The two most preferred COVID-19 vaccines in the United States are much less effective against the Omicron virus variant, a trio of new studies out Friday found. The effectiveness of two doses of the Pfizer and Moderna COVID-19 vaccines dropped dramatically against both infection and hospitalization after Omicron became dominant in the United States late last year, researchers with the Centers for Disease Control and Prevention (CDC) and other health institutions said in one of the studies. Drawing from records from institutions in 10 states between August 2021 and January, the researchers estimated that effectiveness within six months of dose two against emergency room and urgent care visits plummeted from 86 percent during the wave driven by the Delta variant to 52 percent during the Omicron-driven wave. That protection dropped even further among those who got their second dose over six months prior, from 76 percent during the Delta dominance …