 This study found that two doses of either BNT162B2 mRNA or mRNA1273 provided high levels of protection against SARS-CoV-2 infection and COVID-19 hospitalization with the alpha and delta variants. Additionally, the third dose of either vaccine significantly increased the level and duration of protection against SARS-CoV-2 infection with the Omicron variant and provided a high level of sustained protection against COVID-19 hospitalization among those aged 60 years or older. This article was authored by Mia Adjermos-Gram, Hanna Dorthenborg, Astrid Blitzer-Sheld and others.