Genetic sequencing of COVID-19 in China in December 2019 revealed two strains of the virus, identified as S and L, with S being the ancestral version while L was more prevalent (70:30 ratio) and more virulent.
In December, I and all my family (in the UK) experienced a viral illness of severity somewhere between a cold and influenza, which we all independently declared was strikingly different in character to any cold or flu we had previously experienced. We experienced mild headaches, mild bodily aches and a dry cough. Notably it really dragged on, for three weeks or possibly more. My fit and healthy mum (aged around 70) suffered fairly severe respiratory distress (not so severe she required hospitalisation) and we were quite worried about her.
Fast forward to now, and this experience obviously takes on a new perspective. What can we say about the probability this illness was some coronavirus (not necessarily COVID-19)? What's the likelihood it was one of the two strains of COVID-19? Do we know, or can we estimate the likelihood, that any antibodies to any given coronavirus confer some immunity to other strains?
What I do know of this, is that there are known cases of people becoming ill again with COVID-19, having earlier been declared virus free - it's unknown whether they caught one strain then the other, or became reinfected with the same one twice, or the virus increased in activity again.