Scientists say COVID-19 booster shots aren't needed yet—here's why

The past week has been a wild ride for fully vaccinated Americans seeking clarity on whether they will need COVID-19 booster shots—either now or in the future, particularly as more contagious variants emerge.

On July 8, Pfizer and BioNTech announced they planned to seek emergency authorization for a booster dose of their vaccine, saying that their data shows their vaccine’s efficacy is waning and that a booster “may be needed within six to 12 months after full vaccination.” Pfizer representatives later met with U.S. officials to press their case for emergency authorization of a third dose.

U.S. regulators, however, have pushed back on Pfizer’s claims. In a joint statement, the U.S. Food and Drug Administration and the Centers for Disease Control and Prevention said that Americans who have been fully vaccinated “do not need a booster shot at this time,” emphasizing that the vaccines remain highly effective against severe disease and death.

A spokesperson from the Department of Health and Human Services tells National Geographic that regulators are taking all data into consideration—including those from research labs, clinical trials, and pharmaceutical companies like Pfizer. “We appreciate the information they shared, and officials continue to engage in a science-based rigorous process to consider whether, when, or for whom a booster might be necessary.”

In fact, contrary to Pfizer’s study, new laboratory data has emerged suggesting that the Pfizer vaccine offers protection that could last for years. So what exactly is going on? Here’s a look at what the data shows about how long immunity lasts among the fully vaccinated—and what scientists want to know before they recommend giving anyone another dose.

Antibodies aren’t everything

First, a quick primer on the body’s immune response. It typically has two phases: Innate immunity is the first line of defense, immediately generating a general immune response that can destroy foreign substances or germs. Then the adaptive immune system—which targets specific bacteria and viruses—kicks in to make antibodies to shield against that pathogen in the short and long term.

It does so with the help of T cells and B cells, two types of white blood cells. As E. John Wherry, director of the Institute for Immunology at the University of Pennsylvania, puts it, T cells “are kind of the orchestrators of these complex immune responses.” They nurture the B cells, which mature and transform into plasma cells with one mission: “They are antibody factories,” Wherry says.

But studies have shown that the levels of neutralizing antibodies generated by the COVID vaccines do decline over time. In its statement last week, Pfizer said that a third dose of its vaccine elicits an antibody response five to 10 times higher than after two doses. Pfizer has not released its data, however; a spokesperson told National Geographic that the company is preparing it for publication.

Wherry says that there’s no doubt that the presence of neutralizing antibodies is critically important—but that they’re not everything.

Jane O’Halloran, assistant professor of medicine at Washington University School of Medicine in St. Louis, Missouri, agrees, pointing out that scientists expect to see a decline in antibody levels. “If you had high levels of antibodies to every pathogen that you come across, your blood would be sludge,” she says.

So it’s not about the quantity of the antibodies. It’s about their quality—making sure that the antibodies present are actually doing the job and that your body has the tools to quickly create them when they’re needed.

Training camps of the immune system

O’Halloran was part of a research team that set out to investigate whether the vaccines are indeed preparing the body to fight COVID-19 over the long haul. In their study, they took samples from lymph nodes—which contain B and T cells—of 14 healthy adults who received the Pfizer vaccine.

When the B and T white blood cells respond to a disease and interact with one another, they create something known as germinal centers—essentially training camps for the immune system. Found in the lymph nodes, the germinal centers are where plasma cells learn how to make antibodies that will be most effective in fighting a pathogen.

The germinal centers also produce memory cells that can stick around for a longer time and help the body mount an immune response if it encounters the virus or bacterium again later in life. Unlike antibodies, memory cells can’t “see” a virus until it infects cells in part of the body. When that happens, however, they jump into action and eliminate the infection.

In late June, O’Halloran and her team at the Washington University School of Medicine researchers published their study in the journal Nature showing that germinal centers were still forming in participants for up to 15 weeks after vaccination. Although that might not seem like a long time, O’Halloran says the idea is that those germinal centers “are potentially producing these long-lived memory cells that we need to give long-term immunity.” The study’s lead author Ali Ellebedy told National Institutes of Health director Francis Collins that the germinal center response is so robust that he believes it could last for years.

