The promise of COVID-19 antibody testing
On Friday, Dr. Anthony Fauci, a leading public health expert and adviser to President Trump, announced on CNN that “within a week or so, we are going to have a relatively large number of tests” to determine if recovered COVID-19 patients, including those who never showed symptoms, have evidence of immunity. Among policymakers, there is discussion about whether results of this testing could be used to issue “certificates of immunity” that would allow individuals to return to normal life. Here are some of the key scientific considerations that will play into their conversations.
At this time, there is promising preliminary evidence that antibodies to SARS-CoV-2, the coronavirus that causes COVID-19 disease, will prevent reinfection. A recent study reported that five critically ill patients improved after receiving antibody-rich plasma from donors who had recovered from COVID-19. This potential treatment for COVID-19 is being further investigated with FDA guidance. Another study found that a subset of antibodies in 16 patients who had recovered from COVID-19 were able to neutralize, or prevent reinfection, with SARS-CoV-2. Given the small size of each of these studies, it is difficult to know if the findings will hold true at a population level. We do not yet know if all COVID-19 patients are able to mount effective immunity and prevent reinfection.
The important underlying concept is that not all antibodies can prevent infections. When we have an infection, our immune system will create many different antibodies. Some antibodies, called non-neutralizing antibodies, will attach to parts of the infectious agent, in this case SARS-CoV-2, that are not involved in how it invades our cells to cause disease. Think of non-neutralizing antibodies like an oven mitt on the wrong hand when you’re taking a tray out of the oven — useless for preventing a burn. At this time, it is not clear if every COVID-19 patient will develop neutralizing antibodies, or if only a subset will develop immunity that can prevent reinfection.
In China, Japan and South Korea, there are reports of COVID-19 patients who recovered completely, then developed new symptoms and tested positive for the virus a second time. It is not clear if these patients were reinfected or, more optimistically, if they had an unexplained increase in the virus, also called a reactivation, and symptom relapse. It’s also possible that some cases were false positives — the test was positive, but the patient did not have COVID-19. In South Korea, 51 patients from Daegu and the surrounding North Gyeongsang Province, the epicenters of the country’s COVID-19 outbreak, showed this pattern of recovery and then renewed symptoms. Jeong Eun-kyeong, director-general of the Korean Centers for Disease Control, publicly stated that it is likely due to reactivation, not reinfection. Additional data to put the matter to rest is not yet available, but a number of researchers are working to find answers.
Another open question with COVID-19 immunity is how long it will last. Other coronavirus strains that cause seasonal infections like the common cold, show declining immunity a few weeks after infection, and reinfection within a year. But SARS-CoV, the cause of the 2003 severe acute respiratory syndrome pandemic, has more genetic similarity to SARS-CoV-2 — and more reassuring immunity data. SARS patients had two to three years of protection from reinfection. If that is also true of COVID-19, it could buy the world enough time to develop and distribute a vaccine, which is probably at least 18 months off.
Immune testing for COVID-19 is inherently valuable. Widespread use will help us understand the extent of the virus’s spread in the population and can help identify individuals who are still vulnerable to infection.
The economic implications of “certificates of immunity” are highly appealing. Expedited research will help enable our leaders to make smart safe decisions for the well-being of all.
Ashita S. Batavia, MD, MSc, is a board-certified infectious disease specialist and public health expert with extensive experience in treating epidemics. She works at Lawrence Hospital NYP-Columbia. (Instagram: @ashita_batavia)
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