The Food and Drug Administration has authorized a second Covid-19 booster shot for people ages 50 and older, but several public health experts said younger, healthier members of that group don't necessarily need a fourth shot as soon as they become eligible.
"This is one of those where I don’t think anyone needs to race," Dr. Richard Besser, former acting director of the Centers for Disease Control and Prevention, told NBC’s "TODAY" show on Wednesday. "This is one of those things where people should think thoughtfully."
The FDA's authorization, announced Tuesday and promptly followed by new CDC guidance, allows anyone 50 and older to seek a fourth dose of the Pfizer-BioNTech or the Moderna vaccine at least four months after their initial booster. Immunocompromised people, for whom a three-shot regimen is considered the primary vaccination series, can seek a second booster as well.
The CDC also recommended that adults who've gotten two Johnson & Johnson doses get an additional Pfizer or Moderna booster.
But Dr. Prathit Kulkarni, an infectious disease expert and assistant professor at Baylor College of Medicine, described a sliding scale of vaccination need.
While older adults and those with underlying health conditions should seriously consider the newly available booster soon, others could determine the timing based on their own risks and circumstances, he said.
"There is a difference between somebody who is 51 and otherwise healthy without any major medical problems and somebody who is 85 and has multiple medical problems," Kulkarni said. "Their risk profile from potentially having a bad outcome from Covid-19 is fairly different."
"The bottom line is, it depends on individual risk profile: What is your age? What are your comorbidities?" he added.
Dr. Peter Chin-Hong, a professor of infectious diseases at the University of California, San Francisco, said he plans to seek a second booster for his mother, who is in her mid-80s.
"But for healthy 50-year-olds, that probably isn't as important if they've gotten three shots because three shots is really the sweet spot," Chin-Hong said. "You give a one-two punch and then you wait a little bit, and then you give a booster to remind the system."
Still, Chin-Hong added, if a healthy 50-year-old is eager for a fourth shot, any potential risks of getting another dose are extremely low.
"There's a theoretical negative. We've talked theoretically about immune exhaustion phenomenon, where the immune system just sees too much vaccine over and over and it just stops reacting," Chin-Hong said. "But again, that's just theoretical."
In Israel, people over 60 have been eligible for a fourth shot since January. Recent data from the country suggested that death rates were lower among people who opted for the extra dose than for those who received just one booster.
Besser said some people could consider timing their additional booster around local transmission trends. Those in low-risk areas might be able to hold off for now, then get the fourth shot once they see a spike in infections beginning.
"What I would see as a potential downside is if you’re in an area where it’s really, really low and you get the booster now, and two, three months from now, the rate goes up higher," Besser told "TODAY."
"I don’t know you’re going to have the same protection then if you wait a couple months, so that’s why I would say pay attention to what’s going on locally," he said.
Chin-Hong agreed that there may be value in holding off, noting a comparison of the strategy to stock market investing.
"Three shots — that first boost — is the most important, so you can definitely roll the dice and wait," he said. "Someone has likened it to the stock market: You don't know what's coming, but you can see when the stock is going up before the stock goes really up, to make the most money."
Nearly 70 percent of Americans over age 5 have gotten either two Pfizer or Moderna shots or one J&j dose, according to the CDC. Nearly 45 percent of that vaccinated population has been boosted.
The U.S. has recorded more than 983,000 Covid deaths since the pandemic began more than two years ago, according to NBC News' tally.