Covid 19

How COVID-19 Spreads

COVID-19 is thought to spread mainly through close contact from person to person, including between people who are physically near each other (within about 6 feet). People who are infected but do not show symptoms can also spread the virus to others. Cases of reinfection with COVID-19 have been reported but are rare. We are still learning about how the virus spreads and the severity of illness it causes.

COVID-19 spreads very easily from person to person

How easily a virus spreads from person to person can vary. The virus that causes COVID-19 appears to spread more efficiently than influenza but not as efficiently as measles, which is among the most contagious viruses known to affect people.

COVID-19 most commonly spreads during close contact

  • People who are physically near (within 6 feet) a person with COVID-19 or have direct contact with that person are at greatest risk of infection.
  • When people with COVID-19 cough, sneeze, sing, talk, or breathe they produce respiratory droplets. These droplets can range in size from larger droplets (some of which are visible) to smaller droplets. Small droplets can also form particles when they dry very quickly in the airstream.
  • Infections occur mainly through exposure to respiratory droplets when a person is in close contact with someone who has COVID-19.
  • Respiratory droplets cause infection when they are inhaled or deposited on mucous membranes, such as those that line the inside of the nose and mouth.
  • As the respiratory droplets travel further from the person with COVID-19, the concentration of these droplets decreases. Larger droplets fall out of the air due to gravity. Smaller droplets and particles spread apart in the air.
  • With passing time, the amount of infectious virus in respiratory droplets also decreases.

COVID-19 can sometimes be spread by airborne transmission

  • Some infections can be spread by exposure to virus in small droplets and particles that can linger in the air for minutes to hours. These viruses may be able to infect people who are further than 6 feet away from the person who is infected or after that person has left the space.
  • This kind of spread is referred to as airborne transmission and is an important way that infections like tuberculosis, measles, and chicken pox are spread.
  • There is evidence that under certain conditions, people with COVID-19 seem to have infected others who were more than 6 feet away. These transmissions occurred within enclosed spaces that had inadequate ventilation. Sometimes the infected person was breathing heavily, for example while singing or exercising.
  • Under these circumstances, scientists believe that the amount of infectious smaller droplet and particles produced by the people with COVID-19 became concentrated enough to spread the virus to other people. The people who were infected were in the same space during the same time or shortly after the person with COVID-19 had left.
  • Available data indicate that it is much more common for the virus that causes COVID-19 to spread through close contact with a person who has COVID-19 than through airborne transmission.

COVID-19 spreads less commonly through contact with contaminated surfaces

Respiratory droplets can also land on surfaces and objects. It is possible that a person could get COVID-19 by touching a surface or object that has the virus on it and then touching their own mouth, nose, or eyes.

Spread from touching surfaces is not thought to be a common way that COVID-19 spreads

COVID-19 rarely spreads between people and animals

It appears that the virus that causes COVID-19 can spread from people to animals in some situations. CDC is aware of a small number of pets worldwide, including cats and dogs, reported to be infected with the virus that causes COVID-19, mostly after close contact with people with COVID-19.

Learn what you should do if you have pets.
Currently, the risk of COVID-19 spreading from animals to people is low. Learn about COVID-19 and pets and other animals.

Protect yourself and others

The best way to prevent illness is to avoid being exposed to this virus. You can take steps to slow the spread.

  • Stay at least 6 feet away from others, whenever possible. This is particularly important in preventing the spread of COVID-19.
  • Cover your mouth and nose with a mask when around others. This helps reduce the risk of spread both by close contact and by airborne transmission.
  • Wash your hands often with soap and water. If soap and water are not available, use a hand sanitizer that contains at least 60% alcohol.
  • Avoid crowded indoor spaces and ensure indoor spaces are properly ventilated by bringing in outdoor air as much as possible. In general, being outdoors and in spaces with good ventilation reduces the risk of exposure to infectious respiratory droplets.
  • Stay home and isolate from others when sick.
  • Routinely clean and disinfect frequently touched surfaces and take other steps to stop the spread at home.

Pandemics can be stressful, especially when you are staying away from others. During this time, it is important to maintain social connections and care for your mental health.

