Federal regulators authorized second booster shots of the Pfizer-BioNTech and Moderna coronaviruses vaccines for everyone 50 and older on Tuesday, describing the move as an effort to bolster waning immunity against severe disease in case the virus sweeps the nation again in the coming months.
People in the age group can get the additional shot at least four months after their first booster. The agency approved a second booster for people with certain immune deficiencies.
The decision means that tens of millions of Americans are eligible for a fourth shot. Even though the public may be tiring of repeated doses, the move is most likely an interim one: Federal health officials say it is quite possible that Americans of all ages may need another shot in the fall to prepare for any winter surge. The hope is that by then, scientists will be able to modify the existing vaccines to work better and last longer against the new ones.
Federal health officials considered limiting second boosters to people older than 60 years old. A lower age limit would make sense because so many Americans over 50 have chronic medical conditions that put them at risk, said Dr. Peter Marks, who oversees the F.D.A.'s vaccine division.
While a single booster dose continues to protect most Americans from hospitalization and death due to Covid-19, he said, those 50 or older who got their first booster more than four months ago should seriously consider getting another.
The Centers for Disease Control and Prevention was a bit more circumspect. When the first round of boosters was approved, the agency said there was a clear benefit.
The C.D.C. updated its vaccine guidance on Tuesday to say that second boosters are now allowed. The director of the agency said that the option of another dose was especially important for those 65 and older and those 50 and older with underlying medical conditions that increase their risk for severe disease from Covid-19.
The decision was made largely from Israel. There is a need for stronger protection now that the vaccines have been altered. There isn't much data on whether a second booster will provide that protection. There were no new safety concerns after another dose.
Public fatigue with Covid vaccines could be increased by the idea that another booster is already necessary six months after federal regulators authorized the first round. The government's decision last fall to authorize a first booster saved lives over the winter, according to the evidence. Those who were boosted were 21 times less likely to die from Covid and seven times less likely to be hospitalized than those who were unvaccinated, according to the C.D.C.
Rubin is an infectious diseases expert at the Harvard T.H. Chan School of Public Health. At an event hosted by Columbia University this week, Dr. Kate O'Brien, the director of the vaccines department at the World Health Organization, said, "We are in a relatively weak position on the sort of policy front around exactly."
The Israeli study that has not yet been peer reviewed is the strongest data in support of a second booster. More than half a million adults 60 to 100 years old who had received at least one booster have been studied by the researchers.
There were 232 people who died of Covid if they had only one booster. The 92 people who died of Covid were people who got a second booster. The researchers said that the mortality rate was lower among those who had received an additional booster.
A second booster for the virus could save thousands of lives and prevent tens of thousands of hospitalizations, if it comes back in late spring or summer.
The C.D.C. gave special treatment to Johnson recipients. The agency recommended Moderna's and Pfizer's vaccines for safety reasons.
Adults who got an initial dose plus a booster of Johnson & Johnson's vaccine at least four months ago are eligible for a second booster. The agency cited new data that showed Johnson's vaccine was less effective than the other two.
Pfizer and Moderna both want a second booster. The data collected during the Omicron wave showed that the initial booster's effectiveness waned within three to six months. Researchers haven't tracked the recipients of those boosters for a long time, but data from Israel suggests a second booster restores protection.
The vaccine shield has been weakened by the virus, according to Dr. Paul Burton, Moderna's chief medical officer.
Pfizer and Moderna have an incentive to promote more shots because they are projecting tens of billions of dollars in vaccine sales this year alone.
The new policy was not debated by the F.D.A. or the C.D.C. Dr. Rubin said it was important for the agency to make public any data it relied upon for others to scrutinize. The F.D.A.'s decision memo is expected to be posted soon.
Rubin said that a vaccine that works better than the existing ones is what is needed. The earliest results are not expected until later this spring.
It's not clear what the optimal booster should be, according to Dr. Marks.
The F.D.A. panel will meet on April 6 to discuss the nation's booster strategy. The flu vaccine could be needed in the fall, according to federal health officials.
Next month, the F.D.A. may rule on whether to authorize a vaccine for the nation's youngest children. Moderna plans to submit data from a successful clinical trial of a two-dose regimen for children under the age of 6. Pfizer and BioNTech expect the results of their trial for children under the age of 5 next month.
The F.D.A. would seek input from its advisory committee before making decisions on shots for the youngest children, according to Dr. Marks.
Tuesday's decision authorizes what would be a fifth dose for many Americans with immune deficiencies. Adults can choose between Pfizer's and Moderna's, but those 12 and older can get Pfizer's shot.
It's not clear how much public demand there is for another booster. The nation's enthusiasm for shots has waned with the Pandemic in a lull. The Omicron wave peaked in the third week of January.
According to C.D.C. estimates, the BA.2 subvariant of Omicron is now dominant among new U.S. cases. There have been a lot of new cases in Europe. Some experts think the United States may escape the full impact of the Omicron variant because so many Americans were affected.
Cheryl Shell, a retiree in the town of Spring Arbor in southern Michigan, said she was not waiting around to find out. She got her first booster in November and is eager to get a second.
Kate Bedingfield, the White House communications director, said that the new authorization was a good thing and that the government had plenty of supply to offer second boosters to those now eligible.
She said that Congress will have to provide more money to pay for booster shots if they are recommended for the general population.
Noah and Adeel gave reporting.