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COVID-19 Seems to Spread More Easily Than the Flu: CDC

COVID-19 Seems to Spread More Easily Than the Flu: CDC

Is the coronavirus airborne? What counts as ‘close contact’? Here are the answers you need to protect yourself and your community.

Updated on October 21, 2020 at 11:00am EDT.

It may seem like information about COVID-19 and the coronavirus that causes the disease changes from week to week, or even daily. But there is a reason for that. SARS-CoV-2 is a newly identified coronavirus and scientists are still working to understand how it spreads, how it affects the body and how to manage it.

The good news is that we know a lot more than we did back in February.

Most recently, the Centers for Disease Control and Prevention (CDC) revised its COVID-19 guidance, warning that SARS-CoV-2 spreads more easily than originally thought.

Under certain conditions, it could spread through the air. The CDC also cautions that having close contact with an infected person is risky—even if those encounters are brief, or shorter than 15 minutes.

But what does all this mean exactly? Here’s what we know.

The latest about how COVID-19 spreads
Since the pandemic began, scientists have warned that COVID-19 spreads mainly through contaminated respiratory droplets that are emitted when infected people cough or sneeze and possibly when they breathe or speak.

When these droplets escape the body they may land in a nearby person’s mouth, nose or eyes. They can travel about six feet before settling on a nearby surface. If you touch a contaminated surface then touch your mouth, nose or eyes, you can also become infected.

It is not yet clear how long the coronavirus that causes COVID-19 (SARS-CoV-2) survives on surfaces, but early evidence suggests it may persist for up to several days, depending on the type of surface and other variables, like temperature and humidity.

More recently, however, the CDC revised its guidance on how SARS-CoV-2 spreads. The agency now says that under certain conditions, the coronavirus could also spread through the air.

The agency notes that this is more likely to occur indoors, particularly in areas with poor ventilation or where people are singing or exercising.  

For months, it’s also been generally accepted that brief encounters are less likely to spread SARS-CoV-2 than longer interactions of 15 minutes or more. And while that may still be true, it doesn’t mean that having close contact with others for just a few minutes is risk-free.

The CDC now defines “close contact” as being within 6 feet of those with COVID-19 for a total of 15 minutes or more over a 24-hour period, starting from 2 days before they are tested or develop symptoms until they are isolated.

This means that shorter but repeated exposure that adds up to 15 minutes over the course of one day counts.

Bottom line: COVID-19 spreads very easily. It may spread more efficiently than the flu but, so far, it’s not as contagious as measles, the CDC reports.

Why airborne spread is a big deal
Unlike contaminated respiratory droplets, airborne spread involves aerosols—even smaller particles that may waft and linger in the air.

Certain medical procedures, such as intubations, are known to emit aerosols. But if SARS-CoV-2 is able to spread through aerosols emitted when infected people breathe, shout, sing or speak, the public health consequences are more serious.

This has major implications for businesses, schools, gyms, places of worship and other settings where people congregate indoors.

Why? Compared to aerosols, big respiratory droplets fall more quickly (or within about six feet of an infected person). It’s much harder to avoid smaller particles that drift in the air over greater distances. This is especially true indoors, where these wafting airborne particles are able to accumulate.

This update isn’t entirely new
The World Health Organization (WHO) updated its guidelines on how COVID-19 spreads from one person to another back in July. At the time, the organization warned that the coronavirus could possibly linger in the air indoors, particularly in crowded spaces with poor air flow.

This update was made just three days after a group of 241 scientists pressured WHO officials to recognize airborne spread of the coronavirus.

The letter, published on July 6 in Clinical Infectious Diseases, stated that there is enough evidence to demonstrate "beyond any reasonable doubt" that SARS-CoV-2 can spread not only through larger respiratory droplets from coughs or sneezes, but also through the inhalation of smaller, microscopic droplets in the air—farther away than six feet from an infected person.

The CDC didn’t update its guidelines, warning about the possibility that the coronavirus could spread through the air until October.

Why? Some experts suspect that public health information about COVID-19 became politicized ahead of the November 2020 elections. But the hesitation to call SARS-CoV-2 airborne could have been due, at least in part, to decades-old debate about whether or not respiratory viruses, including the flu, are airborne.

Despite calls for caution, are also still many unknowns. A September 2020 review published in Environmental Research points out that scientists are still working to understand how environment could affect airborne transmission of SARS-CoV-2. The researchers noted that variables like air flow, humidity, temperature and sunlight could render aerosols less infectious.

