Assistant Professor of Molecular Medicine, University of Massachusetts Chen School of Medicine

Nathaniel Hafer received funding from the National Institutes of Health through UL1TR001453 and U54HL143541 awards.

The University of Massachusetts provides funding as a member of The Conversation US.

With the beginning of winter and the holidays in full swing, the COVID-19 pandemic has entered another worrying phase. The emergence of omicron variants and the increase in infection rates have made many people feel uncertain about their vacation plans.

On December 2, 2021, President Joe Biden outlined a series of actions in response to the COVID-19 pandemic, including making rapid COVID-19 testing at home eligible for private insurance reimbursement. As with vaccination, testing remains one of the most effective ways to track and reduce the spread of SARS-CoV-2 (the virus that causes COVID-19).

Although COVID-19 testing has become part of most people's daily conversations, many people still have questions about the difference between antigen testing and PCR testing, including when and how to use them.

I am a molecular biologist at UMass Chan School of Medicine. Since April 2020, I have been a member of a team called the RADx Tech project funded by the National Institutes of Health, which aims to help companies develop rapid tests to detect when a person has contracted COVID-19.

The rapid antigen test is designed to detect a portion of SARS-CoV-2 proteins (called antigens). First, use a cotton swab to take a sample from your nose or mouth as instructed. You mix the sample with the liquid that breaks down the virus. Then, you apply the liquid on the test paper, and the specific antibody against SARS-CoV-2 is drawn with thin lines on the test paper. Antibodies are Y-shaped proteins that can recognize and bind foreign substances such as antigens. If the antibody binds to the viral protein or antigen, a colored line will appear on the test strip, indicating the presence of SARS-CoV-2.

These tests are convenient because they are easy to use and can provide results quickly, usually within about 15 minutes. Another advantage is that the antigen test is relatively cheap, each test costs about 10 to 15 US dollars. In contrast, PCR tests usually require laboratory equipment and technicians, take 12 hours to several days to obtain results and cost $100 or more, although there are many ways to obtain these tests for free.

In his statement, President Biden also discussed a plan to distribute 50 million free tests to community healthcare providers for the uninsured. People should check the local media for information on when free rapid testing can be provided. In Colorado, families with school-age children have been able to undergo rapid testing for free for several months. Get ready to act quickly: In late November, 100,000 people in New Hampshire signed up for a free COVID antigen test in less than 24 hours.

As of early December 2021, the US Food and Drug Administration has approved about a dozen rapid antigen tests for SARS-CoV-2, which means that these tests meet certain performance and accuracy standards.

If you have any symptoms of COVID-19, regardless of whether you have been vaccinated or not, you should immediately undergo PCR or antigen testing.

Even if you have no symptoms, SARS-CoV-2 can spread easily. The sooner you can determine whether you have COVID-19, the sooner you can isolate yourself, which helps prevent spread to others. Early testing is also important, because new drugs like Merck and Pfizer work best if they are administered early in the infection process, shortly after symptoms appear.

If your antigen test result is negative but you still feel unwell, your test result may be false negative. Isolate yourself from others and contact your healthcare provider to discuss your symptoms. If your test result is positive, you should self-isolate at home and contact your healthcare provider as soon as possible.

If you have no symptoms but have been in close contact with a COVID-19 patient, what to do depends on your vaccine status. If you are fully vaccinated, the CDC currently recommends that you wait 5 to 7 days after exposure and then perform PCR or rapid antigen testing. If you are not fully vaccinated, get tested immediately. If you are not experiencing symptoms, you should still be retested 5 to 7 days after exposure.

Like many respiratory viruses, SARS-CoV-2 can take several days to accumulate in your body after exposure. In the early stages of infection, the amount of viral protein is relatively low, and rapid testing may not detect your infection. This is why it is recommended that many antigen tests be tested continuously over multiple days, with at least 24 hours between each test. When a person is infectious, rapid antigen testing is usually accurate because the amount of virus in the respiratory tract is the highest at this time.

Studies have shown that continuous antigen testing (usually performed 2 to 3 tests within a week) is equivalent to a single PCR test. Remember, the test is only a snapshot of your SARS-CoV-2 status at the time of the test. In the early stages of infection, it is possible, especially the antigen test, that the test result is negative.

Although our researchers have learned everything, there is more to know about the best way to use quick tests. Our team is conducting multiple studies to fill these gaps.

One question we are studying with a program called STOP COVID-19 is how people use home testing when their risk of infection is low and high. For example, a person who wears a mask indoors and does not eat in a restaurant may be considered low-risk, while a person who has not been vaccinated and does not wear a mask and gathers with many people is considered high-risk. We also want to know whether people will follow the testing protocol when they are exposed to the virus, and whether they will share their home test results with the local public health department.

Another major question that our team is investigating is: How does an antigen test compare to a PCR test when testing for COVID-19 in people who test positive but have no symptoms? An independent national study called "Test Us at Home" is generating important data that will help us answer this question in the coming months.

Rapid antigen testing is a popular tool for society to fight the COVID-19 pandemic. If used properly and combined with other tools (such as vaccinations, masks, and good hygiene), these measures will help limit the spread of SARS-CoV-2 during this holiday season.

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