One of the big unanswered questions is whether someone is immune to reinfection with COVID-19 after they’ve recovered from a positive case. The current thought is that people are most likely immune. But what is the evidence? Unfortunately, it is still not a confirmed finding.
There was a recent report giving some information about four cases in Wuhan China where the individuals initially tested positive for COVID-19 and then recovered. A follow-up test after recovery was negative, but then another later test returned a positive result.
The main (optimistic) theory is that these are not new infections. The thought is that these people were infected, but when retested after symptom recovery, the negative test was inaccurate, i.e., a false negative. Then, when they were tested a 3rd time, they were positive because they had never really been negative.
Also in that report, they mentioned:
In February, Wang Chen, a director at the state-run Chinese Academy of Medical Sciences, estimated that the nucleic acid tests used in China were accurate at identifying positive cases of the coronavirus only 30%-50% of the time.
If accurate, that statistic is pretty scary. It would mean that 50-70% of positive cases were missed. While that would support the idea that there were false negatives in the cases where people appeared to recovery but then later tested positive, it does not bode well for us accurately identifying cases and isolating people who may be contagious.
I will try to update this post as we have more information. Maybe once we do more widespread antibody testing we will have a better idea of who is actually recovered and no longer contagious. Hopefully the current optimistic idea of long term immunity after exposure winds up being true.