At least 7.6 million people have received an updated Covid booster since the start of September, according to data released Thursday by the Centers for Disease Control and Prevention. That number represents around 3.6% of people currently eligible to receive the shots in the U.S.
The data does not include people who received updated Pfizer-BioNTech boosters in Idaho and Texas, the CDC said, so it is likely an underestimate.
The CDC signed off on updated versions of Pfizer’s and Moderna’s booster shots on Sept. 1, and pharmacies and other vaccination sites began administering the new shots around Labor Day weekend. The bivalent shots target both the original coronavirus strain and the currently circulating omicron subvariants BA.4 and BA.5.
Dr. Scott Roberts, a Yale Medicine infectious disease specialist, said the relatively low booster uptake was "demoralizing."
"I would expect a much higher proportion of Americans to have gotten the booster by this point," he said.
Roberts said a lack of public awareness about the shots or the prevailing narrative that the pandemic is ending might have hindered the vaccine rollout.
"The fact that this booster came out days before Biden said the pandemic is over is a huge mixed message," he said. "Now it’s going to be that much harder to convince those at risk who are on the fence to get a booster."
Still, the U.S. has seen an uptick in demand for Covid shots since the booster rollout began: The U.S. is currently administering around 356,000 Covid vaccine doses per day, as a weekly average. That's more than triple the number from the start of the month.
As of last week, the U.S. had shipped more than 25 million bivalent booster doses to tens of thousands of sites. The vast majority of the population now lives within 5 miles of a site offering the updated vaccines.
The CDC recommends that everyone over 12 get an updated booster, as long as at least two months have passed since their last Covid shot. People who recently got Covid should wait at least until their acute illness is over, and the CDC says they can consider delaying their boosters until three months after their symptoms started or since they first tested positive.
People can mix and match vaccines from Pfizer and Moderna, but Pfizer’s updated booster is available to people ages 12 and up while Moderna’s is limited to ages 18 and up.
Some pharmacies reported shortages of Moderna's updated booster earlier this month. But CVS said on Friday that it had started to receive additional Moderna doses and expects more over the coming days and weeks. Walgreens said the availability of Moderna doses varies by location.
Nearly 80% of the U.S. population has received at least one shot of a primary Covid vaccine, and nearly 68% is considered fully vaccinated by the CDC, meaning they've gotten either one dose of the Johnson & Johnson vaccine or two shots of Pfizer's, Moderna's or Novavax's, which was authorized in July.
Biden administration officials have pointed to the updated boosters, however, as a critical step to pushing the U.S. out of the pandemic.
"For the first time since December of 2020, these vaccines, our vaccines, have caught up with the virus," White House Covid-19 Response Coordinator Ashish Jha said at a briefing earlier this month.
Jha said the shots should provide better protection against infection and transmission, as well as more lasting protection against severe illness, compared to earlier Covid vaccines.
But experts are still gathering real-world data, since the shots were distributed without results from human trials. Laboratory studies found that the boosters generated strong antibody responses against BA.4 and BA.5, and human trial data showed that a similar vaccine yielded a strong antibody response against the initial omicron strain, BA.1.
Authorization of the bivalent boosters for children ages 5 to 11 may be just weeks away, Dr. Peter Marks, director of the Food and Drug Administration’s Center for Biologics Evaluation and Research, said at an event this week with the Covid-19 Vaccine Education and Equity Project.
Public health officials expect to see another Covid wave around Thanksgiving, and flu season tends to pick up in October, so the CDC says the updated Covid boosters and flu shots can be given together.
If the pace of booster vaccinations doesn’t pick up, Roberts said, the U.S. could see an increase in cases, hospitalizations and deaths.
"Many people are certainly due for a booster and this comes at a critical time," he said. "We’re going into the winter season when we expect cases to go up. Many areas around the country right now are continuing to have high levels of circulating virus."