When it comes to the airborne spread of SARS-CoV-2 and some other respiratory viruses, it’s also unclear how many infectious aerosols are produced by speaking, breathing or singing and how much is required to cause infection.

Proper ventilation can help
There are some things you can do to minimize your risk of exposure to SARS-CoV-2, particularly indoors.

People should “avoid crowded places, close-contact settings, and confined and enclosed spaces with poor ventilation,” the WHO cautions. The group adds that it’s also important to wear cloth face masks indoors, particularly in congested spaces.

Health experts also recommend the following precautions:

  • Increase circulation of outdoor air as much as possible while indoors. That means opening windows, doors and turning on fans and keeping the air moving when you’re inside.
     
  • Don’t linger in crowded settings. The rule of thumb for exposure to SARS-CoV-2 is close contact with an infected person for a total of 15 minutes in a 24-hour period. Crowded indoor settings, such as bars, restaurants, nightclubs and gyms—where people are in one place for a prolonged period of time—are riskier than a quick trip to an uncrowded store to buy essentials or a walk in the park where people can spread out more effectively.

If more research supports the idea of airborne transmission, businesses, schools, nursing homes and other public places may need to improve indoor ventilation with high-efficiency air filtration systems and also install germicidal ultraviolet lights, which can help destroy viruses, bacteria and other pathogens, the authors of the July 6 letter advise.

Keep your hands clean
Many of the common-sense steps you already take to avoid the flu and other common germs may also help in protecting against COVID-19.

Washing your hands often and thoroughly with soap and water for at least 20 seconds is one of the most effective ways to protect yourself against respiratory illnesses, including COVID-19.

If you don’t have access to soap and water, using an alcohol-based hand sanitizer is a good alternative—if you pick the right one and use it frequently and properly.

Choose a hand sanitizer than contains at least 60 percent alcohol, the CDC recommends. Before applying the liquid or gel, remove as much dirt or debris from your hands as possible. Read the product label for instructions and apply as much as directed to ensure its effectiveness. Then, rub the sanitizer over all surfaces of your hands until they are dry.

Be sure that your hands are clean before eating or touching your eyes, mouth or nose, after using the bathroom and while working in the kitchen.

Spread out and wear a mask
Another important step you can take to help curb the spread of COVID-19 is to practice social distancing, or “remaining out of congregate settings, avoiding mass gatherings, and maintaining distance (at least 6 feet) from others when possible,” according to the CDC.

Social distancing is not only intended to reduce the total number of people who become infected with COVID-19 but to also help slow its spread, which could ultimately save lives.

You should also wear a face covering if you go out in public. As confirmed cases of COVID-19 continue to surge, mounting evidence suggests that people with mild or no symptoms at all may be spreading the virus unknowingly. Researchers caution that these so-called “silent spreaders” are making the pandemic much more difficult to control.

Since people may be unwittingly passing the infection on to others—even when they feel fine—asking only sick people to wear masks and stay home in isolation likely isn’t enough to “flatten the curve” and slow the spread of COVID-19.

Essentially, everyone should assume that they may be a carrier of SARS-CoV-2.

Wearing a mask doesn't guarantee you protection against COVID-19—or any other serious upper respiratory infection, like the flu or measles. But many experts argue that whatever protection masks do provide is simply better than nothing. This measure is intended to protect others from you—and not just protect you from the virus.

More ways to avoid infection
Some other general precautionary steps you can take to avoid germs, including COVID-19 and the flu, include the following:

  • Avoid anyone who is or appears to be sick and stay home if you develop symptoms or suspect that you are sick.
     
  • Cover your cough or sneeze with an unused tissue, then throw the tissue in the trash. If you don’t have a tissue, use your upper sleeve or elbow—not your hands.
     
  • Clean and disinfect commonly used objects and surfaces you come into contact with throughout your day, such as computer keyboards, cell phones, doorknobs, faucets and bathroom fixtures with household cleaning sprays or wipes. At work, keep tissues, soap, alcohol-based hand sanitizer and antiseptic wipes on hand. Effective products include diluted household bleach solutions or cleaners with at least 70 percent alcohol as well as most common EPA-registered household disinfectants.
     
  • Avoid sharing personal items, such as pens, dishes, utensils, water bottles and drinking glasses. Even at home, it’s important to avoid using someone else’s fork, spoon or glass. Avoid sharing bedding with other people or pets as well. Used sheets should be washed at the highest water temperature appropriate for the items and dried thoroughly.

