COVID-19 is spread through aerosol droplets when we breathe, speak or sing. The virus can be transmitted even if someone is asymptomatic. If you believe you have COVID-19 or had an exposure, you should immediately isolate yourself from others and seek a PCR or rapid antigen test. If you had COVID-19, you could be around others if 10 days have passed since your first symptoms, symptoms are improving, AND you have had no fever for at least 24 hours without taking fever-reducing medications.
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How COVID-19 Spreads
The SARS-CoV-2 virus initially infects, replicates, and spreads from the nose and the mouth. Whenever one breathes, speaks, coughs, or sneezes, we produce turbulent airflow in the upper respiratory mucosa. Through the production of a shearing force, this airflow creates microscopic respiratory droplets and aerosols that are emitted from the nose and mouth into the surrounding air. When you are infected, viral particles are captured within these droplets and aerosols.
Depending upon their size, droplets will often follow a ballistic trajectory subject to gravity and fall to the ground within a few seconds. Often 10 microns or less, aerosols are commonly caught in air currents and may float or drift for hours. When an infected person emits these particles, they may land in the nose or mouth of infected persons. An uninfected person may also inhale them into the deeper respiratory tree. Spread can also occur through contact with objects that harbor the virus.
How Contagious is COVID-19
Researchers say that, on average, every person who has COVID-19 will pass it on to 2 or 2.5 others. One study says that number is even higher, with one sick person infecting between 4.7 and 6.6 others.
By comparison, someone who has the flu will probably give it to an average of 1.1 to 2.3 others. But one person with measles might spread it to 12 to 18 others. Although children tend to get infected with the coronavirus less often and have milder symptoms than adults, they can still catch and spread it.
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When COVID-19 is Most Contagious
According to Harvard Medical School, people can spread COVID-19 48 hours before showing symptoms. A recent study in The Lancet suggests that people are most contagious during the first 5 days of illness. All individuals in the study were no longer shedding the live virus after 9 days of illness.
These results indicate that it is essential to wear masks, social distance, and quarantine immediately if you believe you were exposed to someone with COVID-19, as you can spread the virus before you even show symptoms.
When You Can Safely Interact With Others After Having COVID-19
In general, you should self-isolate for 10 days if you were positive for COVID-19 and 14 days if you had close contact with someone who had COVID-19. There is a 14 incubation period for the virus, meaning you can be exposed to the virus and begin to show symptoms up to 14 days later.
Below we outline CDC guidance for people who fall into the following categories:
For Anyone Who Has Been Around a Person with COVID-19
Anyone who has had close contact with someone with COVID-19 should stay home for 14 days after their last exposure to that person.
However, anyone who has had close contact with someone with COVID-19 and meets the following criteria does NOT need to stay home.
- Someone who has been fully vaccinated and shows no symptoms of COVID-19. However, fully vaccinated people should get tested 3-5 days after their exposure, even if they don’t have symptoms, and wear a mask indoors in public for 14 days following exposure or until their test result is negative.
- Someone who has COVID-19 illness within the previous 3 months and
- Has recovered and
- Remains without COVID-19 symptoms (for example, cough, shortness of breath)
I think or know I had COVID-19, and I had symptoms
You can be around others after:
- 10 days since symptoms first appeared and
- 24 hours with no fever without the use of fever-reducing medications and
- Other symptoms of COVID-19 are improving*
*Loss of taste and smell may persist for weeks or months after recovery and need not delay the end of isolation
These recommendations do not apply to people with severe COVID-19 or with weakened immune systems (immunocompromised).
I tested positive for COVID-19 but had no symptoms
If you continue to have no symptoms, you can be with others after 10 days have passed since you had a positive viral test for COVID-19.
If you develop symptoms after testing positive, follow the guidance above for “I think or know I had COVID-19, and I had symptoms.”
I was severely ill with COVID-19 or had a weakened immune system (immunocompromised) caused by a health condition or medication.
People who are severely ill with COVID-19 might need to stay home longer than 10 days and up to 20 days after symptoms first appear. People with weakened immune systems may require testing to determine when they can be around others. Talk to your healthcare provider for more information. Your healthcare provider will let you know if you can resume being around other people based on your testing results.
People who are immunocompromised should be counseled about the potential for reduced immune responses to COVID-19 vaccines and the need to continue to follow current prevention measures (including wearing a mask, staying 6 feet apart from others they don’t live with, and avoiding crowds and poorly ventilated indoor spaces) to protect themselves against COVID-19 until advised otherwise by their healthcare provider. Close contacts of immunocompromised people should also be encouraged to be vaccinated against COVID-19 to help protect these people.
For Healthcare Professionals
If you are a healthcare professional who thinks or knows you had COVID-19, you should follow the same recommendations listed above for when you can resume being around others outside the workplace. When you can return to work depends on different factors and situations.