https://www.theatlantic.com/health/archive/2020/03/how-will-coronavirus-end/608719/

“Second: duration of immunity. When people are infected by the milder human coronaviruses that cause cold-like symptoms, they remain immune for less than a year. By contrast, the few who were infected by the original SARS virus, which was far more severe, stayed immune for much longer. Assuming that SARS-CoV-2 lies somewhere in the middle, people who recover from their encounters might be protected for a couple of years. To confirm that, scientists will need to develop accurate serological tests, which look for the antibodies that confer immunity. They’ll also need to confirm that such antibodies actually stop people from catching or spreading the virus. If so, immune citizens can return to work, care for the vulnerable, and anchor the economy during bouts of social distancing.”