Vaccine effort complicated by need to balance scarce first and second doses.

US vaccine drive complicated by 1st, 2nd dose juggling act The U.S. has entered a tricky phase of the COVID-19 vaccination effort as providers try to ramp up the number of people getting first shots while also ensuring a growing number of others get... AP NEWS

The U.S. has entered a tricky phase of the COVID-19 vaccination effort as providers try to ramp up the number of people getting first shots while also ensuring a growing number of others get second doses just when millions more Americans are becoming eligible to receive vaccines.

The need to give each person two doses a few weeks apart vastly complicates the country’s biggest-ever vaccination campaign. And persistent uncertainty about future vaccine supplies fuels worries that some people will not be able to get their second shots in time.

In some cases, local health departments and providers have said they must temporarily curb or even cancel appointments for first doses to ensure there are enough second doses for people who need them...

For about the past month, the U.S. has administered an average of 900,000 first doses each day, according to data from the Centers for Disease Control and Prevention analyzed by The Associated Press. Now many of those people are due for second doses, and the average number of Americans getting second shots hit an all-time high Tuesday — 539,000 per day over the past week.