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.