Does the amount of coronavirus you're exposed to determine how sick you get? Growing evidence suggests that viral dosage does play a role in illness severity.
Social Distancing Does Make a Difference
Over the last nine months, your life has probably changed dramatically. Don't believe us? Answer this question: How many people outside your household have you engaged with in a long face-to-face conversation with since the pandemic started?
The answer is probably few to zero if you've been taking every coronavirus protection measure you can. Perhaps you've had socially distant meetups with friends where you ate a meal outside or talked to each other from afar. But when was the last time you found yourself in a crowded indoor environment surrounded by strangers not wearing face masks? If you're like us, that was probably around early February, right before the whole world shut down.
But don't fret; all of our social sacrifices haven't been for nothing. Our deliberate change in behavior has decreased our chances of coming into contact with COVID-19. And it also reduced the probability of exposure to large amounts of the virus. It turns out that wearing masks everywhere and practicing social distancing is helping humanity combat this crisis.
COVID-19 Load Can Help Us Understand Sickness Severity
Scientists firmly believe that all the measures we've taken — wearing face masks, social distancing, washing our hands frequently — have beein integral in reducing the infectious dose levels that people are exposed to. Now, they're wondering if these efforts are also why hospitalization and death tracking have deviated from confirmed active cases since last spring.
This would crucial implications for epidemiological modeling and how we assess our risks and behaviors if true. Such an insight could inform important questions like when we should wear masks, when we should go out, and when we could potentially return to our offices.
"The amount of virus exposure at the start of infection — the infectious dose — may increase the severity of the illness and is also linked to a higher viral load [in infected patients]," explained Oxford COVID-19 Evidence Service Team members in March. Hard evidence, both old and new, supports this.
Studies from China have shown that the coronavirus amount that patients have in their systems, also known as the viral load, is linked to illness severity of the patient. The Lancet also recently published a large American study that suggested a patient's viral load at diagnosis was an "independent predictor of mortality." Essentially, this means the higher the viral load, the greater the possibility of dying.
How Does Initial Infectious Dose Affect Illness Severity?
So, does the initial amount of coronavirus you're exposed to make a difference in your chances of catching it or surviving it? Evidence may be less clear on this one, but it is mounting.
In May, scientists in the UK gave ferrets varying doses of SARS-COV-2. There was a clear difference in the animals' outcomes. Those given medium and high doses contracted the illness and suffered similar ailments to what humans experience. In contrast, only one ferret from the "low dose" group was infected. It also avoided the worst effects of the disease and recovered with no lingering fatigue or lung scarring.
If this doesn't surprise you, then your views align with several other studies. "There are loads of examples in the literature for symptom severity being dose-dependent for plenty of [other] bugs," explains Francois Balloux, an epidemiologist and geneticist.
Perhaps the most obvious example is the flu. In 2010, an influenza A study concluded there was definitely a clear-cut relationship between viral dose and patient outcomes. The authors stated, "Low dose exposure may lead to infection, due to the high infectivity of the virus, but of those infected only a small proportion may become ill." On the other hand, "Exposure to high doses of virus results in most of the infected subjects also becoming ill."
A 1918 Spanish Flu retrospective study also concluded that the higher fatalities that occurred during the second and third waves could be due to people being exposed to larger infectious dosages instead of a virus mutation, as was previously believed.
Key Takeaways From All of This Research
Since the pandemic is still active, it's best to keep interactions short and brief instead of intense and prolonged. If someone in your home is COVID-19 positive, isolate the infected household member as much as possible.
And don't let up on the mask-wearing and handwashing, especially if you often find yourself in environments that are too crowded for your liking. As the Spanish Flu study predicted, "When exposure to airborne virus is reduced, for instance by population-wide use of face masks, the relative decrease in numbers of illnesses is expected to be greater than the relative decrease in [viral] transmission."
Stay tuned. We'll be following developments in this story closely.
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