As the number of coronavirus cases in the United States continues to fall, people’s immunity may also decline. Several studies have shown that while mRNA booster injections have been successful in preventing hospitalization and death, their effectiveness against infections is declining.
It’s no wonder, then, that at the end of Thursday, Moderna sought emergency use approval from the Food and Drug Administration for a second booster shot for all adults. The company’s request came just days after Pfizer and BioNTech filed for emergency approval for a second booster of its coronavirus vaccine for people 65 and older.
Moderna said the much broader request would give the Centers for Disease Control and Prevention, as well as health care providers, more flexibility in determining who would benefit most from getting an additional booster shot and when.
Scientists and doctors are very divided on this. “I don’t think everyone should get a booster right now,” said Dr. Yvonne Maldonado, a pediatric infectious disease physician at Stanford University. “But I see no reason why we shouldn’t start reviewing the available data.”
Who is currently eligible for a fourth vaccine dose?
As of now, the only people allowed to receive a fourth dose are those with weakened immune systems. This includes teens and adults who have had an organ or stem cell transplant, are undergoing chemotherapy for cancer, have advanced or untreated HIV, or are taking immune-suppressing drugs.
It’s hard to predict how soon — or if — the FDA could approve a second booster (or fourth dose) for all adults. The agency is expected to convene an advisory committee next month to discuss the matter. And while experts say it’s reasonable that the committee could respond quickly to Pfizer’s older adult request, it’s unclear whether Moderna’s more sweeping request will get the green light.
“We know that people over 65, even if they are vaccinated, have a higher risk of dying than those under 65,” said Dr. Carlos del Rio, an infectious disease specialist at Emory University. “That’s significantly lowered when people get a boost.”
One of the reasons older adults may benefit from an extra booster shot is that as the immune system ages, it tends to weaken and not produce the same amount or quality of antibodies as when it was younger. In addition, older adults often have other medical conditions that demand the attention of the body, putting them at greater risk for serious illness, said Dr. Christian Gaebler, an immunology researcher at Rockefeller University in New York City. “Diabetes, hypertension, obesity and chronic kidney disease are all risk factors for severe Covid,” he said. “And we know that these usually manifest in old age.”
In their justification for seeking second boosters for people 65 and older, Pfizer and BioNTech relied heavily on evidence from two studies conducted in Israel that suggested that people who received a fourth injection were less likely to become infected. with the virus compared to those who had received three doses.
In one study, published on a preprint server in February, scientists reviewed the health records of about 1.1 million people over 60 who had received a fourth dose and compared it with those who had received only three doses. They found that the number of confirmed infections, as well as that of serious illness, was lower in people who had received their fourth injection.
The second study, published Wednesday in The New England Journal of Medicine, looked at Israeli health professionals of all ages and found that both the fourth injection of Pfizer and Moderna increased antibody levels, although they weren’t very good at preventing infection.
However, experts cautioned that the available data is still preliminary and has not yet shown how long the benefits of a fourth dose will last.
If the shooting is allowed for seniors, how should they think about the timing of it?
Experts monitoring Covid-19 are careful not to provide specific advice on when to get a fourth dose if safety and efficacy data are still limited.
For example, if a new wave is on the way, seniors may benefit from getting an additional shot once authorized. But if the next wave doesn’t come until the summer or even the fall, getting a booster now could backfire as the recipients’ immunity could wane by the time they need protection most. Current vaccines are based on the original strain of the coronavirus, so getting a booster now may also do little to protect against future variants.
“It would be great if we knew exactly when the next wave would be so we could vaccinate people ahead of time,” said Dr. Amy Sherman, an infectious disease physician at Brigham and Women’s Hospital in Boston. “But I think we’re not quite there yet where we have a clear seasonality, and we know the exact pace and dynamics of Covid and newer variants.”
That said, if a fourth shot is allowed for adults over 65, and it’s been several months since they got their first booster, “I’d start thinking about whether I need a booster now,” said Dr. delRio.
What does this mean for everyone else?
For people under age 65, who are otherwise healthy, most experts agree that three doses are probably enough for now. For example, those in their 20s and 30s who have already received three injections of the vaccine will see only marginal benefits in protection from an additional shot, said Dr. gaebler.
“Fourth doses may prove advisable,” he said, “but at this point I think the focus should be on administering third doses.”
dr. del Rio agreed. “I’m more concerned about the millions of Americans who are not or only partially vaccinated,” he said. “That to me is where we should put our main focus.” Vaccinating more people, both nationally and globally, could potentially have a greater effect on reducing virus transmission and curbing new variants so everyone can return to normal life, said Dr. delRio.
And there is hope that better vaccines and treatments are on the way. Pfizer and Moderna are testing new Omicron-specific versions of the Covid booster. And other researchers are investigating vaccines that boost mucosal immunity in the nose, as well as protein-based injections that may provide better protection against the coronavirus in the future.
“We really need to think carefully about our vaccine strategies,” said Dr. Sherman. “As a society, we need to think about what our goal is with repeated boosters and vaccines, because none of our existing vaccines completely prevent transmission or all diseases. And so at what point are we comfortable with an asymptomatic or mild infection in the population, while still being able to protect those who are vulnerable?”