Thought of the case of the American sailors aboard the Roosevelt, assuming the report was true ...
13 USS Roosevelt Sailors Test Positive For COVID-19, Again
Soldiers tested positive for covid twice ... it could be explained ... several ways .... this was before the shots were being given ... so I excluded shot immunities from the equation.
- Natural immunities did not last. [Possible.]
- The sailors got such a mild, minor case (the first time), that no (or minimal) immunities were actually created. [Possible - seems unlikely.]
- The sailors got a false positive on one of the tests. [Possible - but unlikely.]
- There was more than one variant on the ship and some sailors got both variants. [Impossible to prove or disprove.]
- The virus may be capable of becoming dormant and later reactivating in some people's immune systems. [This sounds like a reach to me.]
...feel free to add some more ... these are the ones I have seen in print proposed.