Some people seem unable to catch COVID, scientists are trying to figure out why

One of the lingering mysteries of the COVID-19 pandemic is why some people get infected without getting sick and others don’t get infected at all despite exposure.

Beyond a few known risk factors, it’s mostly dumb luck that determines how someone will fare if exposed to the virus that causes COVID, according to some researchers.

But they’re still trying for more scientific answers by studying people who agree to be intentionally exposed to the virus, yet escape its effects.

People like Faith Paine, 26, of London, who volunteered for a so-called challenge trial — meaning researchers dribbled the coronavirus up her nose, intending to get her sick.

For 17 days last year, Paine had to stay in a single room at London’s Royal Free Hospital, unable to leave, exercise or see anyone who wasn’t encased in a hazmat suit. The food was the worst part, she said, ordered ahead for her entire stay and more appropriate for an airplane ride than a regular diet.

Amid all of the poking and prodding, she was allowed to go to bed only after 11:30 p.m. and was awakened by 6:30 a.m. She felt awful the whole time but wasn’t sure whether it was for lack of sleep and bad food or because she had COVID.

Turns out she didn’t have it.

Like half of the 36 Britons who were paid about $6,500 to be willingly exposed to COVID, Paine never developed an infection and never shed any virus.

Dr. Andrew Catchpole, who helped lead the research, said he didn’t expect everyone to get sick. Catchpole runs regular challenge trials for infections like the flu and always aims for about 50% to 70% to fall ill to ensure that he’s giving the participants enough virus to infect them but not an unsafe amount.

But it didn’t take much virus to give those 18 people COVID, and though the data are still being analyzed, the researchers have yet to identify a clear reason why the others didn’t catch it or why some of those who did never reported significant symptoms.

“The great unknown — the X factor that has yet to be discovered,” said Catchpole, chief scientific officer of Open Orphan, the company that ran the study.

Infection — or the lack of one — mainly has to do with chance combination of multiple factors, he and other experts said.

Those elements include the amount of exposure, genetics, and immunity — “all factors which we are not aware of going on in our bodies and the environment, which affect all these things,” Catchpole said.

For Paine, all of the poking and prodding she went through — and the fact that she was chosen for the trial from 26,000 people who volunteered — was a happy reminder she’s among the healthiest of humans.

“It’s quite nice to know everything is ticking along quite nicely,” she said.

It never crossed her mind to quit the study early.

“If this is the two and a half weeks I have to give up to provide research to shorten the time we all have to live with this, that’s absolutely nothing,” she said.

For someone who’s vaccinated, the degree of exposure is likely to be key to whether they get sick, said Florian Krammer, a virologist at the Icahn School of Medicine at Mount Sinai in New York.

That’s why “social distancing” from sick people and mask-wearing reduces the likelihood of getting sick.

“It’s really just a question of not getting exposed in the right amount,” Krammer said.

With infectious diseases like HIV, malaria and the stomach bug, it’s only rare individuals who have a genetic gift that allows them to avoid falling ill.

And just as studying those outliers can offer insights into those diseases and potentially lead to treatments, Dr. Andrs Spaan, a microbiologist at The Rockefeller University in New York City, hopes to learn more about COVID by studying people who don’t get it.

No one knows how many people have such natural resistance to COVID.

When Spaan and his colleagues published their initial findings last fall, they were inundated with 7,000 emails from people all over the world offering to participate in their research. So far, he said, the group, which now includes 150 partners, has enrolled 700 volunteers.

Often, there’s a price to pay for genetic resistance to disease, he said. Genes that confer resistance to malaria, for example, also increase risk for sickle cell disease, a lethal and extremely painful blood disorder.

Still, Spaan said, it’s crucial to study these individuals.

“By studying how human genetics works against COVID, there may be evidence for therapeutics,” he said.

Read more at USA Today.