Public health officials have cautioned in recent days that antibody testing isn’t a “silver bullet” to discovering immunity to COVID-19. In a scientific brief issued Friday, the World Health Organization warned that people who have recovered from the coronavirus are not necessarily protected from catching the disease again. “There is no evidence yet that people who have had Covid-19 will not get a second infection," the brief says.
Though it isn’t wise to use antibody, or serological, tests as a sole measure of determining when it’s safe to reopen the economy, several methodologies are currently under evaluation at VUMC to potentially get us closer to understanding the relationship between seropositivity—the positive presence of an antibody—and immunity.
“We anticipate offering serologic testing for select patient populations in the near future,” said David Aronoff, MD, Addison B. Scoville Chair in Medicine and Director of the Division of Infectious Diseases, “although all of the relevant details have not yet been determined due to the dynamic nature of the situation.”
For the latest perspective on the value of COVID-19 antibody testing, read on for more of Dr. Aronoff’s answers to common questions.
What is antibody, or serologic, testing?
After suffering from an infection, the body typically develops an antibody response to the particular pathogen that caused it. A serological test can detect these antibodies in the blood and can traditionally measure whether a person has been infected with that pathogen.
There are many unknowns about antibody tests for COVID-19. What can a positive serology test tell us—and not tell us—about COVID-19?
Two of the major benefits of measuring antibodies to the COVID-19 virus is to 1) confirm to an individual that they have been infected with this virus in the past and 2) understand how many people in a population have already been infected. A third potential benefit is that someday we hope to know whether the presence of antibodies against COVID-19 means that person won’t getting re-infected with the same virus or related viruses.
Unfortunately, right now we don’t yet know for certain whether COVID-19 antibodies indicate immunity. Although it is likely that infection does impart some degree of protection from future reinfection, we do not know how complete or durable the immune response is. With time, we will learn more about whether a recovered patient is susceptible to reinfection and how mild or severe such an infection might be.
What testing is being developed for the detection of COVID-19 antibodies?
Various laboratory methods are being developed to detect COVID-19 antibodies. However, the rapid emergence of the virus means some tests aren’t undergoing the same degree of rigor that diagnostic tests are typically subjected to in the United States before they enter clinical care.
The FDA has authorized a small but growing number of tests to be used for emergency care, and presently all serologic testing for patient care in the United States is required to be performed in accredited clinical laboratory environments. However, many other tests are being introduced to the commercial market without passing stringent clinical and analytical validation.
What are the potential limitations of serologic testing?
In addition to the key question of whether COVID-19 antibodies signal immunity, serological testing also presents additional uncertainties. For the so-called “rapid” serologic tests flooding the market, the World Health Organization currently recommends that such tests only be utilized for research purposes, not clinical decision-making. That’s because:
- False-positive results can occur. It is possible for a serologic test to yield a “positive” result even if a person has never been infected with COVID-19. Occasionally, a person may possess antibodies directed against one microbe, but that cross-react during serologic tests for different pathogens. Additional research is needed to determine what percentage of non-infected individuals might possess cross-reactive antibodies that could lead to these false-positive results.
- False-negative tests can occur. Even in a patient with a documented history of COVID-19 infection, it is possible for their blood not to generate a strong enough signal for a positive serology result. For instance, if a patient cannot generate a robust antibody response due to a suppressed immune system, these false-negative results can occur. Even in healthy people, the strength and duration of the antibody response can vary for different pathogens and between individuals. If a person recovers from infection but does not have measurable antibodies in their blood, that may or may not reflect their risk for reinfection.
What’s the danger of even a small percentage of false-negative or false-positive results?
Getting bad data can be confusing and harmful because it gives people a false sense of security. The wrong kind of information can even be dangerous.
Even though we're in the throes of a pandemic, we have to allow time to establish the accuracy and validity of tests before we officially roll things out, especially when lots of potentially invalid tests are being pushed onto the market. VUMC’s cross-departmental COVID-19 serology team—made up of experts in pathology, microbiology, immunology and infectious disease—are working closely with commercial vendors that manufacture tests for detecting these antibodies and are in the process of validating those in our accredited lab. The goal is that when Vanderbilt tells patients that they have or haven’t had COVID-19 infection, that the data is as valid as possible.
We will have answers to all these questions in time, but we can’t make assumptions right out of the gate.
How is VUMC learning from other medical systems in the United States and abroad to help deal with the pandemic?
We're definitely learning a lot from our colleagues around the world, and we’ve been involved in frequent conversations with leaders in infectious diseases all around the United States, learning from them about their experiences and how they're managing patients. It’s been a very good way for us in infectious diseases to support each other, and the same is happening across all disciplines of medicine and nursing that are dealing with this pandemic.
Please join us virtually on Thursday, May 7, from 1–2 p.m. CDT, for a webinar on
Back-to-Work Safety for Employers
The webinar will feature insights and expert perspective from
VUMC’s David Aronoff, MD, Addison B. Scoville Chair in Medicine and
Director of the Division of Infectious Diseases.
