Why Tens Of Thousands Of People Are Key To Testing A COVID-19 Vaccine
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Researchers in Miami hold syringes containing either a placebo or the candidate COVID-19 vaccine from Moderna. Their work is part of a phase three clinical trial sponsored by the National Institutes of Health.
Taimy Alvarez/AP
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Taimy Alvarez/AP
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How do researchers know if anybody is actually being exposed to the virus?
In reality, researchers don’t know if the volunteers are getting exposed to the virus, but they try to conduct trials in areas where the virus is known to be circulating in the community.
Picking a good location is tricky.
«It’s not that you actually want there to be a lot of virus there right at the moment you get the first injection,» Karron says. That’s because it takes several weeks after that first injection for a person’s immune system to respond in a way that would protect them from disease. So researchers must try to predict where the virus will still be circulating weeks or months into the future.
How did researchers decide on their target of 30,000 volunteers?
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Having 30,000 volunteers participate is also partly because there’s a need for speed. The key to determining if the vaccine works is to get enough cases of COVID-19 to be able to make statistically reliable comparisons between the vaccinated group and the placebo group. Researchers estimate 150 cases should be enough to prove that a vaccine is at least 50% effective. The large number of volunteers in each study is an effort to make sure those 150 cases occur as rapidly as possible.
Is there a way to show efficacy with fewer people?
There is a way to show efficacy with fewer people, but the approach is ethically fraught. Some have argued for challenge trials in which volunteers are vaccinated and then deliberately exposed to the virus by inserting the virus directly into their noses. But without an effective COVID-19 treatment, researchers in that sort of study could be killing people if the vaccine didn’t work. It’s also likely that volunteers in a challenge trial would be healthy, young individuals. Their response to the vaccine might be different from the way older people or people with medical conditions might respond. What’s more, a small-scale challenge trial would not reveal any rare side effects a vaccine might cause.
When will the vaccine studies underway have results?
It’s impossible to say for certain when some of the studies will have results, but some scientists and public health officials estimate it could be as early as the end of October.
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