Oh, my mistake. I've corrected it from 'up to' to 'down to' 0.3 microns, so thanks a lot for pointing that out. (I'm not sure if I have written anything about 2.5 microns though.)

You are also right that a single SARS-CoV-2 virion is in the nano scale (50-200 nanometer or 0.05 to 0.2 micron). However, SARS-CoV-2 is transmitted via aerosols, and an aerosol particle contains more than one SARS-CoV-2 virion, making its size about 5 microns.