On the issue of reinfection, reactivation and persistent infection
There have been reports of people in our community who appear to have had COVID in the past (evidenced by antibody presence, viral test, or classic symptoms) and have since recovered for many weeks, and who now have covid-like symptoms again. Some of these individuals are now testing positive for the virus. What does this mean; how do we interpret this?
There are several possibilities:
1. Their body had completely fought off the virus, and then they caught the virus again from someone else, resulting in the second set of symptoms.
This is the most worrisome possibility, and what people typically mean when they say “reinfection”. These people lend credence to the possibility that protection acquired from the original infection is indeed short lived (as witnessed by IgG antibody levels falling quite rapidly as we see), and that given a sufficient exposure to another infectious individual, they may become reinfected and sick with COVID all over again, and may themselves be infectious. They would need to quarantine fully for at least 10 days after the onset of symptoms, just in case this truly is a new infection (even if they have antibodies).
2. Their body did not completely fight off the virus; some virus remained dormant. That remaining virus was somehow reactivated, causing those second set of symptoms.
This is less worrisome, as it does not necessarily imply community spread. As of this time we have tended to think of people who have the virus as not being infectious 2 weeks after symptom onset. Whether patients with “reactivated infection” truly exist, or this is either option 1 above or 3 below remains to be proven.
3. Their body completely fought off the virus, but some viral particles remained in their secretions for many weeks, presumably dead/inactive. Their second set of symptoms was in fact not due to active infection with coronavirus but possibly is a delayed immune response or other infectious cause, however when tested for the virus, the test sensed those remaining viral particles and returned a positive result.
This is the least worrisome, although there is a limit to how long we think dead viral particles hang around for.
In addition, if they had tested negative for the virus (twice ideally) while they were recovered, and then the test turned positive on their second set of symptoms, this option is no longer a reasonable consideration.
Which one of these possibilities is the true answer, or indeed whether the true answer is a combination of these three possibilities, is still unknown. This is currently one of the most pressing questions about the virus, and one which is being actively researched.
A somewhat related question is how long antibodies last for. Meaning, even if we assume that someone who interacted with the virus indeed does have protection, we are still studying how long that lasts for, and whether the antibodies are the sole measure of this protection, or does immunity possibly rest elsewhere in a profoundly complex human immune system (and not necessarily dependent on antibody levels). Again, this is something being studied, and we hope that for the majority of people protection lasts at least several months and more.
Practically:
If someone already had covid (by antibodies, viral test, or classic covid symptoms) and is now experiencing a second set of typical covid-like symptoms, please do get tested for the virus. If the test is positive, please isolate yourself until 10 days have elapsed from the beginning of the symptoms and your fever/symptoms have resolved.
If someone already had covid (by antibodies, viral test, or classic covid symptoms) and then later has a positive viral test but is not having any covid symptoms, they do not need to quarantine, however they should be very careful with mask use and social distancing.