The initial Omicron variant of the SARS-CoV-2 virus and five groups of Omicron subvariants (BA.1, BA.2, BA.3, BA.4 and BA.5) can infect people who have been vaccinated against COVID-19. Fortunately, fully vaccinated people will generally experience only mild disease. To prevent serious disease and deaths, it is therefore critical that everyone who is eligible receives the recommended number of COVID-19 vaccine doses, especially those in high risk groups, including older adults.