The effect of influenza vaccination on trained immunity: impact on COVID-19 | medRxiv
https://www.medrxiv.org/content/10.1101/2020.10.14.20212498v1

> Hospital workers who got vaccinated were significantly less likely to develop COVID than those who did not

I believe that is just a simple sampling problem. People had flu shot this year because they're really careful about infectious diseases. They maybe also sanitize more.

medRxiv

The effect of influenza vaccination on trained immunity: impact on COVID-19

Every year, influenza causes 290.000 to 650.000 deaths worldwide and vaccination is encouraged to prevent infection in high-risk individuals. Interestingly, cross-protective effects of vaccination against heterologous infections have been reported, and long…