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Coronavirus disease (COVID-19): How is it transmitted?

Coronavirus disease (COVID-19): How is it transmitted?
23 December 2021 | Q&A

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The English version was updated on 23 December 2021.
We know that the disease is caused by the SARS-CoV-2 virus, which spreads between people in several different ways.
Current evidence suggests that the virus spreads mainly between people who are in close contact with each other, for example at a conversational distance. The virus can spread from an infected person’s mouth or nose in small liquid particles when they cough, sneeze, speak, sing or breathe. Another person can then contract the virus when infectious particles that pass through the air are inhaled at short range (this is often called short-range aerosol or short-range airborne transmission) or if infectious particles come into direct contact with the eyes, nose, or mouth (droplet transmission).
The virus can also spread in poorly ventilated and/or crowded indoor settings, where people tend to spend longer periods of time. This is because aerosols can remain suspended in the air or travel farther than conversational distance (this is often called long-range aerosol or long-range airborne transmission).
Further research is ongoing to better understand the spread of the virus and which settings are most risky and why. Research is also under way to study virus variants that are emerging and why some are more transmissible. For updated information on SARS-CoV-2 variants, please read the weekly epidemiologic updates .
Whether or not they have symptoms, infected people can be contagious and the virus can spread from them to other people.
Laboratory data suggests that infected people appear to be most infectious just before they develop symptoms (namely 2 days before they develop symptoms) and early in their illness. People who develop severe disease can be infectious for longer.
While someone who never develops symptoms can pass the virus to others, it is still not clear how frequently this occurs and more research is needed in this area.
Both terms refer to people who do not have symptoms. The difference is that ‘asymptomatic’ refers to people who are infected but never develop any symptoms, while ‘pre-symptomatic’ refers to infected people who have not yet developed symptoms but go on to develop symptoms later.
Yes, any situation in which people are in close proximity to one another for long periods of time increases the risk of transmission. Indoor locations, especially settings where there is poor ventilation, are riskier than outdoor locations. Activities where more particles are expelled from the mouth, such as singing or breathing heavily during exercise, also increase the risk of transmission.
The “Three C’s” are a useful way to think about this. They describe settings where transmission of the COVID-19 virus spreads more easily:
The risk of COVID-19 spreading is especially high in places where these “3Cs” overlap.
In health facilities where people are receiving treatment for COVID-19, there is an increased risk of infection during medical procedures called aerosol generating procedures. These can produce very small droplets that can stay suspended in the air for longer periods of time and spread beyond conversational distances (typically 1 meter). This is why health workers performing these procedures or in settings where these procedures are performed should take specific airborne protection measures, including using appropriate personal protective equipment such as respirators. This is also why visitors are not permitted in areas where these procedures are being performed.
There are many things you can do to keep yourself and your loved ones safe from COVID-19. Know your risks to lower risks. Follow these basic precautions:
Read our public advice page for more information.

