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By now, most if not all of us know someone who has contracted COVID-19, or in the very least, been exposed to it. A family member, a friend of a friend, a colleague. COVID-19 is everywhere. And the experience often plays out differently from person to person.
Some people are exposed to the virus briefly and go on to develop a severe, life-threatening infection. Others unknowingly spend hours with an infectious person and develop a mild illness. And a lucky handful who are directly exposed to someone with the virus never get infected.
Experts suspect there’s a mix of factors impacting how sick people get after being exposed to the coronavirus. There’s our age and genetics along with underlying health conditions — but the viral load and circumstances in which we’re exposed play a pretty big role, too.
Being exposed to a high viral load generally leads to a rougher go of it. There are ways to minimize how much virus you breathe in, so even if you get exposed, you’ll hopefully get less sick.
Here’s why viral load matters:
Evidence shows that viral load, or the amount of virus a person is exposed to, can influence how sick someone will get.
The best data we have on viral load comes from animal studies. They’ve taught us that, in general, the more virus an animal is exposed to, the sicker they’ll get, said Benjamin Neuman, a virologist and the head of the biology department at Texas A&M University-Texarkana.
A Syrian study conducted on hamsters found that animals injected with a higher SARS-CoV-2 viral load had more severe lesions in the lungs and experienced greater weight loss. With both SARS and MERS, two deadly coronaviruses behind past epidemics, being exposed to higher infectious doses led to worse outcomes.
“Virus particles are like lottery tickets,” Neuman said. “The more you are exposed to, the greater the chance of catching the disease.”
There are a couple reasons as to why viral load impacts the seriousness of an illness. First is that more virus is able to infect more cells, so from the get-go, our immune system is up for a tougher fight.
Neuman said a large viral load also probably has more viral diversity. “A larger number of viruses will usually have a wider range of slight genetic variants. Infecting with pools of virus that contain more mutations also leads to more disease,” he explained.
Viral load alone won’t determine how sick people will get. Other factors like age, co-morbidities and genetics play an even bigger role, according to Ilhem Messaoudi, the director of the University of California, Irvine’s Center for Virus Research.
“The host plays a much more important role in the trajectory of clinical disease,” Messaoudi said.
The circumstances in which a person is exposed are also worth looking at. For example, an intensive care doctor operating on an infected person has a much greater risk of being exposed to a high viral load compared to someone passing an infected person in the grocery store, Messaoudi explained.
Spending time inside near someone with a high viral load who is shedding a ton of virus also increases the risk of picking up COVID-19. Some smaller studies have suggested that people with high viral loads may be more likely to transmit the coronavirus to others, but more research is needed to better understand the link.
Researchers haven’t been able to quantify viral load and determine at what point viral load becomes problematic. “There’s no magic threshold,” Messaoudi said, but ultimately it doesn’t take much for a person to get infected.
Whether we realize it or not, we’re spitting droplets at each other all the time. “Any time you spend talking to someone without a mask on, you’re going to exchange some saliva,” Messaoudi said. If a couple of good viral particles get into our lungs and our body doesn’t generate a robust antiviral immune response in time, infection can occur.
Masks are currently our biggest weapon against the coronavirus.
Studies have shown that face masks can potentially limit the amount of the virus being exhaled into the environment and inhaled. That’s great news when it comes to viral load.
One study (also conducted on hamsters) found a surgical mask partition drastically lowered the rodents’ chances of getting sick, and if they did get sick, the disease was milder. “We can’t say for certain yet, but it seems reasonable to suggest based on animal infection studies that reducing the dose of coronavirus could lead to less severe infection,” Neuman said.
The message is simple: Mask up. Even when people around you are wearing masks and even when you’re in an empty space others use frequently. “If you are in a place where another person has recently been, wearing a mask is a very good idea,” Neuman added.
Remember: the coronavirus is known to spread via aerosols that can hang in the air for a few hours, so a good mask could help protect you from inhaling some of those floating particles. “Masking can prevent up to 70% of transmission, that’s basically as good as one dose of the vaccine,” Messaoudi said.
Ventilation is another useful tool that helps disperse viral particles and break up viral loads.
Being outdoors or opening windows cuts one’s chances of contracting COVID-19 by “effectively diluting the virus in more air, and flushing respiratory droplets out of a closed space quickly,” Neuman said.
You’ll still have to be careful. Ideally, the wind or fans will carry and disperse viral particles away from you, but depending on the air flow pattens, you could still be in harm’s way and inhale enough virus to get sick.
Lastly, if any of your contacts have been exposed, isolating from them for about 10 days — even if they don’t seem sick — is a must.
People tend to have the highest viral loads right before or around the onset of symptoms, so while they might appear to be COVID-free, they also have the potential to expose you to a ton of virus.
*Experts are still learning about COVID-19. The information in this story is what was known or available as of publication.
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