The COVID Risk Quiz is a tool intended to help you decide whether you should get tested for COVID-19 in order to keep from spreading the disease to other people. If you get this recommendation, your risk of spreading the disease will be lowest if you get tested before coming into close contact with anyone outside your household. (This Quiz is a decision-support tool only. Results are provided for informational purposes and should not be construed as medical advice.)
It used to be that if you got infected, your risk of getting infected again was a lot lower for a while — usually about three months. Then the Omicron variant arrived. Now, some people can get COVID-19 again within a few weeks, but it's not clear how common that is.
For those reasons, the COVID Risk Quiz assumes that if you got infected within the last 45 days, you have a small amount of protection from getting infected right now.
Screening for COVID-19, also referred to as screening testing or asymptomatic screening, means testing your population to identify infected people who are not showing symptoms. Diagnostic testing for COVID-19 is performed when infection is suspected, such as when the person:
Has COVID-19 symptoms or
Has no symptoms, but has had a recent known or suspected exposure to SARS-CoV-2 (the virus that causes COVID-19).
As of September 26, 2022, only tests that have Emergency Use Authorization (EUA) for use in asymptomatic people can be used for screening. To see which PCR tests can be used, go to this page of the FDA's website and search for "screening." To see which antigen tests can be used, go to this page of the FDA's website and search for "screening."
Both kinds of testing can be done using either a PCR test (also known as a molecular or lab test) or an antigen test (also called a rapid test).
PCR tests look for pieces of the virus’s genetic material. They are the most accurate kind of test for COVID-19 currently available.
Antigen tests look for proteins from the virus. They are designed to be taken at least twice: If you have COVID-19 symptoms, you take one test now, and one test 48 hours later. If you don't have symptoms, wait another 48 hours and take a third test. When used that way, they are nearly as accurate as PCR tests. If you're using antigen tests for screening, you'll need to test more frequently than you would if you were using PCR tests.
Antibody tests (also known as serology tests) look for proteins that your body makes to fight the virus. Those proteins are called antibodies. They can come from a past COVID-19 infection or from a COVID-19 vaccine. Antibody tests cannot be used to diagnose an active infection.
In point-of-care (POC) testing, all testing steps, including sampling and analysis, take place close to or near the patient. For the Workplace Testing Planner and the COVID Risk Quiz, this means that testing is completed either on-site at your organization’s location or in a health-care provider's office, at a testing site, or in your home. Point-of-care tests give you results quickly. Most of them are antigen tests, but some point-of-care PCR tests are available, as well.
In lab-based or off-site testing, samples are gathered on-site at your organization or other testing location and are sent to a central lab for processing and analysis. Lab-based tests are generally PCR tests, which are highly accurate. However, they take longer to return results than point-of-care tests do. In some cases, the turnaround time of lab-based tests is not fast enough to prevent an outbreak in an organization.
Sensitivity refers to how well a test designates someone who HAS the disease as positive.
If you have a test with 95% sensitivity and you test 100 people who have COVID-19, 95 will test positive (true positive) and 5 will test negative (false negative). Tests with high sensitivity will find most cases of the virus. They will return few false negatives.
Specificity is how well a test designates someone who DOESN’T have the disease as negative.
If you have a test with 95% specificity and you test 100 people without COVID-19, 95 will test negative (true negative) and 5 will test positive (false positive). People who test positive using tests with high specificity are very likely to truly have the disease, which means that very few people will be quarantined unnecessarily. These tests return few false positives.
In an ideal world, all tests would be both highly sensitive and highly specific. Unfortunately, that’s not possible most of the time. It’s also important to acknowledge that no test is perfect — no test will have 100% sensitivity and specificity.
When you're using a test to find out if someone has a disease, there are four possible results you can get:
True positive: The test result is positive and the person has the disease.
True negative: The test result is negative and the person doesn't have the disease.
False positive: The test result is positive but the person doesn't have the disease.
False negative: The test result is negative but the person does have the disease.
In an ideal world, all tests would return only true positives and true negatives. Unfortunately, no test is perfect.
PCR tests, also known as molecular tests, look for pieces of the virus’s genetic material using a lab technique called polymerase chain reaction (PCR). They are the most accurate kind of test for COVID-19 currently available.