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This article is based on reporting that features expert sources.
Now that the world is three months into the coronavirus pandemic , scientists have amassed a lot more knowledge about the virus and the disease it causes, COVID-19. We now have a very clear picture of how the virus spreads – and how it does not.
This particular coronavirus is just a new version of a very common pathogen. “It belongs to a family of viruses that have been around forever,” says Dr. Jeffrey A. Linder, professor and chief of the division of general internal medicine and geriatrics at Northwestern University's Feinberg School of Medicine. For instance, other coronaviruses account for perhaps one third of all the common colds that children come down with each year.
There are seven known types of human coronavirus , and four of them circulate throughout the world every year, infecting both children and adults but causing little to no harm. Three others, however, have mutated into more dangerous versions. One caused the outbreak of severe acute respiratory syndrome, or SARS, in 2002-2004. Another was behind Middle East respiratory syndrome, or MERS, which first appeared in 2012. The third is this current version of the virus, known scientifically as SARS-CoV-2 because it is similar to the SARS version.
Because we humans have a long history with these viruses , we already knew a lot about their methods of operation. SARS-CoV-2, it turns out, is pretty typical.
Coronavirus spreads primarily through person-to-person contact. It is a respiratory virus , and, according to the Centers for Disease Control and Prevention, it can be found in water droplets that form from respiration – the act of breathing. This is known as droplet spread.
We naturally and unconsciously spread these droplets when we talk, sneeze, cough and breathe. They are so small and light that they can travel a fairly good distance from your mouth. That is why infectious disease experts want us all to stay 6 feet apart . That is beyond the distance most droplets can usually travel, which is about 2 to 3 feet depending on their size and weight.
In a cough or sneeze, though, they can fly from five to 200 times farther, according to research out of the Massachusetts Institute of Technology. And that’s why it’s important to cover your mouth and nose with your elbow when you do so – and to stay as far away as possible from others who are visibly sick.
The virus can enter our bodies when we breathe these droplets into our own nose, mouth or eyes. They can also gain purchase if we touch another part of our body where they land and then touch our mouth, nose, or eyes. Here, again, you can see the logic behind the warning against touching your face when you may have been in the presence of the virus and to wash your hands often and properly to rid them of the virus.
According to the CDC, scientists believe that people are the most contagious when they are most symptomatic . (Hence, the recommendation that sick people stay home.) However, it appears to be possible that people can spread the virus before symptoms even appear. The virus has an incubation period of between two to 14 days, so it is possible to carry and spread the disease before you know you are sick. The CDC reports that this has occurred during this outbreak, but it is not believed to be the main way the virus spreads.
It may also be possible for you to get the virus by touching some object – a doorknob, a book, a water glass – that has the virus on it and then touching your mouth, nose or eyes.
“When the droplets land on inanimate objects, called fomites, the virus can remain ‘viable’ for an ill-defined length of time,” says Dr. John Swartzberg, clinical professor emeritus of infectious diseases and vaccinology at University of California—Berkeley School of Public Health.
That length of time is currently thought to be somewhere between a few hours and a few days, though, “I don’t think we know yet,” Linder adds. “That is why cleaning surfaces is an important part of control.” Again, experts do not think that this is the main way the virus spreads.
Every germ has different ways of getting into our systems, and ways that it cannot spread to humans. For example, some viruses can circulate through what is known as airborne spread. The virus that causes measles, for example, is the most contagious human virus because, being especially small and lightweight, it can stay suspended in the air for perhaps two hours after an infected person coughs or sneezes. One person with measles can infect 12 to 18 others.
However, “it is unlikely that airborne spread plays an important role in transmission (of SARS-CoV-2). It may occur is the most we can say about this,” Swartzberg says. Current rates of infection seem to show that while the virus is pretty contagious through direct contact, it is rarely transmitted by indirect contact. According to the World Health Organization, SARS-CoV-2 has an infection rate of about 2 to 2.5 people – far less than measles, but more than the seasonal flu , which averages about 1.3.
WHO has also reported that there is no evidence that coronavirus can be transmitted by mosquitoes or other insects. And it does not seem to be carried in food or beverages. The U.S. Food and Drug Administration says there is no current evidence that the virus can be transmitted through food or food packaging that has been shipped from manufacturers to retail outlets. There is a small chance the virus could be carried by food that is packaged for delivery or pickup . To avoid that risk, it is recommended that you take the food out of its packaging, throw that packaging away and then wash your hands thoroughly before eating.
Finally, while the virus is found in stool, “It is unlikely this is an important means of transmission,” Swartzberg says.
Given how the coronavirus spreads and doesn’t spread, Linder says, we know there are four primary ways to prevent infection: “Stay away, wash your hands, clean surfaces and don’t touch your face. That’s why we should all be doing those four things.”
The U.S. News Health team delivers accurate information about health, nutrition and fitness, as well as in-depth medical condition guides. All of our stories rely on multiple, independent sources and experts in the field, such as medical doctors and licensed nutritionists. To learn more about how we keep our content accurate and trustworthy, read our editorial guidelines .
Swartzberg is a clinical professor emeritus of infectious diseases and vaccinology at University of California—Berkeley School of Public Health. He is also chair of the editorial board that publishes the UC Berkeley Wellness Letter and the school's Health After 50 Newsletter.
Linder is a general internist and primary care clinician-investigator and the Michael A. Gertz Professor of Medicine and chief of the division of general internal medicine and geriatrics at Northwestern University's Feinberg School of Medicine.
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A guide to COVID-19 and wellness from the health team at U.S. News & World Report.
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Jessica Migala has been a health, fitness, and nutrition writer for almost 15 years. She has contributed to more than 40 print and digital publications, including EatingWell, Real Simple, and Runner's World. Jessica had her first editing role at Prevention magazine and, later, Michigan Avenue magazine in Chicago. She currently lives in the suburbs with her husband, two young sons, and beagle. When not reporting, Jessica likes runs, bike rides, and glasses of wine (in moderation, of course). Find her @jlmigala or on LinkedIn.

With nearly 5.5 million confirmed cases of coronavirus in the US (and close to 22 million cases worldwide), it's clear that neither COVID-19, nor the anxiety surrounding it, is going anywhere soon.

