Bivalent Covid booster doses updated for Omicron were just authorized in the US and are already starting to become available: 

https://www.cnn.com/2022/09/01/health/covid-omicron-booster-explainer-wellness/index.html

Resolves to the percentage of the US population that has been vaccinated with a bivalent Covid booster dose at the end of October. (Percentage of the total US population, not just the eligible US population.) Resolution will be based on CDC (this page 

https://covid.cdc.gov/covid-data-tracker/#vaccinations_vacc-people-additional-dose-totalpop

 currently shows several different vaccination stats and will likely add data for bivalent doses in the near future). If data is not available from the CDC, then resolves based on another official source.