People who are fully vaccinated do not need Covid-19 boosters, health and drug officials said Thursday.
"We are prepared for booster doses if and when the science demonstrates that they are needed," the Food and Drug Administration and the Centers for Disease Control and Prevention said in a joint statement.
The agencies said those who are vaccinated are protected from variants, including the surging delta variant. But they urged Americans 12 and older who have not yet been vaccinated to get their shots.
"People who are not vaccinated remain at risk. Virtually all Covid-19 hospitalizations and deaths are among those who are unvaccinated," the statement said.
The virus has killed more than 4 million people around the world in the year and a half since it was declared a pandemic. The U.S. leads the world with the highest reported death toll, at more than 600,000, followed by Brazil and India.
Pfizer said Thursday that it would seek U.S. authorization for a third dose of its vaccine, saying another shot within 12 months could dramatically boost immunity.
Research shows that two doses of mRNA vaccines offer strong protection against the highly contagious delta variant.
The U.S. agencies said they continue to study vaccines and possible boosters.
The FDA, the CDC and the National Institutes of Health "are engaged in a science-based, rigorous process to consider whether or when a booster might be necessary," the groups said in their statement. "This process takes into account laboratory data, clinical trial data, and cohort data — which can include data from specific pharmaceutical companies, but does not rely on those data exclusively. We continue to review any new data as it becomes available and will keep the public informed."
Among U.S. adults, 67 percent are at least partly vaccinated, and 47 percent of the total population is fully vaccinated.
President Joe Biden continues to push for more Americans to get vaccinated.
"We can't get complacent now," he said this week. "You can do this. Let's finish the job."
Biden has said his administration will shift its focus from mass vaccination sites to a smaller, more community-based approach to try to reach those still holding out on getting the shots.
The delta variant, which is more transmissible and has been linked to more severe illness in younger adults, is now the dominant strain in the U.S., the CDC said last week.
As of Saturday, it accounted for 51.7 percent of new Covid-19 cases that had been genetically sequenced in the country. Two weeks earlier, on June 19, the variant accounted for just more than 30 percent of new cases.