Because the virus (technically SARS-CoV-2, FYI) that causes this illness is new, lots of the fear surrounding COVID-19 stems from how little we know about it. Luckily, experts do know some pretty important things about the virus' transmission, or how the coronavirus does—and doesn't—spread.

According to the Centers for Disease Control and Prevention , COVID-19 is spread mainly from person-to-person, usually via close contact (within six feet). Simply being near an infected person who coughs, sneezes, or talks can expose you to their infected respiratory droplets, the CDC says. It those virus-containing particles land in your eyes, nose, or mouth, or if you inhale them into your lungs, you could become infected. Some people may be capable of spreading it to others even though they don't have any symptoms, the CDC points out.

You might also acquire the infection if viral particles get on your hands by, say, touching contaminated surfaces or shaking hands with someone whose hands are contaminated with the virus, and then touching your eyes, nose, or mouth. "A sneezing or coughing person will cover their mouth, get it all over their hand, and then touch something that you then touch," Robert Murphy, MD, an infectious disease expert at Northwestern University, tells Health . The virus can then gain entry into your body when you touch your own face, he adds.

One other note: While the virus has been detected in stool, it's still not clear whether it can be acquired through fecal-oral transmission, according to a review posted online March 12 by Clinical Gastroenterology and Hepatology .

Unfortunately, the only way to truly know if someone has COVID-19 is to test them—that's because the symptoms of the illness may look extremely similar to that of the common cold or flu: cough, fever, body aches.

It's also important to know that not everyone who is infected with coronavirus shows symptoms—as is the case with asymptomatic carriers . They can harbor the virus and spread it to other people before developing symptoms. It's also possible for their symptoms to be so mild that they're not aware they have the virus. The CDC estimates that 50% of transmission occurs prior to symptom onset.

The recent coronavirus outbreak sparked a review published in February in the Journal of Hospital Infection , which looked at other coronaviruses (including SARS, MERS, and other endemic human coronaviruses), and determined that they can live on surfaces like metal, glass, or plastic for anywhere from two hours to nine days. Subsequent research in the New England Journal of Medicine found that the virus can live on copper for up to four hours, on cardboard for up to 24 hours, and on plastic and stainless steel for two to three days.

However, investigators examining outbreaks of COVID-19 on three cruise ship voyages in February and March reported the first evidence that the virus may hang around much longer than than initially thought. Traces of the virus were found in the cabins of infected Diamond Princess passengers (including symptomatic and asymptomatic individuals) 17 days after their cabins were vacated, according to the March 23 Morbidity and Mortality Weekly Report from the CDC. However, the authors of the report say the data cannot be used to determine whether the virus from transmitted from person to person through contaminated surfaces.

Even if we don't know exactly how long the virus lingers on surfaces, we do know that disinfecting surfaces is considered "best practice" for helping to prevent transmission of the virus. So again, wiping down common surfaces (and avoiding touching common surfaces if possible) will help decrease the spread. The CDC recommends cleaning tables, countertops, light switches, doorknobs, and cabinet handles regularly. However, it’s unlikely that COVID-19 is spread by mail or packages; if it were, there’d be even more cases, says Dr. Murphy.

It's a fair question—especially since lots of other viruses, like norovirus or other gastrointestinal viruses, can spread via contaminated food. But, while a risk can't be ruled out if an infected person prepares the food, or you buy it from a highly trafficked buffet, the coronavirus doesn't appear to be spread by food, per The New York Times .

Thomas File Jr., MD, chair of the infectious disease division at Northeast Ohio Medical University, and president of the Infectious Diseases Society of America, addressed the topic in a recent media briefing. "I don’t think we're so concerned about produce, although anything that’s being touched by hands, where people could be having the virus on their hands, could potentially be at risk." He recommended that people wash their produce.

The term "community spread" entered the nation's coronavirus vocabulary as outbreaks of disease popped up across the US, initially in densely populated metropolitan areas. According to the CDC, community spread means people in a specific area have been infected, even if they don't how or where they acquired the illness. In other words, they didn't have to know someone with COVID-19 or have a recent history of travel to a place where an outbreak has occurred to become infected.

New York City, once a major epicenter of the disease, experienced rampant community spread early in the pandemic. Today, there are 33 "hot spot" states where the number of COVID-19 cases is on the rise and positivity rates (the percentage of coronavirus tests that come back positive) are rising or persistently high, according to the Henry J. Kaiser Family Foundation .

It only solidifies the need for people to follow the CDC's preventive measures: avoid close contact with other people, especially people who are sick; wear a cloth face covering, especially when social distancing isn't possible; try not to touch your eyes,
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