People can help prevent the transmission of SARS-CoV-2, the virus that causes COVID-19, by taking a test after a known exposure. The Centers for Disease Control and Prevention (CDC) recommend testing at least 5 days after exposure.
However, tests are imperfect, so they may not detect all cases of the disease. If a person thinks they have had exposure to COVID-19, it is a good idea to take multiple rapid tests.
People can also greatly reduce their risk of transmitting the virus by assuming they are positive until they have a negative test. They can also self-isolate — even with a negative test — if they develop any symptoms.
Read more to learn when to test for COVID-19, the different types of tests available, and how to access tests.
All data and statistics are based on publicly available data at the time of publication. Some information may be out of date. Visit our coronavirus hub for the most recent information on the COVID-19 pandemic.
When a person decides to test for COVID-19 depends on when they were exposed, if they have symptoms, and more. It is important to consider these factors — especially if a person has limited access to tests.
The incubation period is the time between a person’s exposure to an infection and the onset of their symptoms. Usually, a person with an infection will test positive once they start showing symptoms. Even if they test negative during the incubation period before showing symptoms, they can still test positive after the incubation period.
However, various strains of the virus may have different incubation periods. For instance, the BA.1 Omicron variant has a shorter incubation period than previous versions of the virus.
A 2022 study of 77 symptomatic people with the Omicron variant found that, on average, people experienced symptoms after about 2.8 days. This was 4.5 days for the Alpha variant, the original strain of the virus.
The latency period lasts from exposure to the time of testing positive. During the latency period, a person can be contagious to others but not display any symptoms.
Typically, the incubation and latency periods overlap, but the latency period is slightly shorter.
The original SARS-CoV-2 virus and early variants had latency periods of
For newer variants, both the latency and incubation periods have shrunk drastically. There is currently no research on the length of these periods for newer variants.
When to take a test
A person may want to begin testing as early as 1–2 days after a known exposure and continue testing for up to a week.
However, there is evidence that it may be beneficial to test soon after a known exposure and that testing too late can produce a false negative.
A 2021 study suggests that viral load peaks between days 4–6, then rapidly drops. However, this study only looked at early SARS-CoV-2 transmission prior to widespread infections with new variants, so these numbers likely vary.
Despite this, the sudden drop in viral load means testing too late might produce a false negative.
The same study found that on a population level, more frequent testing would produce more positives and potentially help slow the spread of the virus. This suggests that taking multiple tests is the best way to determine if a person has SARS-CoV-2.
COVID-19 tests fall into two categories: rapid and laboratory.
Home COVID-19 tests are tests a person can do at home. Most offer instant or near-instant results and are generally more affordable and accessible.
While there may be more room for testing errors, an article in The New England Journal of Medicine notes that taking many rapid tests is more effective at detecting infection than having a single expensive lab test at one point in time.
Tests in a medical office can be either rapid or laboratory tests. Laboratory tests usually take a few days for results.
Although some research indicates these may be more accurate, a 2022 study found similar testing accuracy among home tests with Delta and Omicron variants. The results were most accurate if a person tested multiple times.
Every household in the United States can access a free batch of tests from the U.S. government by signing up here. People can also purchase tests online.
For people in the U.S., it is important to only use a Food and Drug Administration (FDA) approved test. The FDA maintains a comprehensive list of approved home self-tests
People who prefer laboratory testing can often get COVID-19 tests at a doctor’s office or other medical centers. Individuals should call before arriving to ask whether the facility has tests and procedures to follow. People can also contact their health insurance provider to check if their plan covers COVID-19 tests.
The Department of Health and Human Services maintains a comprehensive list of testing sites here. Many offer walk-up testing with no appointment necessary.
SARS-CoV-2 primarily transmits through respiratory droplets from a cough or sneeze. A person can acquire the virus when droplets enter their mouth or nose.
This can happen when:
- A person has close contact with someone who coughs, sneezes, or spits when talking.
- A person has droplets on their hand and then touches their nose or mouth.
- A person has close physical contact with someone who has a SARS-CoV-2 infection.
Acquiring the infection is more likely when a person has close contact with another person in a poorly ventilated space for a prolonged period of time.
The following section answers some common questions about when to test for COVID-19.
What should I do if I think I have COVID-19?
A person who thinks they have COVID-19 should behave as if they do. This means isolating from others and wearing a well-fitted, high quality mask if they must be around other people.
It is important to test to verify the infection and to help with determining how long to quarantine. The
What if I am vaccinated and boosted?
Should I retest if my test is negative?
While the CDC does not officially recommend retesting, data shows that frequent testing — especially at-home tests — may increase the likelihood of getting an accurate positive result.
People who want to significantly lower the risk of spreading the virus may want to test daily for several days.
What if I have no symptoms?
Asymptomatic people may still pass on SARS-CoV-2. Individuals become contagious about
A person who thinks they have no symptoms could just not have developed any yet. The CDC
COVID-19 is a highly contagious disease, especially in newer variants. Slowing the spread can help a person avoid missing work or school while protecting vulnerable people and those who cannot get a vaccine.
People who have a recent exposure should, at minimum, test after a few days. A more cautious approach involves testing daily and continuing to wear a mask.