Sorry, a bit technical. The CDC reports on the strains which are circulating in the US on a weekly basis.
Weekly U.S. Influenza Surveillance Report | CDC
It also provides information on which strains were in the vaccine used this year.
Frequently Asked Influenza (Flu) Questions: 2019-2020 Season | CDC
The standard and high dose shot had 4 strains included
Influenza A/Brisbane/02/2018 (H1N1)pdm09-like virus
influenza A/Kansas/14/2017 (H3N2)-like virus
Influenza B Colorado/06/2017-like (Victoria lineage) virus
Influenza B/Phuket/3073/2013-like (Yamagata lineage) virus
The circulating strains have been typed:
42 of 42 tested Flu A H1N1 are a good match to that in the vaccine
12 of 17 A H3N2 are a good match to that in the vaccine
19 of 25 B Victoria are a good match to that in the vaccine
10 of 10 B Yamagata are a good match to that in the vaccine.
So the CDC did a great job selecting the strains in this year's vaccine. There will always be more than 4 subtypes in circulation but they got the right subtype for each of the types.
It is important as well to note that when testing patients for influenza who have respiratory illnesses, only ~17% test positive nationally and 25% in
Florida. That means if you have respiratory symptoms it is far more likely that you do not have influenza.
The standard anti-influenza medications are excellent so far this year, the strains circulating are over 99% covered by the meds.
And just to make you worry, and encourage you to wash your hands... Influenza virus remains infectious for up to
several hours on a hard surface.
Lastly if you want to see a really terrific video showing how far droplets fly out of your nose and mouth when you sneeze... Check
THIS NPR video