Though a third dose of an mRNA vaccine has been shown to provide a boost of protection against COVID-19—even from the Omicron variant—new research shows that protection wanes by the fourth month after vaccination.
The study, released by the Centers for Disease Control and Prevention (CDC) last week, brings up questions about if (and when) all may need a fourth dose of a COVID-19 vaccine in order to remain protected as the pandemic wears on.
When asked about the need of a potential fourth dose, Anthony Fauci, MD, the chief medical adviser to the White House, commented that there may be a need for some—but the data isn’t there yet. “There may be a need for yet again another boost—in this case, a fourth-dose boost for an individual receiving the mRNA—that could be based on age, as well as underlying conditions,” Dr Fauci told reporters at a White House press briefing.
Some people are also already receiving the fourth dose: the CDC recommends people who received an mRNA vaccine and are immunocompromised receive a booster dose—essentially a fourth shot—for COVID-19 protection. So will this new information lead to all receiving a fourth jab? Here’s what infectious disease experts think.
How effective are boosters, and how long do they last?
The CDC currently recommends most Americans ages 12 and older who received an mRNA primary series receive a third dose (booster) of the COVID vaccine to stay up to date. This booster dose should come five months after the second dose of a primary series.
That third dose is beneficial—the new CDC study shows that during both the Delta and Omicron waves, vaccine effectiveness was greater after three doses of an mRNA vaccine versus two doses. That data aligns with previous findings from the CDC, published in January, that a third mRNA dose was highly effective at preventing emergency department and urgent care visits (94 percent during the Delta wave; 82 percent during the Omicron wave) and hospitalisations (94 percent during Delta, 90 percent during Omicron).
But what this new research set out to determine was how long the effectiveness of a third booster would last. To do this, researchers analysed 241,204 emergency department/urgent care encounters, and 93,408 hospitalisations across 10 states from August 26, 2021–January 22, 2022.
In people who received a third dose—either as a third primary dose or a booster dose—the vaccine was 87 percent effective against the emergency department or urgent care visits in the two months after the shot. That number dropped to 66 percent effective after four to five months. The same trend was seen in hospitalisations: A third dose was shown to be 91 percent effective against hospitalisations from COVID-19 up to two months after the shot; the effectiveness dropped to 78 percent after four months or more.
The new research—combined with past reports—emphasises the importance of remaining up to date on your COVID-19 vaccinations. Though protection does seem to wane after a certain amount of time, it’s still highly protective against serious illness. “COVID-19 vaccines [and] booster shots can keep you out of the hospital and certainly can save your life,” Dr Fauci said during the press briefing. “If you haven’t gotten a booster shot at all, then you should definitely get one,” David Dowdy, MD, an associate professor of epidemiology at the Johns Hopkins Bloomberg School of Public Health, tells Health. However, if you caught COVID-19 during the most recent, Omicron-dominant phase of the pandemic, you should wait three months after a full recovery to get a booster, he says.
Who is currently able to get a fourth shot?
Because some people who are immunocompromised received three full doses of an mRNA vaccine, in accordance with CDC guidelines, those individuals may now receive a fourth dose in the form of a booster. But they’re the only ones approved for a fourth dose.
“This whole notion of a fourth dose is right now really only being implemented in people who are immunocompromised in some way, and, in the US, only for people who are moderate to severely immunocompromised,” Dr Poland says.
Immunocompromised people include those who have received an organ transplant and are taking immunosuppressant drugs, individuals with untreated or advanced HIV, those being treated for blood cancers and tumours, among others, according to the CDC.
People ages 12 and up who are immunocompromised and received a Pfizer-BioNtech vaccine can receive a fourth or booster dose three months after their third primary dose. Moderna booster doses are reserved for people ages 18 or older—again, three months after a third primary, the CDC says.
Will all adults need a fourth shot at some point?
We don’t have data suggesting that all adults need a fourth dose right now, according to experts. “If you’ve gotten a booster shot already and you have an intact immune system, there’s no need for a fourth dose at this time,” Dr Dowdy says.
Whether fourth doses—or more—will become standard operating procedure in the US will depend on the timing and severity of future waves of the virus. “I do think that we will see a recommendation for a fourth dose whenever we see another wave of COVID-19. And that shot will be timed more to the timing of the wave of disease, not to how long it’s been since your last vaccine dose,” Dr Dowdy says. The next time one could be asked to get another shot might be the fall, the New York Times recently reported.
While Dr Poland suggests that “periodic” COVID-19 boosters for most in the future are not out of the realm of possibility, he says that the frequency of additional doses must be balanced with a sense of a person’s real risk of developing severe disease. “Would you get the fourth dose for a 3 percent benefit? Ten? 20? 40? 70? What’s that level? We just don’t know,” he says.
And if you’re expecting a government-manded fourth dose, that may not come either. “I doubt that ongoing COVID boosters will be a requirement from the government,” says Dr Dowdy. “If we do have regular COVID boosters, it will probably be something akin to flu shots now: They are offered before waves come, do provide protection, and may be required of certain groups, like healthcare workers, who pose a risk of transmission to immunocompromised people.”
But for now, a third dose of an mRNA vaccine seems to be enough for many people—even with some waning protection. “For people who have been vaccinated, COVID-19 is already no worse than the flu in severity,” says Dr Dowdy. “So it’s hard for me to see that we would have a policy that is more stringent for COVID-19 than for the flu.”
The information in this story is accurate as of press time. However, as the situation surrounding COVID-19 continues to evolve, it’s possible that some data have changed since publication. While Health is trying to keep our stories as up-to-date as possible, we also encourage readers to stay informed on news and recommendations for their own communities by using the CDC, WHO, and their local public health department as resources.
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