Giving 1st and 2nd doses at once complicates vaccine effort

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.

After getting her first COVID-19 vaccine shot, Sarah Bouse was told she would be notified to set up the second. But the notice never came, and she frantically called the Houston Health Department to schedule the booster the evening before it was due.

“It was frustrating — the waiting game and the conflicting information,” said Bouse, who is 26 and eligible because of a health condition. After hours on the phone, she finally got through to someone and scheduled the shot.

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 states are trying to administer first doses to an expanded pool of recipients.

“It’s really important and critical to recognize that there are still not enough doses to go around,” said Dr. Nirav Shah, director of the Maine Center for Disease Control and Prevention.

So far, about 10% of the U.S....