The purpose of this study is to learn about how well the yearly updates to the COVID-19 vaccine work in adults (age 18 years and above) with a healthy immune system (the body's cells, tissues and organs that work together to protect your body) and in children (age 6 months to 17 years). This study will use a collection of insurance claims and state vaccine registry data called HealthVerity. All patient names and other identifying information is removed. This study will include children who: * Are 6 months of age to 17 years of age * Are enrolled for at least 6 months in a row in a health insurance plan that provides data to HealthVerity * Are enrolled for at least 6 months in a row in a prescription drug insurance plan that provides data to HealthVerity * Live in the same US state for 6 months in a row * Live in a US state that requires COVID-19 vaccine reporting and provides all vaccine history data to HealthVerity * Do not have mismatches in sex and/or year of birth between any of the available datasets * Do not have records of having had COVID-19 and/or any COVID-19 vaccine in the 90 days before the start of the study This study will include adults who: * Are 18 years of age and older * Are enrolled for at least 12 months in a row in a health insurance plan that provides data to HealthVerity * Are enrolled for at least 12 months in a row in a prescription drug insurance plan that provides data to HealthVerity * Have lived in the same US state for at least 12 months * Live in a US state that requires COVID-19 reporting and provides all vaccine history data to HealthVerity * Do not have mismatches in sex and/or year of birth between any of the available datasets * Do not have records of having had COVID-19 and/or any COVID-19 vaccine in the 90 days before the start of the study This study will use the data that has already been collected, and no treatment or vaccine will be given in the study. People who match the information above will be followed in the HealthVerity database for up to 6 months following the first day that a new COVID-19 vaccine is available. This information will be reviewed to see if any of the following happen: * they had a COVID-19 vaccine * they're diagnosed with COVID-19 in a doctor's office * they visit the emergency department for COVID-19 * they visit urgent care for COVID-19 * they are hospitalized for COVID-19 The experiences of people who received a COVID-19 vaccine will be compared to the experiences of people who did not receive the vaccine. This will help to understand how well the Pfizer-BioNTech COVID-19 vaccine works at stopping COVID-19.