More than half of all adults have received at least one dose of SARS-CoV-2 vaccine, and one-third are fully vaccinated. A total of 132 million individuals have received at least 1 dose of the vaccine, equivalent to 40% of the entire US population and 51% of all adults. Of those, 85 million (26% of the total population; 33% of adults) are fully vaccinated. Among adults aged 65 years and older, 80% have received at least 1 dose, and 65% are fully vaccinated. In terms of full vaccination, 42 million individuals have received the Pfizer-BioNTech vaccine, 35 million have received the Moderna vaccine, and 7.9 million have received the J&J-Janssen vaccine. As of April 19, all US states have expanded COVID-19 vaccine eligibility to include all individuals age 16 and older. With vaccination rates continuing to climb in the United States, many who are vaccinated are beginning to engage in more activities that could increase their exposure to SARS-CoV-2 infection. While the vaccines available under US FDA Emergency Use Authorizations are effective, there is still a chance that vaccinated persons can become infected with SARS-CoV-2. These “breakthrough” infections are considered rare events, with the CDC on April 19 reporting fewer than 6,000 cases out of 84 million vaccinated persons. The agency continues to monitor reports of breakthrough cases and launched a website with information for public health departments and laboratories to investigate and report such cases. The agency is monitoring the age, sex, type of vaccine, and underlying conditions from breakthrough cases, but no pattern among cases has been identified. When possible, monitoring also includes genomic sequencing to identify which virus lineage caused the infection.