The Omicron variant of SARS-CoV-2 is much more effective at infecting people vaccinated against the COVID-19 disease it causes, a review of research on the subject suggests. Research also indicates vaccination provides less protection against serious disease upon Omicron infection. The Omicron variant, first detected in South Africa in November, now constitutes the dominant strain in the United States, according to estimates by the Centers for Disease Control and Prevention (CDC). It comprised about 31-45 percent of infections in the week ending Dec. 18, according to the latest CDC variant surveillance data. In the week ending Jan. 1, it was already 93-97 percent, the agency projected. Omicron appears to spread more easily, but with less severe symptoms. A recent Danish study found that a fully vaccinated individual in an Omicron-infected household was about as susceptible to get infected as an unvaccinated individual. Boosted individuals were about half as susceptible. That’s …