For most of this year, the rolling average for the number of COVID-19 vaccinations administered each day in the U.S. has been trending downward. But that changed recently.

For eight consecutive days ending Friday, the last day for which data is available, the average number of vaccinations administered more than doubled to 485,505 a day Friday from 214,405 a day March 30, according to data from the Centers for Disease Control and Prevention.

The bulk of the recent vaccinations were booster doses, data shows.

While there is no certain explanation for the noticeable jump in shots, the daily increases came after federal regulators authorized second booster shots of the Pfizer and Moderna vaccines late last month for everyone 50 and older who had received their first booster shots at least four months earlier.

Those 12 and older with certain immune deficiencies were also authorized to receive a second booster, the Food and Drug Administration said.

More on the COVID-19 pandemic

Advertising

The decision meant that tens of millions of Americans have become eligible for their fourth vaccine shots just as the country is dealing with a highly contagious omicron subvariant, known as BA. 2, which caused cases to rise in Europe and which is now the dominant version of the virus in new U.S. cases.

Although caseloads nationally have been relatively low in recent weeks, BA. 2 is contributing to an increase in cases in some places, especially in the Northeast.

Public health researchers say it’s likely that older Americans seeking extra shots are driving the vaccination surge.

“Data from other countries currently experiencing BA. 2 surges suggests that second boosters will make a meaningful impact in protecting vulnerable individuals,” said Bertha Hidalgo, an associate professor of epidemiology at the University of Alabama at Birmingham.

After two years of living with the pandemic, the country’s campaign to vaccinate its population seemed to have hit a wall earlier this year, with fewer people showing up for first shots.

In at least 17 states, less than 60% of the population is fully vaccinated, meaning they have had two doses of the Pfizer or Moderna vaccines or had received the Johnson & Johnson single-dose vaccine. States where vaccinations lag include Alabama, Wyoming, Mississippi, Louisiana and Idaho, according to federal data.

Hidalgo said she did not expect to see an increase in vaccinations in states with low inoculation rates because of vaccine hesitancy — which, she added, was prevalent and persistent in many parts of the country.

“I do expect that numbers will largely plateau” in those states, she said.

More