The COVID-19 crisis has changed everything about daily life in America – from economic upheaval to illness and infection to fear and anxiety in the face of the unknown. Complex and confusing information about COVID-19 tests adds to that anxiety.
Dr. Pat Courneya, chief health plan medical officer for HealthPartners, recently spoke with us to explain the various tests available for COVID-19, how they are being used to control the spread of the virus, and effective strategies to reopen cities and states.
What kinds of tests exist for COVID-19?
There are two types of tests currently used for COVID-19: a nasal swab test that looks for infection, and a blood test that looks for antibodies.
The nasal swab test tells doctors whether someone is currently infected with the virus and could pass it along to others. The blood test tells doctors whether someone had the virus before – which may indicate that they have some immunity to getting the virus again for some period of time.
How does the nasal swab test work?
The nasal swab test is the best tool for testing, tracing, isolating, and tracking the virus, so that we can contain its spread.
A swab is inserted through the nose or mouth to get a direct sample of mucous from the nasopharynx – that’s the part of the upper respiratory tract sitting behind the nose and in the throat. The test looks for the genetic code of the actual virus.
These tests are typically administered by a health care worker.
To effectively stop the spread of COVID-19, the nasal swab test must be part of a robust response plan. Public health workers should be equipped to systematically trace contacts of people who are infected and isolate them when appropriate.
Our most immediate challenges include getting enough tests to the right locations, gathering samples, and ensuring test accuracy. Turning around test results more quickly is also essential. And as we solve these challenges, we have to be sure to protect test accuracy. Across health care, we are all working together to resolve the challenges so we will be well positioned to safely begin easing social distancing restrictions.
What is the antibody test?
This test, commonly referred to as serology, can confirm whether a person currently has or has recently recovered from COVID-19. With this test, a medical professional takes a blood sample that looks for antibodies to the SARS-CoV-2 virus, which causes COVID-19. These antibodies represent the immune system’s effort to fight off the disease, and indicate the person has or recently had the illness.
There are two types of antibodies of importance here: IgM and IgG. They show up at different, overlapping times, and lag behind the detectable presence of the virus in a person’s nose. There are versions of the test that are specific for one or the other of the antibodies, and versions that test for both.
How is the antibody test used?
Over time, this test will help us understand how effectively we develop immunity and how long that immunity lasts. It will also help us understand the total prevalence of the virus even among people who did not experience symptoms.
The time it takes for antibodies to develop is the biggest reason serology tests are less useful in containing the spread of disease. There is too much opportunity for an infected person to spread the virus to others before this test would identify it. IgM antibodies, which represent the body’s early and less specific response to the illness, take at least a week to show up after a person’s been infected. IgG antibodies show up on average 20 days after infection and represent the body’s more specific response to the virus. The latter is a better indicator of a more durable and specific immunity to COVID-19.
Serology tests will help us better understand the true mortality rate and have a more-informed health care system response. With time, as this type of testing helps us understand how long the immunity lasts, it may also give us important insight into how a vaccine may work.
The FDA has also said that antibody tests can help in determining who may qualify to donate blood that can be used to create convalescent plasma, which may be a potential treatment for individuals with severe cases of COVID-19. Limited data indicate that convalescent plasma may help COVID-19 patients and active research is underway to validate that early impression.
How accurate are the antibody tests?
Unfortunately, we don’t know yet how well COVID-19 serology tests indicate immunity to the disease, or how long the immunity might last. Close relatives of this virus circulate widely and cause 10-30% of the illnesses that we think of as the common cold. Those viruses trigger an immune protection that fades away after just one year. It’s too early in the course of our learning about COVID-19 to know if it behaves similarly.
Because of these uncertainties, the World Health Organization and Centers for Disease Control and Prevention have raised concerns about using so-called immunity certificates to reduce social distancing restrictions.
Not all marketed serological test have been evaluated by the FDA or had their accuracy validated. It is important to know that those tests approved under an Emergency Use Authorization have not gone through full FDA review.
How important is COVID-19 testing?
The widespread availability of accurate COVID-19 diagnostic testing is fundamental to easing restrictions and must be coupled with contact tracing. Having reliable tests, and a sound understanding of what these tests indicate, is critical as we determine when to safely relax social restrictions, expand availability for non-COVID care and get people back to work.
Antibody testing is necessary to understand the disease’s movement in our communities, its pattern in populations, and the development and duration of immunity for those who have recovered.
However, full population testing should not be the goal for either the nasal swab test or the antibody test. For the nasal swab test, checking symptomatic patients and checking contacts can help us control the spread of the disease. For antibody testing, an important strategy is to test a statistically significant sample at intervals to make good estimates of the spread of the disease and the percentage of the population that has recovered from COVID-19.
Testing is constantly evolving to keep up with the latest scientific breakthroughs, and it will be critical to keep monitoring the space as the fight against COVID-19 continues.