We are the host of the virus that carries the covid disease. We spread it. When we talk closely to people. Its not only in the air. Its also not as easy to control 8 billion people compare to 1 billion people. Its harder to eradicate disease as the population grows.
Spainish flu was 100 years ago. The population of the world was like 2 billion. And the spainish flu is not the same virus as covid. You cant compare the 2 pandemics.
No its not possible because we all have different DNA or RNA. All viruses or bacteria will differ. Yeah there could be false positives or negatives in PCR