Why Do Health Officials Suggest Getting a COVID-19 Booster Shot After 8 Months?

In August 2021, health officials recommended that most Americans should get an additional dose of mRNA COVID-19 vaccine. During that time, medical experts said the booster shots should be administered starting eight months after the second dose.

In a meeting with Israeli Prime Minister Naftali Bennett, President Joe Biden said U.S. health officials had considered giving booster shots as soon as five months, following Israel’s lead.

Anthony Fauci, chief medical advisor to Biden, in August reiterated the original plan of administering boosters at eight months. He did acknowledge, however, that the timeline was “flexible,” depending on new data about the longevity of vaccine efficacy.

A Centers for Disease Control and Prevention (CDC) advisory panel presented five studies that indicated a drop in vaccine efficacies against infection around the five-month mark, with major declines seen when Delta became dominant in the United States.

However, there were no major increases in severe illness, hospitalization or death among fully vaccinated people, even months after finishing the original regimen.

The Food and Drug Administration (FDA) has since authorized a booster dose for all individuals 5 years and older who meet eligibility criteria.

How Boosters Support the Immune System

Since the early days of the COVID-19 vaccine rollout, experts have suggested boosters would be necessary to support vaccinated people’s immune systems.

“We know that even highly effective vaccines become less effective over time,” U.S. Surgeon General Vivek Murthy said at a media briefing for the booster plan.

Initial vaccinations kick-start the immune system, spurring the creation of neutralizing antibodies and T-cells, which attack pathogens and infected cells. The body can then learn to recognize the virus and work to neutralize it after the immune response has waned.

Over time, the body loses some of the antibodies, and instead relies on “immune memory” by the B- and T-cells.

Scientists don’t know the exact antibody levels necessary to mount a sufficient immune response. If they knew this threshold, health officials may be able to better judge when to administer a booster shot, Kate Mullane, DO, PharmD, professor of medicine and infectious disease specialist at the University of Chicago, tells Verywell.

Instead, health officials looked to data on breakthrough infections to create the timeline.

“We rely on all of the wonderful volunteers for our studies, and on countries who early on vaccinated everybody, like Israel. We follow those people and if we see that the vaccine is losing efficacy or people are getting sick, then as that number rises, we know the efficacy of our vaccine is falling,” Mullane says.

Data from Pfizer shows that the amount of neutralizing antibodies one month after the third dose was three times higher than the level after the second shot. 

A recent study tested antibodies created by the Moderna vaccines against six major variants (Alpha, Beta, Gamma, Epsilon, Iota, and Delta) and found that they persisted, though at low levels. Mehul Suthar, PhD, an assistant professor at the Emory Vaccine Center and an author of the study, says that a third mRNA shot will generate a more robust immune response.

“Providing a boost may put you where you were two weeks after the second dose, where you have peak immunogenicity and peak vaccine efficacy data,” Suthar tells Verywell.

How Did Officials Come Up With the 8-Month Timeline?

When deciding the timeline for booster recommendations, health officials turned to various studies.

Data from Israel indicates that vaccine effectiveness against infection in people older than 60 fell significantly over the course of five months. The country is now administering boosters to people as young as 12 years old, at least five months after their original vaccination.

The timeline in the U.S. is subject to change, as demonstrated by the FDA's recent approval.

Suthar says that it’s difficult to know how much the spread of the Delta variant has altered the effectiveness of the vaccines, and how that shifts the timeline for booster shots.

“I think eight months is a reasonable timeframe. My anticipation was probably going to be around nine months to a year, so I’m a little surprised to see eight months,” Suthar says.

“But at the same time, I think this delta variant is just so robust. It’s a variant that we haven’t seen this dominant and this contagious before,” he continues. “That does sort of alter potential plans about when booster should be taken after the second dose or first dose.”

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