OHSU Professor Offers Clues to the Mystery of COVID ‘Super-Dodgers’

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You may know someone – or multiple people – who haven’t gotten COVID-19 yet, even if they were exposed. You might know people who have tested positive and didn’t have symptoms. You might even be one of those people! These people have become known as “super-dodgers.”

There are a few reasons for this phenomenon.

“At the very top of the list, there is a component of luck,” said William Messer, associate professor at Oregon Health & Science University who studies immunology and infectious disease. “That means some people literally dodge the proverbial bullet, which is the COVID-19 virus, over and over and over again.”

That’s because some people might have better immune systems or be more equipped to handle the virus, or some people might have never been exposed.  Even though the likelihood of someone never being exposed is increasingly small as time goes on, there are still some who continue to take many precautions to avoid exposure to COVID-19.

But some people have been exposed multiples times and still never caught the virus. Messer himself, for instance, avoided falling ill even when all three of his household family members got COVID-19. Does this mean Messer is magically immune to COVID-19?

Not at all, he said, because last summer, he caught it at an outdoor event. Looking back, Messer acknowledged that going so long without getting COVID-19 may have made him “overconfident” at the time. He didn’t wear a mask even though the event was crowded.

“This was one of the first, if not the first, public event where I did not wear a mask even when I was in close quarters,” Messer said.

Volume of virus particles

To become infected by any virus, you need to be exposed to an “infectious dose” of particles. A single COVID-19 virus particle isn’t an infectious dose, but a few hundred or thousand might be. If you’re exposed to someone who has COVID-19 but you don’t get sick, it could be because that person wasn’t shedding enough virus particles.

At the beginning of the pandemic, scientists  speculated that relatively few people – dubbed “super spreaders,” referring to those who expose significantly more people to the virus than the average infected person – were responsible for the majority of COVID-19 cases. But time and research revealed that is not the case.

“There are super-spreaders, normal-spreaders and even non-spreaders,” Messer said. “And the proportion of people that fall into each one of those categories isn’t very well worked out. We think that super spreaders are relatively rare. Normal spreaders represent a larger proportion of people spreading the disease. And there are also people who just don’t shed a lot of virus.”

Some people who get COVID-19 have a relatively low number of virus particles in their upper airways or don’t experience symptoms like coughing, so they might not spread the virus as readily as someone with symptoms and a lot of virus particles in their airways.

In Messer’s personal situation, it could be that his family members weren’t shedding enough virus particles for him to get sick. But someone, or more than one person, at the outdoor event was shedding a lot more particles – enough for Messer to become infected, even outdoors.

Genetics

Is there a genetic component to dodging COVID-19 infection or symptoms? Possibly. We know that certain genetic mutations make some people immune to HIV, for example. We also know that if someone has a mild form of sickle cell anemia, they’re immune to malaria. Researchers have been studying whether those who get infected with COVID-19 but do not experience symptoms have a gene that protects them from getting sick.

In research that hasn’t yet been peer reviewed, a team from the University of California, San Francisco, studied 1,400 people who tested positive for COVID-19. Within that group, the team found that people who tested positive but experienced no symptoms were much more likely to have a specific variation in a set of genes that code for certain immune system proteins. In simple terms, people with this genetic variation have a super-charged immune response to COVID-19 that can wipe out the virus before it gets a chance to spread.

However, to develop that immune response to COVID-19, someone with that genetic variation must first be exposed to a different coronavirus. COVID-19 is caused by a coronavirus called SARS-CoV-2, but it’s not the only coronavirus out there. Other coronaviruses can cause the common cold.

It’s possible that some people who have previously had a cold caused by a milder form of coronavirus may have some protection against experiencing symptoms when they have COVID-19. But Messer cautioned that he hasn’t seen “convincing evidence that this would allow a person to completely ‘dodge’ COVID-19.”