No, the average is nothing like 20%. It’s 40-60% effective each year: https://www.cdc.gov/flu/vaccines-work/effectiveness-studies.htm
You’re looking at the CDC, it depends on what and how many strains there are at the time. They are going to push flu vaccines, just like masks, shutting down the economy, etc.
Ask a doctor. My wife has been a nurse for 35 years.