Are COVID-19 Booster Shots Variant-Specific?

The rollout of COVID-19 booster shots for some vaccine recipients began in late September—but only for select groups of people at increased risk for COVID-19 exposure or severe illness. All three vaccines—Moderna, Pfizer, and Johnson & Johnson—were authorized for boosters as of November 2021.

Soon after, the FDA authorized a booster dose for all adults who completed their initial COVID-19 vaccine series. The agency then expanded eligibility for the Pfizer booster to children and adolescents ages 5 to 17.

According to the CDC, eligible adults are able to choose any authorized COVID-19 booster. However, it is now recommended that individuals get the Pfizer or Moderna mRNA COVID-19 vaccine over the Johnson & Johnson vaccine, following concerns about blood-clotting side effects. The Johnson & Johnson shot still remains an option for those who are not able or willing to get a different vaccine.

Children and adolescents ages 5 to 17 who completed Pfizer's primary series are only eligible for the Pfizer booster.

The Pfizer and Johnson & Johnson boosters will be administered with the same dosage as the initial vaccine, whereas Moderna’s will be a half dose (50 mcg).

A third dose of the Pfizer-BioNTech and Moderna vaccines has already been authorized by the Food and Drug Administration (FDA) for immunocompromised people who meet certain criteria.

The agency has also authorized additional mRNA booster doses for certain higher-risk individuals.

While vaccine makers are developing and testing next-generation COVID-19 vaccines that will offer better protection against variants of the virus, for now, booster shots won't be different from what people are already familiar with.

Philip Felgner, PhD, the director of the Vaccine Research and Development Center at the University of California, Irvine, tells Verywell that boosters will be “exactly the same" as what vaccinated people got the first time around when it comes to the makeup of the vaccine.

Same Shot, Different Day

In August, the FDA authorized a third vaccine dose for immunocompromised individuals 12 years and older who meet certain criteria. That authorization was later expanded to include children ages five and up.

Shortly after the FDA’s authorization of third doses of the mRNA vaccines for immunocompromised people, President Biden announced a potential booster plan for other vaccinated people to start as soon as September 20.

The White House had originally stated that a person would be able to get a booster dose eight months after becoming fully vaccinated—pending FDA authorization of booster doses.

At this time, the FDA and CDC have authorized a booster shot for all three COVID-19 vaccines available in the U.S.

Whether someone is receiving the third dose as an immunocompromised person or a booster dose that's based on the timing of their last vaccine dose, Felgner says that the shots will be the same formulation as the ones people got before. While Pfizer-BioNTech applied for authorization of its booster shot at the same dosage as the original vaccine, Moderna's booster application was for a 50-microgram dose—half of the initial dosage.

Third Dose vs. Boosters

The Centers for Disease Control and Prevention’s Advisory Committee on Immunization Practices (ACIP) has been clear about the distinction between a third vaccine dose and a booster shot.

In a statement released on September 2, Kristen Nichols, PharmD, BCPS, BCPPS, BCIDP, a senior content management consultant pediatric infectious diseases for Wolters Kluwer, defined booster shots as “doses that are given to people who likely had an adequate initial response but whose immunity may have waned over time.”

Nichols clarified that boosters are for “your typical healthy person who got vaccinated originally but now needs to ‘re-invigorate’ that protection.”

Tackling Variants With Vaccines

While the boosters are more of the same, we may see updated COVID vaccines in the future. “The technology is very agile,” says Felgner. “And they will be able to change it or modify it and then make the next generation version as the virus mutates.”

In a press release, Pfizer-BioNTech announced that it is currently developing a COVID vaccine that “targets the full spike protein of the Delta variant.” The updated version still needs to be thoroughly tested and vetted, and clinical trials are underway.

"If we approach new COVID vaccines that target variants like we do the seasonal flu shot, it wouldn’t necessarily have a specific term,” says Nichols. “New strains are incorporated into the flu vaccine each year based on which strains are expected to be circulating, and we continue to call that just the influenza vaccine.”

Will Boosters Work Against Variants?

Early data on booster doses of the Pfizer-BioNTech and Moderna vaccines have been promising, but there are still some unknowns because of the virus variants that continue to emerge.

Pfizer and BioNTech submitted early-stage clinical trial data to the FDA. In the trials, participants received a booster shot eight to nine months after their second dose.

According to a press release, the results showed that the third dose “elicited significantly higher neutralizing antibodies” against the initial SARS-CoV-2 strain as well as the Beta and Delta variants.

Moderna also initiated the data submission process of early clinical trial data. For the Phase 2 clinical trial, participants received a booster dose six months after getting their second dose. In a press release, Stéphane Bancel, Moderna CEO, said that the booster showed “robust antibody responses against the Delta variant.”

Omicron, a new variant of concern, contains more mutations than previous strains and is thought to spread more easily than the wild-type virus. According to the CDC, the current COVID-19 vaccines are expected to protect against severe illness, hospitalizations, and deaths due to Omicron infection.

Data from preliminary studies conducted by Pfizer show that three doses of the Pfizer vaccine neutralize the Omicron variant, while two doses were significantly less protective.

Similarly, another current study (which has yet to be peer-reviewed) showed that those who received a booster dose of an mRNA vaccine (Moderna or Pfizer) had a strong cross-neutralizing response against Omicron, whereas neutralization was undetectable in most individuals who only completed the primary vaccination series.

As boosters begin to roll out for people who are already vaccinated, it’s important for those who are unvaccinated to initiate their first dose.

“This vaccine is very effective even with the Delta variant that is so aggressive,” says Felgner. "It’s able to prevent the severest form of coronavirus infection.” 

The information in this article is current as of the date listed, which means newer information may be available when you read this. For the most recent updates on COVID-19, visit our coronavirus news page.