Coronavirus tests are making headlines, but confusion remains. Different tests detect different things and have different uses. We walk through the two main types of tests related to SARS-CoV-2, the virus that causes COVID-19: what each test detects, how it detects it and what the test can tell us about current and prior infection.
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This nasal swab test detects bits of the virus itself and can tell you if you’re currently infected. Swabs are used to collect samples from the mucus membranes in the nose and throat where the virus may be growing or have been coughed up from the lungs. The assay used to detect the virus’ genetic material, RNA, is called the PCR assay.
If you’ve gotten a blood test, antibody test, or serology test, you’ve been tested for an immune response to SARS-CoV-2. This type of test uses a blood sample to detect specific immune proteins known as antibodies. These are found in the serum, the clear liquid that remains when clotting proteins and cells have been removed from blood. Our bodies make antibodies in response to infections, including coronaviruses. The ELISA assay is the most common method used to detect these antibodies.
While we produce antibodies to coronavirus during infection, antibodies to viruses also linger long after the infection has passed, which makes serology tests poor indicators of active infection. Additionally, most serology tests are designed detect a type of antibody that arises later during an infection, making them better at showing prior exposure.
What these type of antibody tests cannot do is show whether someone is protected from reinfection by SARS-CoV-2. A different type of test, which measures how well a person’s antibodies block infection by the novel coronavirus, gets closer to showing whether they’re protected or not.
And while the ELISA is a major type of serology test, it’s not the only one available. Several kinds of tests, including those that use technology similar to pregnancy tests, have hit the market, though not all give reliable results.
These tests detect viral proteins, or antigens, in a sample taken using a nasal swab. This type of test can detect an active infection much faster than the PCR test and doesn’t need a specialized lab to run. However, it’s a lot less accurate and more likely to return an inaccurate result. Inaccurate results are either a false negative, in which the test inaccurately suggests that someone who is infected with SARS-CoV-2 is virus-free, or a false positive, in which the test inaccurately suggests that someone who is actually uninfected is carrying the virus.
Tests for both active infection and prior exposure are being used as health officials and scientists grapple with the scope of the SARS-CoV-2 epidemic. Both will help us understand how far the virus has spread, who it affects and how much. The serology test is also used in studies looking at the potential therapeutic use of antibodies from those who have had COVID-19 and recovered.
The serology test will also help them determine whether most people mount a detectable immune response the novel coronavirus, as well as how long it lasts, key information needed to develop a protective vaccine.
But as the U.S. moves to reopen the economy and companies speed vaccine development, other tests must also come into play. A critical piece of information, which neither the swab test nor the basic serology test provide, is how well an immune response to SARS-CoV-2 protects against reinfection. Not all antibodies will neutralize, or block infection, by the novel coronavirus. Other tests that measure neutralization, like one being used by Moderna in their vaccine trial, will be to critical understanding whether a vaccine looks promising. They will also give us a better sense of how much we can rely on herd immunity to protect against later waves coronavirus infection. Currently there are no tests for neutralizing immunity available outside of a research setting.
This Fred Hutch research project is enrolling volunteers who are at high risk of being exposed to the novel coronavirus including health care workers, employees of long-term care facilities and hospitals, first responders, grocery store employees and bus drivers.
More than 30 U.S. cancer centers and organizations, including Fred Hutch and its clinical care partner Seattle Cancer Care Alliance, have come together to collect and disseminate data to better understand the scope and severity of COVID-19 in patients with cancer.
The Seattle Vaccine Trials Unit, part of Fred Hutchinson Cancer Research Center, is looking for people who are at risk for COVID or have tested positive for COVID-19 to take part in a research study. Individuals are needed to help us learn more about how the virus affects the immune system.