The U.K. reported the highest number of daily Covid-19 cases since the pandemic began on Wednesday and experts believe omicron could already be the dominant variant in London.
The mRNA shots were around 20% effective at preventing infection with delta in males over age 65 months five through seven after completing vaccination.
Early studies suggest an initial vaccine series provides little protection against infection from omicron—but is still effective against severe disease—and a booster shot is necessary for higher levels of immunity.