It’s also important to do what you can to stay healthy and keep your immune system strong, such as getting quality sleep, following a healthy diet and exercising regularly. Getting a flu shot is also wise. The CDC points out that the symptoms of COVID-19 are similar to those of the flu, and COVID-19 will still be circulating during the 2020/2021 flu season.

In order to protect against the flu and avoid unnecessary evaluation for COVID-19, everyone age 6 months and older should receive a seasonal flu shot.

How you can prepare
Having a plan in place for how you will respond to increasing COVID-19 cases in your area is a good idea. First, be sure to consider anyone in your home or general area who is at greater risk for severe infection and complications, including older people and those with underlying chronic health issues.

Other steps you can take:

  • Make a list of local resources that can help you access information, support, medical attention or other essentials. 
  • Have an emergency contact list, which includes family, friends, neighbors, healthcare providers, employers and other essential phone numbers.
  • Create a "protected space" in your home that can be used to keep household members who are sick isolated from others who are not.

If you might be sick
Anyone who believes they may be infected with COVID-19 or might have been exposed to the coronavirus should take immediate steps to isolate themselves and avoid spreading their illness to others.

If you develop any warning signs of infection you should call your healthcare provider (HCP) for instructions. Before going to a doctor’s office or emergency room, be sure to call ahead and inform the medical staff that you may have been exposed to COVID-19. Your HCP can determine if you need to be tested for the coronavirus.

Medically reviewed in October 2020. 

Sources:
Centers for Disease Control and Prevention. “Coronavirus Disease 2019 (COVID-19): When to Quarantine.” Sept 10, 2020.
Centers for Disease Control and Prevention. “Coronavirus Disease 2019 (COVID-19): How COVID-19 Spreads.”  Oct 5, 2020.
Centers for Disease Control and Prevention. “CDC Media Telebriefing: Update on COVID-19.”
Centers for Disease Control and Prevention. “Coronavirus Disease 2019 (COVID-19) in the U.S.”
Centers for Disease Control and Prevention. “Coronavirus Disease 2019 (COVID-19) Situation Summary.”
Centers for Disease Control and Prevention. “Traveler’s health: Novel Coronavirus in China.”
United Nations. "Coronavirus emergency: here’s what we know so far."
World Health Organization. “Q&A on coronaviruses (COVID-19).”
Centers for Disease Control and Prevention. “Coronavirus Disease 2019 (COVID-19): Prevention & Treatment.”
Centers for Disease Control and Prevention. “What to Do If You Are Sick With Coronavirus Disease 2019 (COVID-19).”
Centers for Disease Control and Prevention. “Update: Public Health Response to the Coronavirus Disease 2019 Outbreak — United States, February 24, 2020.”
Centers for Disease Control and Prevention. "CDC, Washington State Report First COVID-19 Death."
World Health Organization. "WHO Director-General's opening remarks at the media briefing on COVID-19 - 3 March 2020."
Centers for Disease Control and Prevention. "Environmental Cleaning and Disinfection Recommendations"
Centers for Disease Control and Prevention. "Get Your Home Ready."
World Health Organization. “Transmission of SARS-CoV-2: implications for infection prevention precautions.”
Lidia Morawska, Donald K Milton. “It is Time to Address Airborne Transmission of COVID-19.” Clinical Infectious Diseases. July 2020.
Centers for Disease Control and Prevention. “Contact Tracing for COVID-19.”
Centers for Disease Control and Prevention. “COVID-19 Employer Information for Office Buildings.”
Centers for Disease Control and Prevention. “Considerations for Events and Gatherings.”
Centers for Disease Control and Prevention. “Frequently Asked Influenza (Flu) Questions: 2020-2021 Season.”
Centers for Disease Control and Prevention. “Coronavirus Disease 2019 (COVID-19): How to Protect Yourself and Others.” September 21, 2020.
Penn Medicine. “COVID-19 Transmission: Droplet or Airborne? Penn Medicine Epidemiologists Issue Statement.” August 2, 2020.
Jayaweera M, Perera H, Gunawardana B, Manatunge J. “Transmission of COVID-19 virus by droplets and aerosols: A critical review on the unresolved dichotomy.” Environmental Research. 2020;188:109819.
Klompas M, Baker MA, Rhee C. Airborne. “Transmission of SARS-CoV-2: Theoretical Considerations and Available Evidence.” JAMA. 2020;324(5):441–442.

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