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CBC broadcast: The virus is very difficult to contain. Many experts studying the pandemic have said one reason for that is because of silent spreaders. That’s why it came as a bit of shock to hear this yesterday from the World Health Organization.
Maria Van Kerkhove, infectious disease epidemiologist and technical lead for Covid-19, World Health Organization: It still appears to be rare that an asymptomatic individual actually transmits onward.
NBC broadcast: A bombshell assertion suggesting transmission from patients who do not show symptoms is actually not very common.
Dr. Sanjay Gupta: Recently there’s been some confusion about how the coronavirus actually spreads.
Last week an official at the World Health Organization said asymptomatic transmission of the virus appears to be rare.
Now this seemed to contradict what many experts — myself included — have been saying for months. That is, even if you don’t feel sick, you could still be spreading the virus.
Now, a day later, the World Health Organization did clarify their position.
But a lot of people are still left wondering. … What is the truth here? Can you spread coronavirus to others, even if you don’t have symptoms?
So today I’m going to clear up what we know — what the evidence is — about asymptomatic transmission.
Right off the bat, I want to be clear.
Evidence suggests that yes, people can spread the coronavirus even if they don’t appear to have any symptoms.
Dr. Anthony Fauci, director, National Institute of Allergy and Infectious Diseases: The evidence that we have, given the percentage of people, which is about 25, 45% of the totality of infected people, likely are without symptoms. And we know from epidemiological studies that they can transmit to someone who is uninfected even when they’re without symptoms.
Gupta: So what is all this confusion about then?
Some of it may boil down to how you define “asymptomatic.” In fact, there are three terms that sometimes get grouped together under the asymptomatic umbrella. So let’s go through them one by one quickly.
First, asymptomatic infection.
Patients with true asymptomatic infection have the virus, but don’t have symptoms and never get symptoms.
Because of this, they may not seek out or qualify for testing for Covid-19. That makes it difficult then to know precisely how much asymptomatic transmission is actually happening.
Here’s Dr. Mike Ryan, executive director of the WHO Health Emergencies Programme:
Dr. Mike Ryan, executive director, WHO Health Emergencies Programme: Whatever proportion of the disease is transmitting from asymptomatic individuals, that is unknown. And that is occurring. I’m absolutely convinced that that is occurring. The question is how much?
Gupta: So, we do believe asymptomatic spread is happening. We just don’t know the extent.
But now let’s look at the second term — pre-symptomatic infection.
That means you do have the infection, you don’t feel sick now, but you do get symptoms later.
Now there has been a lot of study on pre-symptomatic transmission, and it does seem to play a big role in how coronavirus spreads.
A study published in the science journal Nature looked at 94 coronavirus patients. And they estimated 44% of those patients were exposed to the virus by someone who was pre-symptomatic.
You may be wondering — how can so many people have coronavirus with no symptoms yet?
Well remember, this virus does have a lengthy incubation period — that’s the time period between when someone gets exposed to the virus to when they start showing symptoms. According to Harvard Medical School, the incubation period for Covid-19 is anywhere from three to 14 days, with symptoms typically appearing “within four or five days after exposure.”
Now here is an important point.
Studies have also shown that people may be most contagious just before they start to show symptoms.
Let me repeat that: People may be most contagious right before they start to show symptoms.
During this period, people tend to have more virus in their nose and their mouth. And they can be more likely shedding that virus into the environment … inadvertently infecting others.
Now on top of all of this, there’s a third category you need to consider — you may not have heard of this one. It’s called paucisymptomatic infection.
Pauci — p-a-u-c-i … It means little or few.
That’s when you have symptoms, but they’re either very mild or atypical for Covid-19.
Some people who think they’re asymptomatic actually end up being paucisymptomatic. For example, someone might have a runny nose or some other very mild symptom that they really didn’t think much of. But actually, it turns out to be Covid-19.
Van Kerkhove: We know a number of them who are reported as asymptomatic actually may have mild disease. They may go on to develop symptoms, but we don’t know. I mean, we don’t have a clear picture of this. We’re six months into a pandemic. There’s a huge amount of research that is being done. But we don’t have that full picture yet.
Gupta: So again, there’s a lot that we are still learning. But we can say with confidence that people in all three of these categories — asymptomatic, presymptomatic and paucisymptomatic — are all capable of transmitting the virus to others.
Here’s Dr. Fauci again.
Fauci: The range of manifestations are extraordinary. You can have people who are infected and have no symptoms. You can have people who are infected and have mild symptoms that they barely notice. Others have more severe symptoms. So the range is extraordinary.
Gupta: These different terms and categories are important for researchers trying to understand how this virus works.
But for most of us, these distinctions may be beside the point. Because you can’t neccesarily know what category you fall into. Even if you have no symptoms today, there’s no way for you to accurately predict if you’re going to feel sick tomorrow or the next day.
That’s why the safest thing to do is to act as if you could spread the virus to someone else. That means following the guidelines health officials have long been promoting: Practice physical distancing and wear a mask.
We have plenty of evidence now to show both those things can go a long way toward stopping the spread.
We’ll be back tomorrow. Thanks for listening.