Greetings! There is a new CDC Guidance updated on Monday August 23, 2021, that provides a good explanation of breakthrough infections of Covid-19 variants in people who are fully vaccinated. This guidance also reiterates the CDC recent recommendations on mitigation methods for fully vaccinated people, and discusses immunocompromised people. https://www.cdc.gov/coronavirus/2019-ncov/vaccines/effectiveness/why-measure... It may be of use to libraries in determining COVID-19 policies and procedures. Take Care! Clare