PCR samples are usually sent for processing and analysis in a lab, and results can take anywhere from a few hours to several days to arrive. Lab-based PCR tests tend to cost more than other test types. Some point-of-care PCR tests are now available, but they typically require purchase of a dedicated instrument and training to run the tests. If you want to use a point-of-care PCR test to screen members of an organization, you may need to purchase multiple instruments and train several staff members for this purpose. Point-of-care PCR tests typically return results in under an hour.
Antigen tests look for viral proteins. These tests typically provide results within minutes and are very good at accurately identifying people who are carrying a lot of virus. They are not as good as PCR tests at finding people who aren't carrying as much virus, including children and asymptomatic adults. If your organization is using this type of test, check how well the brand you use works in the population you’ll be testing (adults vs. children, people with symptoms vs. people without symptoms). Many antigen tests still require trained staff run them, but others are now available over the counter for home use. Antigen tests tend to be the least expensive type of test.
Because of their decreased sensitivity, antigen tests have the following limitations:
If you are using antigen tests to screen members of an organization, you may need to test more frequently than you would if you were using a PCR test in order to prevent an outbreak.
If you have symptoms or were recently around someone with COVID, a positive result on an antigen test is usually correct, but a negative test result might not be right. If you just got infected, you may not have enough virus in your system for a rapid test to detect.
Once your virus levels have gone up, a rapid test will show a positive result.
If you have symptoms, it's best to take a second test 48 hours after the first. If you were exposed but don't have symptoms and test negative on both of those tests, it's best to take a third test 48 hours later.You can also get a lab test to confirm your result.
Be sure to follow all of the instructions that came with the test.
Antibodies are proteins created by your immune system to help you fight off infectious microbes. Your body makes them after you’ve been infected or vaccinated.
Antibody tests (also known as serology tests) look for antibodies to SARS-CoV-2 (the virus that causes COVID-19). They cannot be used to diagnose an active COVID-19 infection, because it can take up to three weeks after the infection for your immune system to make antibodies. These tests can only be used to determine whether someone had COVID-19 or a COVID-19 vaccine in the past.
The Food and Drug Administration (FDA) decides which drugs and medical tests can be used in this country. The full FDA approval process can take months to years.
When a public-health emergency happens, there isn’t time for new drugs or tests to go through the entire process. That’s when the FDA can use Emergency Use Authorization (EUA). It allows the FDA to let certain medical products be used more quickly, while still making sure they are as safe as possible. At a minimum, the product must have known and potential benefits that outweigh its known potential risks. In addition, there must be “no adequate, approved, and available alternatives” to the product receiving the EUA.
All treatments and tests for COVID used in the US have received an EUA - none of them have gone through the full approval process yet. The Pfizer and Moderna vaccines have received full approval from the FDA for adults. The Pfizer vaccine has an EUA for children ages 11 to 16.
Variants are mutated forms of SARS-CoV-2, the virus that causes the disease COVID-19. The variants that cause concern are ones whose mutations make them more likely to spread from person to person, cause more severe disease, and/or are able to more easily infect people who have been vaccinated.
All COVID-19 tests that have Emergency Use Authorization (EUA) from the FDA must be checked on an ongoing basis to make sure that they are able to detect different variants of the virus. If a test has any difficulty detecting a variant, the FDA must be notified immediately.
NOTE: As part of its calculations, the Workplace Testing Planner includes a default measurement of how transmissible the virus is. That measurement is called R0 (“R-naught”) or the basic reproduction number for the virus. WhenToTest.org follows CDC guidance to set the Planner's default for R0. If you would like to set a specific R0 in your scenarios, you can do so under Advanced Settings: Main Planner Settings.
R0 (R-naught) is a measure of the average number of people who will contract a contagious disease from one infected person. It’s a measure of viral transmissibility, or how fast the disease is spreading.
When R0 is exactly 1.0, it means that, on average, one infected person will infect one other person. When R0 is less than 1.0, it means that the spread of the disease is decreasing within the community. When R0 is above 1.0, the spread of disease is increasing. The more transmissible a disease or disease variant is, the higher its R0.
Prevalence is the percentage of people in a population who have a disease. So if there are 100 people in your area and 10 of them have COVID-19, the prevalence of COVID-19 in your area is 10%.
Technically, the only way to determine the true prevalence of COVID-19 in a population is to test every single person in the population to see who has it and who doesn't. Since that's not feasible, the Workplace Testing Planner and the COVID Risk Quiz use a sophisticated machine-learning model that looks at all of the available COVID-19 data for a particular state and county and develops a "predicted prevalence" for that location.
