunteer received the vaccine, the timing of the illness could still be coincidental and unrelated to the vaccine.

Dr. Sumon Chakrabarti, an infectious disease specialist at Trillium Health Partners in Toronto, told CBC News Network that if the patient does have transverse myelitis, he or she will likely be tested for different types of infections to see if a cause can be determined.

"I've seen many of these cases myself, and we often come up with viral causes," he said.

If that happens, the review may be able to rule out the vaccine as the cause and allow the trial to resume.

WATCH | Dr. Sumon Chakrabarti explains pauses in vaccine trials:

Oxford University pauses COVID-19 vaccine trial

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Dr. Sumon Chakrabarti, infectious diseases specialist at Trillium Health Partners, said safety is paramount in vaccine clinical trials, and temporary suspensions are not unusual to evaluate any unexplained illness in a participant.

How often do pauses like this happen?

On the one hand, they're not triggered by "mild" side-effects, and there haven't been any publicizedforany COVID-19 vaccine trials so far, despite the large number underway. However, following the September pause, AstraZeneca disclosed that it had briefly paused a COVID-19 vaccine trial in July after a study volunteer wasfound to have multiple sclerosis. An independent review panel concluded the illness was not related to the vaccine.

Dr. Samir Gupta, associate professor of medicine at the University of Toronto, said that "it's not a routine thing to stop a massive trial mid-course like this."

However, AstraZeneca CEO Pascal Soriot said Thursday that such pauses are "very common actually."

"Many experts will tell you this," he said. "The difference with other vaccine trials is that the whole world is not watching them of course so they stop, they study and they restart."

Such an event is not unexpected, given the size of the trial, said Dr. Michael Gardam, an infectious disease specialist at Women's College Hospital in Toronto.

"I would argue for probably every vaccine that's ever come to market, there's been an event like this," Gardam said.

"When you're giving vaccine to tens of thousands of people, something's going to happen to one of them. And chances are it's happenstance ... it's not linked to the vaccine. But each time, you have to investigate it."

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Some potential COVID-19 vaccines are already in the third stage of clinical trials. Its taken a lot of effort and money to squeeze a process that can normally take five years into about 10 months and still be done safely.

Will the pause slow down development of a vaccine?

"Not necessarily, it dependson what they find when they do the investigation," British Health Secretary Matt Hancock said on Wednesday.

Gardamsaid he doesn't think it will cause a significant delay.

Investigators will try to figure out "a reasonable explanation" for the cause of the illness, Gardam said, which may take some time.

A pause occurredduring the Phase 1 trial of a Canadian-made Ebola vaccine in 2014 after several volunteers reported joint pain. An investigation found that the side-effect was likely caused by the vaccine, and the study resumed three weeks later with a lower dose.

In this case, Gardamsaid he thinks it will be hard to draw any conclusion based on one illnessand that the University of Oxford researchers will be able to "quite quickly get back up and running again."

However, they will need to collect more data to see if others show similar illnesses. If that happens, he said, "then that's a completely different story."

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An infectious disease specialist answers viewer questions about a COVID-19 vaccine including what stage vaccine development is in and when the public could expect one to be ready.

How worried should we be about thesepauses?

If itturns out that this is a potential adverse effect of this vaccine, "that would obviously be a substantial showstopper for this vaccine," said Dr. Andrew Morris, an infectious disease specialist at Sinai Health, the University Health Network and the University of Toronto, following the University of Oxford/AstraZeneca pause.

He's concerned there wouldn't be access to the vaccine, which is in advanced stages of development. It's also one that many countries are pinning their hopes on, with substantial investment from and billions of dosesreserved bygovernments around the world and by the COVAX Facility, which aims to provide access to 172 countries, including many in the developing world. The company says it is close to having the capacity to producethree billion dosesaround the world to prevent governments from restricting distribution.

Morris said he's also concerned that the media coverage will discourage people from enrolling in vaccine studies or increase anti-vaccination hype.

"Any step back is really a setback for all of us," he said.

But at the same time, researchers such as Gardam say in some ways, the pause should ease people's concerns, as it shows that the system is working and highlights the importance of Phase 3 clinical trials to ensure the safety of vaccines.

"This in and of itself isn't a big deal," he said. "This is what is supposed to happen.... This gives me some comfort.

"The fact that this has been stopped appropriately, it'll be investigated. We'll learn about itand then presumably the trial will start up again. That's exactly what's supposed to happen."