They are when there's little quantitative data to work with.
A lot of people's biggest questions are what the hell "COVID-19 symptoms" and apparently it means just about anything.
I'm suspicious of the 2 week long illness my family has just gotten over. Hit each of us differently. Predominantly nasal mucus, but the kids had some chest congestion, wife had a fever, and I had what felt like a sinus infection and a bit of a dry cough.
None of it particularly severe. Likely not COVID-19, but given the scattershot presentation of the disease in non-critical cases, I'm not ruling it out.
We don’t have sufficient data because we are, in our infinite wisdom, not testing every person with a pulse. Or at least testing from as random of a population subset as we can manage. At least in the US. Other countries mileage may vary.
But even then it is my understanding that there currently is no way to test if you already had it.