For US territories and areas outside the US, the Planner and the Quiz use a prevalence of 1% for typical conditions, and 3% for hotspot conditions.
Both the Workplace Testing Planner and the COVID Risk Quiz are based on CDC guidelines. Current guidelines define a “close contact” as someone who was within six feet of an infected person for a total of at least 15 minutes over the course of 24 hours. One exception to that rule is applicable only to schools: Students who were between three and six feet of an infected person are not considered close contacts as long as they were in school and “correctly and consistently” wearing masks.
All currently authorized COVID-19 vaccines are very good at keeping people from going to the hospital or dying from the virus. People who are up to date on their vaccines have the least risk of getting very sick, and they are are also less likely to get infected at all. Staying up to date on your vaccines is the most important thing you can do to protect yourself from COVID-19.
The type of mask you wear matters. Two-layer cloth masks have a filtration efficiency of about 30%. For surgical masks that fit well, without gaps, that number is about 70%. For KN95 masks, it’s about 85%.
You'll need to isolate. If you're at high risk of getting very sick from COVID-19, you should consider getting treatment.
Visit WhenToTest for up-to-date information on what to do when you test positive.
Yes. The Quiz uses an estimate of how well the vaccines available in the US protect against the variant that is currently dominant in the country. This estimate is based on the performance of all available vaccines, not on any one vaccine brand or type.
The COVID Risk Quiz takes information about how COVID-19 is behaving these days and combines that with information about your activities and your personal COVID-19 history. It then gives you an estimate of how likely it is that you might have COVID-19 right now.
The COVID Risk Quiz uses three basic kinds of information:
Data about COVID-19: This includes CDC reports on COVID-19 levels around the country and the latest research on how contagious COVID-19 is and how well the vaccines are working against it. It also includes how clean the air tends to be in different kinds of spaces.
Your COVID-19 history: This includes whether you’ve had it recently, your vaccination status, the kind of mask you generally wear, whether you have symptoms right now, and any known recent exposure to the virus.
Your behavior: This includes the kinds of places you go during a typical week and how often you go there, your mask-wearing habits, and any special events you attended last week or plan to attend in the near future.
The mathematical model behind the Quiz uses CDC data about local COVID-19 levels to figure out how likely it is that someone you meet in your area is infected. It converts that information into an estimate: If you had close contact with someone in your area, how likely is it that you would get COVID-19?
Next, the model looks at your COVID-19 history to see how well-protected you are against infection right now. The better-protected you are, the less likely it is that any one close contact will give you COVID-19.
Finally, the model converts your activities into an equivalent number of close contacts. Riskier activities are like having close contact with a lot of people. Less-risky activities are like having close contact with a smaller number of people.
The model then puts all the information together:
How many close-contact equivalents you’ve had over the past seven days.
How likely it is that any of those close-contact equivalents would infect you.
How well-protected you are.
The result is an estimate of how likely it is that you have COVID-19 right now.
Most people find out they have COVID by using rapid tests at home. If they don't tell their health care provider that they've tested positive, the case never gets reported to the CDC. Since that happens a lot, COVID case numbers around the country are often a lot higher than the the CDC's maps say they are. (The CDC knows about this problem, and the government is working on ways to solve it.) Some experts think that case numbers are about five times higher than what is reported, while others think they're as much as 20 times higher.
The COVID Risk Quiz deals with this issue by multiplying the COVID case numbers in a given county by seven.
The Planner and the Quiz have different goals and base their recommendations on different inputs.
The goal of the COVID Risk Quiz is to estimate your risk of having or getting COVID-19. It does that by taking information about how COVID-19 is behaving these days and combining that with information about your activities and your personal COVID-19 history. (This Quiz is a decision-support tool only. Results are provided for informational purposes and should not be construed as medical advice.)
The goal of the Workplace Testing Planner is to decrease the overall risk of an outbreak within a workplace or school. It does that by evaluating the COVID mitigation strategies in place at the organization and recommending the appropriate level of testing needed to complement those strategies.
You are in a COVID-19 hotspot if:
There have been at least 100 cases of COVID-19 per 100,000 people in your area over the past seven days, and/or
The test positivity rate in your area is currently 10% or higher.
The number of cases per 100,000 people is called the incidence rate. If you are outside the United States, you can find your country's seven-day incidence rate here.
If you are in a US territory other than Puerto Rico, you can find your territory's incidence rate on this map in the CDC's COVID Data Tracker. Puerto Rico is on the drop-down list of US states in the Planner itself.