(Bloomberg) -- U.S. cases and deaths dropped further, in a week when Covid-19 vaccinations ticked up slightly after weeks of declining. At least one dose has been administered to 52% of all Americans, according to the Bloomberg Vaccine Tracker. British Prime Minister Boris Johnson said he is now less optimistic about the U.K.’s pandemic outlook, suggesting restrictions may need to be kept in place beyond his target date for relaxing the rules on...