Supported by:
Brown School of Public Health   The Rockefeller Foundation

how testing works—
and why it’s important

COVID-19 testing has never been more important. We know more than ever before about testing and how to use it most effectively to protect others and slow the spread of the virus. Here are some critical reminders:

1 now’s the time to get tested—and to be more careful than ever

We must each embrace regular testing to make it through this pandemic and minimize the number of lives lost. Testing needs to become part of our routines—not only for ourselves, but for our families, communities, networks, and country as well.

And testing is just one step toward getting us over the finish line. We encourage every citizen to get fully vaccinated. Along with vaccination and testing, wearing a mask and washing hands are the best tools to prevent the continued spread of COVID-19.

2 get tested 5 days after being exposed

Understanding the right time to get a COVID-19 test requires knowing how the virus works.

Day 0 – Exposure: The first day someone is exposed to the coronavirus, they have very little virus in their system. They do not feel sick and are not very contagious.

Days 1 – 3 Presymptomatic: Over the next several days, the viruses begin to replicate and spread. While a person likely won’t feel sick yet, they are very contagious and can infect others. This is called presymptomatic spread.

Days 3 – 10 Symptomatic (or not): In the first week after exposure, as the virus replicates, an infected person is the most contagious. Their immune system is also in high gear fighting the virus, leading to feeling sick—though 4 out of 10 people with COVID do not have any symptoms at all.

Knowing this pattern, the ideal time to get a test is on Day 5 or 6 after possible exposure to COVID-19. While waiting to Day 7 or 8 is fine, being tested earlier than Day 5 is not recommended as there MAY NOT be enough virus for the test to work, resulting in a false negative.

3 not sure when you were exposed? Get tested immediately and then test again.

If there’s a window of time when you may have been exposed to COVID-19, you have two options:

  • Get tested as soon as possible after the period of potential exposure. If the test is negative, get tested again on Day 5 or 6—just to be safe.
  • If unvaccinated, you can also quarantine for five days after the period of potential exposure and then get tested.
  • If vaccinated, you should take precautions and wear a well-fitted mask around others until you are able to test five days later.

4 if you have any symptoms, get tested right away.

People who have COVID-19 symptoms are likely far enough along in the illness timeline that they will have a positive test if they have a COVID-19 infection and should get tested right away—though it’s recommended they consult with a health care provider before getting a test.

5 tests are not prevention

You might be wondering what’s behind the public health mantra, “Testing is not prevention.” As screening or surveillance testing rolled out in particularly high-risk locales like college campuses, some people took advantage of the frequent testing and used it to justify taking risks (not to mention putting others at risk). This use of testing is inherently flawed because of what we learned in Reminder #1. A test is a point-in-time measure of whether you have the virus in your system—and if you do—if you have enough virus to show up as a positive case. As we know, the amount of the virus and its detectability vary depending on when you were first exposed. If you get tested too early, and do not have enough virus in your system to prompt a positive result, you are still contagious and capable of spreading to others. For this reason, testing should never be thought of as a “free pass” to take risks. Vaccination, masks, physical distancing, and hand washing are the most tried-and-true prevention methods to be used in combination with testing.

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