Omicron less severe than Delta but more easily evades boosters

Three new observational studies from Scotland, Denmark, and the United States detail reduced hospitalizations and emergency department (ED) visits for Omicron COVID-19 infections relative to those caused by the Delta variant, as well as strong but waning third-dose vaccine effectiveness over time against Omicron. Two-thirds reduction in hospitalizations In Scotland, a team led by University of Edinburgh researchers conducted a test-negative case-control study of national COVID-19 infections among residents from Nov 1 to Dec 19, 2021, to estimate effectiveness of a third vaccine dose against symptomatic illness relative to that 25 weeks or more after receipt of the second dose. The study was published late last week in The Lancet Infectious Diseases. By study end, 23,840 Omicron infections were reported, primarily among those 20 to 39 years old (49.2%). The proportion of possible Omicron reinfections was more than 10 times that of Delta cases (7.6% vs 0.7%). Fifteen patients infected with Omicron were hospitalized,...