New Variants of the Virus that Causes COVID-19

Information about the characteristics of these variants is rapidly emerging. Scientists are working to learn more about how easily they spread, whether they could cause more severe illness, and whether currently authorized vaccines will protect people against them.

What we know

Viruses constantly change through mutation, and new variants of a virus are expected to occur over time. Sometimes new variants emerge and disappear. Other times, new variants emerge and persist. Multiple variants of the virus that causes COVID-19 have been documented in the United States and globally during this pandemic.

The virus that causes COVID-19 is a type of coronavirus, a large family of viruses. Coronaviruses are named for the crown-like spikes on their surfaces. Scientists monitor changes in the virus, including changes to the spikes on the surface of the virus. These studies, including genetic analyses of the virus, are helping scientists understand how changes to the virus might affect how it spreads and what happens to people who are infected with it.

Multiple variants of the virus that causes COVID-19 are circulating globally:

  • The United Kingdom (UK) identified a variant called B.1.1.7 with many mutations in the fall of 2020. This variant spreads more easily and quickly than other variants. In January 2021, experts in the UK reported that this variant may be associated with an increased risk of death compared to other variant viruses, but more studies are needed to confirm this finding. It has since been detected in many countries around the world. This variant was first detected in the US at the end of December 2020.
  • In South Africa, another variant called B.1.351 emerged independently of B.1.1.7. Originally detected in early October 2020, B.1.351 shares some mutations with B.1.1.7. Cases caused by this variant have been reported in the US at the end of January 2021.
  • In Brazil, a variant called P.1 emerged that was first identified in travelers from Brazil, who were tested during routine screening at an airport in Japan, in early January. This variant contains a set of additional mutations that may affect its ability to be recognized by antibodies. This variant was first detected in the US at the end of January 2021.

These variants seem to spread more easily and quickly than other variants, which may lead to more cases of COVID-19. An increase in the number of cases will put more strain on health care resources, lead to more hospitalizations, and potentially more deaths.

So far, studies suggest that antibodies generated through vaccination with currently authorized vaccines recognize these variants. This is being thoroughly investigated and more studies are underway.

Rigorous and increased compliance with public health mitigation strategies, such as vaccination, physical distancing, use of masks, hand hygiene, and isolation and quarantine, is essential to limit the spread of the virus that causes COVID-19 and protect public health.

What we do not know

Scientists are working to learn more about these variants, and more studies are needed to understand:

  • How widely these new variants have spread
  • How the disease caused by these new variants differs from the disease caused by other variants that are currently circulating
  • How these variants may affect existing therapies, vaccines, and tests

What it means

Public health officials are studying these variants quickly to learn more to control their spread. They want to understand whether the variants:

  • Spread more easily from person-to-person
  • Cause milder or more severe disease in people
  • Are detected by currently available viral tests
  • Respond to medicines currently being used to treat people for COVID-19
  • Change the effectiveness of COVID-19 vaccines

CDC, in collaboration with other public health agencies, is monitoring the situation closely. CDC is working to monitor the spread of identified variants, characterize emerging viral variants, and expand its ability to find new SARS-CoV-2 variants. CDC is collaborating with EPA to confirm that disinfectants on EPA’s List N: Disinfectants for Coronavirus inactivate these variant viruses. As new information becomes available, CDC will provide updates.

Testing and International Air Travel

Air travel requires spending time in security lines and airport terminals, which can bring you in close contact with other people and frequently touched surfaces. Social distancing is difficult in busy airports and on crowded flights, and sitting within 6 feet of others, sometimes for hours, may increase your risk of getting COVID-19. How you get to and from the airport, such as with public transportation and ridesharing, can also increase your chances of being exposed to the virus.

Testing before and after travel can reduce the risk of spreading COVID-19. Testing does not eliminate all risk, but when paired with a period of staying at home and everyday precautions like wearing masks and social distancing, it can make travel safer by reducing spread on planes, in airports, and at destinations.

