Who is immune to COVID-19?

We’re not yet sure who is immune to COVID-19. So far, there is no scientific evidence to prove whether or not humans will be immune after they’ve been infected once. But our best guess is that most people who recover from COVID-19 will be protected from a second infection, at least for a while. Here’s the story behind that best guess.

The strength of a body’s immune response to a disease varies widely depending on which bug we’re talking about. After we recover from some diseases (like measles), our bodies mount a strong immune response that typically protects us for life. But for other diseases (like norovirus), we are only protected from re-infection for a few years. Although it’s less common, antibodies to some viruses (like dengue fever) can actually make us sicker if we’re infected again later. This is called antibody-dependent enhancement.

Studies of other coronaviruses give us some clues as to how our bodies might respond to this novel coronavirus. In one study, scientists exposed 15 volunteers to the common cold (a coronavirus strain called 229E). Ten of those volunteers became infected, and eight of them showed symptoms. The other five volunteers did not become infected. The same 15 people returned a year later to repeat the experiment. Some of the five previously non-infected people got infected in the second year, and a few of the ten previously infected people got infected again. But the infections were shorter and less severe the second time around. 

Antibody responses to viral infections also vary from person to person. Several factors can affect whether you develop antibodies after an infection. These include how sick you were, your age, and whether you have other health conditions. A study of 175 hospitalized COVID-19 patients showed that about half of them had a strong (“high” or “medium-high”) antibody response, but the other half had a weaker response. And the doctors didn’t find any protective antibodies in ten of the 175 recovered COVID patients.

So again, my best guess—based on what we know right now—is that most people who recover from COVID-19 will be protected from a second infection, at least for a while. My former professor recently wrote an op-ed and came to the same conclusion, so I hope that means I pass this epidemiology test.

Last updated: April, 24, 2020 at 2:30 pm

Science review: AGB, GSN