We are still learning a lot about what kind of immunity a person has after being infected with COVID-19, and how long that immunity lasts. A a small number of people have reportedly become reinfected with virus following an initial infection and research is ongoing. According to the US Centers fo Disease Control and Prevention (CDC), "reinfection means a person was infected (got sick) once, recovered, and then later became infected again. Based on what we know from similar viruses, some reinfections are expected. We are still learning more about COVID-19."
In a press conference on December 4th, 2020, the World Health Organization acknowledged emerging evidence that suggests that COVID-19 immunity is unlikely to be lifelong, which suggests reinfection may be possible.
The most reliable way to measure immunity to COVID-19 is unclear, and, whether from infection or vaccination, scientists still do not know how long immunity to COVID-19 may last.
Though reinfection has been documented, there are many ongoing questions about whether or not reinfection poses an ongoing risk, how common it is, and what kind of immunity to the virus people might obtain once they have been infected. Currently researchers believe that most people will be protected from reinfection for up to six months following infection, but research is ongoing.
There are multiple pre-print studies with large participant groups that suggest immunity does last for up to six months but decreases over time. Antibodies decrease more quickly in young adults who have had an asymptomatic infection.
Pre-print studies have also suggested that reinfection is possible. It is important to note that there is a shortage of peer-reviewed papers (so other scientific experts are not yet able to rigorously study the data or full results). It is also important to note that antibody levels may not be a strong indicator of immunity against the virus and likelihood of reinfection.
To prevent infection, reinfection, and spread of COVID-19, experts recommend frequent hand washing, social distancing (6 feet/2 meters apart), avoidance of crowded areas (especially indoors), wearing a face mask (though the U.S. CDC now suggests wearing a cloth mask over a surgical mask or a high grade respirator), and staying home when you are sick or know that you have been exposed to COVID-19.