[V]accines mimic a natural immune response, to the effect of developing long-term and in some cases lifelong immunity to reinfection.
The natural immune response to coronaviruses, however, is far more complex. Since the virus does have a well-documented ability to reinfect us, we can infer with reasonable confidence that natural immunity won’t defend us against it in the long term. Based on what we know about our immunity against COVID-19 and coronaviruses at large, there are three questions that developers of COVID-19 vaccines—and those of us who will be queuing up to receive them—must contemplate if we’re to create one that is safe, effective and protective for a long duration.
The first question is how long any immunity, whether natural or vaccine-mediated, will last. The second and more difficult question is whether a strong immune response can, in some, facilitate future infections, and if reinfection does occur, whether it might increase, rather than decrease, the amount of virus in the body.
The third and final question concerns the mechanisms by which coronaviruses reestablish infection in a person who has already been infected once before. One possibility is that they inactivate our memory cells—the equivalent of disconnecting the alarm. This is what the measles virus does upon first infection: target and kill memory B cells specifically. For now, whether this is the case for coronaviruses is unknown.