Again, generally correct.
A recovered patient is defined as recovered via 2 consecutive negative PCR tests 24 hrs apart. If those are the test results, Negative is the declaration. It takes more than 1 negative to be told to leave quarantine. Note this is only if there was a previous Positive.
A person that walks in with zero history and tests Negative is declared Negative. Only if Positive before that does it require 2 Negatives.
There are cases on record, not many but definitely not absurdly rare, where a Recovered patient leaves quarantine and is tested again a few weeks later and is Positive. The hope is he did not get re-infected. There is hope the swab is picking up viral segments from the original infection and not an active virus.
But . . . there are a few such cases that presented with symptoms. Those suggested re-infection and that’s very bad. It means immunity was short longevity.
Thanks for your thoughtful replies and explanations.
Regarding those who might be getting re-infected...
1. I’m sure there is a half-life or time-constant for the effectiveness of antibodies. They just don’t work at full strength for eight weeks and switch off. They must gradually diminish in effectiveness or in concentration. What is the probability distribution of half-lives of antibodies?
2. I wonder what the statistical distribution of the half-lives in the population is. Is it possible that some people experience a short period of immunity but others get much longer immunity? Is it possible those we see experiencing a short immunity period are corner-cases and most of the population would get one, two or more years of immunity? What is the probability distribution of immunity period?
3. We don’t get immune to the common cold or influenza because of the large number of pathogens and their rapid mutations. Is there any reason that won’t be the case with this CV?