In our collective efforts to prevent COVID-19 from spreading and overwhelming the health care system, we’ve seen evidence that social distancing is working.
Now, as the national conversation shifts to reopening, policy and medical leaders have made important progress on how we might ease social distancing restrictions safely.
Testing will play a pivotal role in our “return to normal.” Knowing which tests support what decisions – and knowing what COVID-19 testing can’t tell us at this point – will help us navigate the complex conversations ahead.
Reliable, accurate testing is critical
Testing has been a challenge in the United States and around the globe. Yet if we are to successfully ease restrictions, COVID-19 testing needs to be widely available and accurate.
Testing can show us how the disease moves through our communities and its pattern in populations. Testing can also help us understand whether immunity has developed, and if so, for how long it lasts. As we debate new measures aimed at getting people back to school and work, it’s important to have a sound understanding of how COVID-19 testing can and should guide decisions. For some, increased knowledge about testing serves as a defense against buying and using unreliable tests that don’t support quality decision making.
Two types of testing
As of today, there are two types of tests used for COVID-19: a nasal swab test that looks for infection, and a blood test that looks for antibodies.
Testing for infection
The nasal swab test is the best way to tell if someone is currently infected and can pass the virus to others. This test can be effective in helping to contain the spread of COVID-19 when it’s used as part of a test, trace, quarantine and track strategy. But for that to happen, testing needs to be widely available and reliable.
How it’s done: A swab is inserted through the nose or mouth to get a direct sample of mucous from the nasopharynx, the part of the upper respiratory tract sitting behind the nose and in the throat.
What it looks for: It looks for the RNA, or the genetic code of the virus, which is the best and earliest way to tell if someone is infected. The virus can be detected in the nose before antibodies can be detected in the blood.
How it can be used: To effectively stop the spread, the test must be part of a robust response plan that includes public health workers systematically tracing contacts of infected individuals and implementing isolation and quarantine restrictions on those who may have the virus and could spread it to others.
To make sure social distancing restrictions can be safely relaxed, the most immediate and important test-related challenges to be addressed include the availability of nasal swab testing, sample gathering logistics and test quality standards.
Testing for antibodies
The second type of test can confirm whether a person presently has COVID-19 or has recently recovered from it. This test will be valuable in helping us learn how immunity develops and how long it lasts after a person is exposed. Some refer to these antibody tests as serology tests because they are conducted on blood samples.
How it’s done: A blood sample is taken by finger prick or from a vein.
What it looks for: It looks for antibodies to the SARS-CoV-2 virus, which causes the COVID-19 illness. The presence of antibodies indicates that a person’s immune system has responded to fight off the illness, meaning they have COVID-19 or have had it before. The two types of antibodies produced, IgM and IgG, show up at different, overlapping times, and their presence lags behind the presence of the virus’s RNA in a person’s nose.
How it can be used: They’re important to knowing how many people have been infected. Over time it will give us a better understanding of how immunity to COVID-19 develops and how long it lasts.
IgM antibodies representing the body’s early response take at least a week to show up after someone’s been infected. IgG antibodies, on the other hand, represent the body’s more specific response to the virus. These antibodies show up about 20 days after the infection and are better indicator of a more durable and specific immunity to COVID-19.
Antibody tests are less useful as a tool for containing the spread of COVID-19 than nasal swabs because there is too much opportunity for an infected person to spread the virus before this test would identify it. What antibody tests can do, though, is help us tell how widely the illness has spread and how many people have recovered. Over time, this type of testing will help us better understand the true mortality rate of COVID-19, leading to a more informed health care system response. Eventually, antibody testing will also help us learn how long immunity lasts, possibly shedding light on how a vaccine may work.
We don't know what immunity means yet
There are certain things COVID-19 testing can’t tell us. And unfortunately, immunity is still an unknown – we simply don’t know yet whether the presence of antibodies means someone is immune to the disease, or how long that immunity might last.
Close relatives of this virus cause anywhere from 10 to 30 percent of the illnesses we call the common cold. While the immune response triggered by those viruses begins to fade away in as little as a year, it’s still too early to tell whether COVID-19 behaves similarly.
Due to the uncertainty surrounding immunity, the World Health Organization and Centers for Disease Control and Prevention have raised concerns about giving “immunity certificates or passports” to those who have recovered from COVID-19. Until we learn how long immunity lasts, there’s a chance previously infected people could contract the virus again and unknowingly spread it to others, especially if it’s assumed their safe. Another concern is that issuing immunity certificates may motivate people to catch the disease in hopes of recovering and having fewer restrictions. It could also make the testing problem worse by prompting people to buy unreliable tests in an effort to revive the economy more quickly using a test poorly suited to help with that.
While a return to life as we knew it may be months – if not years – away, our efforts to reduce social distancing restrictions can succeed if they’re executed thoughtfully. Knowing the differences between tests, the role each plays, and being forthright about what tests can and can’t tell us will make it easier for all of us to forge a coordinated and successful response to this pandemic.