- Originally, U.S. officials believed that the novel coronavirus was spread primarily by people with known symptoms.
- Growing evidence indicates that people who are pre-symptomatic can infect others with the new coronavirus.
- Experts recommend social distancing, even if you are not in an at-risk group (opens in new tab) and feel healthy, to slow the spread of COVID-19.
As more businesses and communities put measures in place to prevent the spread of COVID-19, scientists are working as quickly as possible to learn all they can about the disease and the novel coronavirus that causes it. New research is being published almost daily, including recent studies that suggest the virus might spread differently than officials originally thought.
Previously, scientists believed that individuals who were infected with the novel coronavirus were most contagious when their symptoms (opens in new tab) were noticeable. And that does kind of make sense; viruses are passed from person to person through particles, says Dr. Richard Kuhn, Ph.D., a professor of biological sciences at Purdue University. Those particles are released when someone coughs, sneezes or wipes their nose or mouth and then touches a surface.
So, if someone looks sick—sneezing, coughing or running a fever—you would assume that they are more likely to get others sick. Current CDC guidelines specifically state that, “People are thought to be most contagious when they are most symptomatic,” and that, “Some spread might be possible before people show symptoms; there have been reports of this occurring with this new coronavirus, but this is not thought to be the main way the virus spreads.” (It also states, however, that "COVID-19 is a new disease and we are still learning how it spreads, the severity of illness it causes, and to what extent it may spread in the United States.")
New research is showing that individuals may not have to be displaying symptoms of COVID-19 to be contagious.
A study published on MedRxiv about the outbreaks in Tianjin, China, and Singapore in January and February found that a significant number of infections can be attributed to people who had not yet developed symptoms. (It is worth noting that the study has not yet been peer-reviewed.) Of the COVID-19 cases in Singapore that were studied, it is thought that 48 percent of the cases were transmitted by someone who was pre-symptomatic. In Tianjin, China, that number was 62 percent.
In a recent letter in the New England Journal of Medicine (opens in new tab), researchers noted another circumstance in which two individuals who had recently returned to Germany from Wuhan, China, appeared to be asymptomatic, but tested positive for COVID-19 (opens in new tab) when they were given a throat swab. "We discovered that shedding of potentially infectious virus may occur in persons who have no fever and no signs or only minor signs of infection," researchers wrote in the letter.
Bill Gates wrote his own letter in the New England Journal of Medicine (opens in new tab) in February that expressed similar concerns.
"COVID-19 is transmitted quite efficiently," he wrote. "There is also strong evidence that it can be transmitted by people who are just mildly ill or even pre-symptomatic. That means COVID-19 will be much harder to contain than the Middle East respiratory syndrome or severe acute respiratory syndrome (SARS), which were spread much less efficiently and only by symptomatic people."
While this new research contradicts initial thoughts about the virus, Kuhn doesn’t find this information too surprising. “There are a lot of viral infections that start and begin to produce new viruses before someone begins to feel ill,” he says. “It’s unfortunate because it doesn’t give us a head start, it doesn’t give us a hint that someone’s infected, and it creates real problems.”
Novel coronavirus is not the first disease where someone can appear perfectly healthy but still be contagious. For example, Kuhn says, you can have the flu but not be coughing or feverish yet and still pass on the illness to someone else.
“Even if you’re feeling completely healthy, if you do have a virus and it is actively replicating, it only takes one cough or one sneeze or you wiping your nose and then touching a countertop for those viral particles to be transferred," he says. "It seems like this is a pretty infectious virus, so not many virus particles are probably required to initiate infection.” What this means is that this particular type of coronavirus seems to be especially contagious and can be passed through just a small number of virus particles. Kuhn says that even so much as touching a door handle that someone with the virus has touched could potentially transmit it from one person to another.
This is why taking preventative measures like social distancing are so important.
While our understanding of the new coronavirus may be changing, what experts have been recommending as the best ways to protect yourself from infection (opens in new tab) remain the same. In fact, this new research may even emphasize how important taking preventative measures like washing your hands (opens in new tab) and social distancing (opens in new tab) actually are.
Per the CDC, social distancing means avoiding large gatherings and staying approximately 6 feet away from other people whenever possible. On Sunday, March 15, the CDC released new recommendations to cancel events of more than 50 people throughout the United States for the next eight weeks.
Social distancing helps to slow how quickly a virus spreads and limit the potential of infecting high-risk populations. While you might be a healthy adult without any symptoms, you still run the risk of transmitting the new coronavirus to someone whose immune system might not be as well-equipped to handle the virus.
Kuhn also notes that, while doing things like working from home or staying in on the weekends instead of going out might be disruptive, they are also essential for helping to limit the spread of the virus. Especially while scientists continue to research more about this virus, you should continue to take the necessary precautions and follow the CDC's recommendations, he says.
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