If you’ve been following recent COVID-19 news, then you may have heard that one of the COVID-19 vaccine studies was paused last week in order to review an unexpected illness in one of the participants. While we all want the COVID-19 pandemic to end as soon as possible, I believe this pause is a very good sign that the COVID-19 vaccine researchers are behaving responsibly and with the public’s safety at heart. Read on for a summary of this story and what it does and doesn’t mean for the future of COVID-19 vaccines.
A brief overview of clinical trials: There are currently several COVID-19 candidate vaccines in clinical trials. Clinical trials are studies measuring the safety and effectiveness of potential new medications or vaccines in humans. I say “potential” medications and vaccines because many never complete the clinical trial process and advance to approval; and that’s a good thing. The U.S. Food and Drug Administration requires all potential new treatments to show convincing evidence that they will help people more than they harm them. If researchers cannot show that a particular vaccine or medicine works, or if it hurts people more than it helps them, then the vaccine or medicine won’t be approved for additional studies nor for use in people.
There are three phases of clinical trials for vaccines, each designed to measure the safety and effectiveness in larger and larger groups of people. The phase 3 clinical trial is the largest phase, involving thousands of people, in order to measure the effectiveness to prevent infection and measure safety in as many people as possible.
The vaccine in question: Researchers from the University of Oxford and AstraZeneca are currently conducting phase 3 clinical trials of a COVID-19 vaccine candidate called ChAdOx1 in the United Kingdom, India, Brazil, South Africa and the United States. ChAdOx1 vaccine uses a weakened form of adenovirus; the genes that the virus needs to make copies of itself have been removed and replaced with genes for the COVID-19 “spike protein” (the spikes that cover the outside of the virus that causes COVID-19). If the ChAdOx1 vaccine works, then vaccinated people will develop immune responses to the spike protein which should protect them against later COVID-19 infection. The researchers previously published the results of a combination phase 1/2 trial in 1077 healthy adults that found higher immune responses after receiving 1 or 2 doses of the ChAdOx1 vaccine compared with people who received a different vaccine, and no serious side effects.
The pause: Last week, the researchers voluntarily paused the phase 3 ChAdOx1 vaccine trial so that an independent team of reviewers and regulators could review a rare and unexpected illness that had occurred in one of the study participants. While the researchers have not publicly revealed the illness, it was reportedly transverse myelitis, a rare inflammation of the spinal cord that can be caused by infection, multiple sclerosis, or autoimmune disorders (in which a person’s immune system mistakenly attacks their own body). Another participant in the same trial had similar symptoms in July, although the first participant was eventually diagnosed multiple sclerosis. The researchers have not revealed whether either illness occurred after the first or second dose of ChAdOx1 vaccine.
What does this mean for COVID-19 vaccine safety? While this is a potential setback for one COVID-19 vaccine, it is also a reassuring sign that the researchers are taking the appropriate steps to ensure that candidate vaccines are safe. As important as it is to have an effective vaccine, it also needs to be a safe vaccine. If there is evidence that a potential vaccine might cause serious side effects, then researchers must study the side effects before giving it to more people, and if the risks outweigh the benefits then a trial should not proceed.
In this instance, regulators in the United Kingdom concluded, after examining the evidence, that the ChAdOx1 vaccine trial is safe to restart in the U.K. While we don’t know yet whether the ChAdOx1 vaccine caused this participant’s transverse myelitis or whether it was caused by something else, it is reassuring to know that U.K. regulators found the trial safe to continue.
Bear in mind that this is only one of several COVID-19 vaccine candidates currently in clinical trials, using many different vaccine technologies. If the data does prove that the ChAdOx1 vaccine caused this illness (and we don’t know that yet), then it wouldn’t necessarily follow that a different COVID-19 vaccine developed using different technologies would cause the same illness. We’ll need to wait and see the data on other COVID-19 vaccines as they are released. In the interim, I hope that vaccine researchers and manufacturers continue to apply the same high standards of safety and effectiveness that the U.S. applies to other vaccines.
Stay safe and healthy,
š Dr. B