Here is what to know:

  • If you are eligible, get fully vaccinated for COVID-19. Wait 2 weeks after getting your second vaccine dose to travel—it takes time for your body to build protection after any vaccination
  • Get tested with a viral test 1-3 days before you travel. Keep a copy of your test results with you during travel in case you are asked for them.
  • Do not travel if you test positive; immediately isolate yourself, and follow public health recommendations
  • All air passengers coming to the United States, including U.S. citizens, are required to have a negative COVID-19 test result or documentation of recovery from COVID-19 before boarding a flight to the United States. See the Frequently Asked Questions for more information about this requirement.
  • Get tested 3-5 days after travel AND stay home and self-quarantine for 7 days after travel.
  • Even if you test negative, stay home and self-quarantine for the full 7 days.
  • If you do not get tested, it is safest to stay home for 10 days after travel.
  • Always follow state and local recommendations or requirements related to travel.
  • Delay your travel if you are waiting for test results.

Get Tested Before Your Flight

Below is what you need to know about getting tested before your international flight.

  • Get tested with a viral test 1-3 days before your trip and again no more than 3 days before your return flight to the United States departs.
  • Make sure you get your test results before you travel. If you are waiting for results, delay your travel.
  • Do not travel if your test result is positive; immediately isolate yourself and follow public health recommendations.
  • A negative test does not mean that you were not exposed or that you will not develop COVID-19. Make sure to wear a mask, avoid crowds, stay at least 6 feet/2 meters (about 2 arm lengths) from others, wash your hands, and watch your health for signs of illness while traveling.
  • Keep a copy of your test results with you during travel. You may be asked for them.

Get Tested and Stay Home After Travel

  • Get tested with a viral test 3-5 days after travel AND stay home and self-quarantine for a full 7 days after travel.
  • If you do not get tested, stay home and self-quarantine for 10 days after travel.
  • Avoid being around people who are at increased risk for severe illness for 14 days, whether you get tested or not.

Follow all state and local recommendations or requirements after travel.

Also, take these actions after you return from travel to protect others from getting COVID-19:

  • Avoid crowds and stay at least 6 feet/2 meters (about 2 arm lengths) from anyone who did not travel with you. It’s important to do this everywhere — both indoors and outdoors.
  • Wear a mask over your nose and mouth when in public settings. Masks are required on planes, buses, trains, and other forms of public transportation traveling into, within, or out of the United States and in U.S. transportation hubs such as airports and stations.
  • If there are people in the household who did not travel with you, wear a mask and ask everyone in the household to wear masks in shared spaces inside your home for 14 days after travel.
  • Wash your hands often or use hand sanitizer with at least 60% alcohol.
  • Avoid being around people who are at increased risk for severe illness.
  • Watch your health: Look for symptoms of COVID-19.

Frequently Asked Questions

Where do I get tested?

Visit your state, territorial, tribal and local health department’s website to look for the latest information on where to get tested.

What kind of test should I get?

You should get a viral test that can determine if you are currently infected with COVID-19. Learn more about testing for a current infection.

What else should I do before I travel to protect myself and others from COVID-19?

For 14 days before you travel, take everyday precautions like wearing masks, social distancing, and handwashing, and avoid the following activities that put you at higher risk for COVID-19:

  • Going to a large social gathering like a wedding, funeral, or party.
  • Attending a mass gathering like a sporting event, concert, or parade.
  • Being in crowds like in restaurants, bars, fitness centers, or movie theaters.
  • Taking public transportation like planes, trains or buses or being in transportation hubs like airports.
  • Traveling on a cruise ship or river boat.

Is one test enough to prevent spread during my travel?

CDC recommends getting tested 1-3 days before your flight AND 3-5 days after your trip AND stay home and self-quarantine for 7 days. Even if you test negative, stay home and self-quarantine for the full 7 days. If you do not get tested, stay home and self-quarantine for 10 days. Getting tested in combination with staying home significantly reduces travelers’ risk of spreading COVID-19.

What if I recently recovered from COVID-19?

CDC does not recommend getting tested again in the three months after a positive viral test if you do not have symptoms of COVID-19. If you have had a positive viral test in the past 3 months, and you have met the criteria to end isolation, travel with a copy of your positive test result and a letter from your doctor or health department that states you have been cleared for travel. You will need to show this documentation of recovery from COVID-19 before you board a flight to the United States.