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“This gives us insight that the body is doing what it’s supposed to be doing,” O’Halloran says. Wherry, who wasn’t involved with the study, agrees. “Now we know for sure that’s happening really robustly with these vaccines,” he says.

But the study provides a fairly small dataset, particularly when compared to the abundant studies measuring antibody levels. That’s because studies like this one are much harder and take longer—meaning fewer researchers have been able to take them on.

“Sometimes the easy bit to measure is not the thing that gives us the best window into what’s going on in the body,” O’Halloran says.

O’Halloran also points out the study only speaks to the durability of the Pfizer shot. Some observers have extrapolated that Moderna’s vaccine may have similar durability since it relies on the same mRNA technology. But for that and the Johnson & Johnson vaccine, O’Halloran says, you’ll have to look to how they’re performing in the real world.

Reassuring real-world data

Another argument Pfizer has made for booster shots has pointed to real-world data out of Israel showing that the efficacy of its vaccine declines six months after full vaccination. On July 5, Israel’s Ministry of Health said that it has observed a “marked decline” in the vaccine’s efficacy to 64 percent in preventing both infection and symptomatic illness.

There’s also some indication that protections are waning among the immunocompromised, leading Israel to begin administering a third jab to transplant patients. (Here’s why COVID-19 vaccines are so complex for immunocompromised people.)

Wherry says that the dramatic decline in efficacy in Israel can be attributed in part to the country’s robust COVID-19 testing program. “They test everybody all the time,” he says. “They’re picking up asymptomatic infections.”

He points out that Israel’s data shows the vaccine remains 93 percent effective in preventing serious illness and hospitalization. This suggests that, while the vaccines may no longer be producing the robust levels of antibodies that shield people entirely from infection, the long-term memory response is still kicking in and preventing the infection from spreading.

Public health data elsewhere would seem to back that up: Earlier this month, CDC director Rochelle Walensky said that more than 99 percent of the U.S. deaths from COVID-19 in June were among unvaccinated people. O’Halloran says that’s really the point of getting vaccinated.

“At no point have the vaccines been said to 100 percent prevent infection,” O’Halloran says. “The most important thing is their impact on severe disease and death.”

Critically, the Pfizer, Moderna, and Johnson & Johnson vaccines have all been shown to be effective against Delta and other variants of concern. Of course, that could change or new variants could arise that evade the vaccines’ protections. But O’Halloran points out that booster shots aren’t really the best way to deal with the threat of variants.

“The best way to do that is to get everybody vaccinated once rather than finessing the potential incremental benefit you might from a booster vaccine in one group when you have a whole other group of people who aren’t vaccinated at all,” O’Halloran says.

What the data doesn’t show

While the existing data does offer reassurance that the vaccines remain protective—and booster shots aren’t needed—scientists and regulators alike point to the need for more academic studies to untangle exactly how the immune system is responding to the COVID-19 vaccines.

“I think what we’re going to see, over the next six months or so, a lot of studies outlining what those other components of the immune response look like in both healthy people and in some of our vulnerable populations,” Wherry says. “We really just need a lot more information on multiple layers of the immune response to vaccination.”

It’s also important to keep an eye on public-health data, particularly the rate of hospitalizations and deaths among vaccinated people. Wherry says that, ideally, states will be able to pinpoint when those who are infected were first vaccinated to help identify when immunity seems to be waning.

The HHS spokesperson says regulators are monitoring all this new data as well. “The administration is prepared for booster doses if and when the science demonstrates that they are needed, and any recommendation by CDC and FDA would come after their thorough review process.”

All the same, Wherry says it can’t hurt to be prepared for the time when boosters are needed. “Right now you can have confidence that, if you’re fully vaccinated, your chances of getting severely ill from COVID are extremely low in the U.S.”