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Here's Why You'll Probably Need a COVID-19 Booster Shot

A pattern of COVID-19 vaccine ampules on a light green background.

Iuliia Shisterova / Getty Images

Key Takeaways

  • Vaccine makers like Moderna are developing and testing booster shots to help immunize against the variants of the SARS-CoV-2 virus that are circulating in the U.S.
  • Booster shots are also needed to increase immunity as protection from the original shot wanes.
  • The Moderna, Pfizer-BioNTech, and Johnson & Johnson vaccines do provide protection against the virus strains circulating in the U.S. are highly effective at reducing hospitalizations and deaths.

More than half of U.S. adults have now received at least one dose of the three available COVID-19 vaccines. But with the rise of virus variants and the potential for waning vaccine-induced immunity, experts are saying even the fully vaccinated may soon need booster shots.

Variants Driving Need for Boosters

Several variants of SARS-CoV-2, the virus that causes COVID-19, are circulating in the U.S. Some, notably B.1.351, have mutations that appear to reduce the effectiveness of the COVID-19 vaccines that are currently available.

Vaccine makers are already planning ahead in an effort to address the immunological challenge posed by variants. At the end of March, Moderna shipped supplies of a booster vaccine against the B.1.351 variant to the National Institutes of Health (NIH) for phase 1 clinical trials and reports that its own phase 2 clinical trials on the boosters are already underway.

In a statement released on April 20, Moderna's chief executive officer Stéphane Bancel said that "recent preclinical results have shown that our variant-specific booster candidates were effective against COVID-19 variants of concern, and we hope to continue to see positive results from the clinical studies."

Moderna's variant-specific vaccine candidates include one specifically targeted against the B.1.351 variant and a multivalent booster (for any variant) that combines the company's original vaccine and their shot offering protection against B.1.351 in a single dose.

Moderna notes that its current vaccine provides neutralizing activity against current variants of the virus, but that booster doses are intended to increase that immunity. 

How Much of a Threat Are Variants?

The Centers for Disease Control and Prevention (CDC) created 3 classifications for SARS-CoV-2 variants: a variant of interest, a variant of concern, and a variant of high consequence. Currently, the CDC has not identified any variants of high consequence in the U.S.

The B.1.351, first identified in South Africa, spread to several states, according to the CDC. It is more easily transmissible than the original forms of the virus.

During a press conference held by Johns Hopkins, Anna Durbin, MD, professor in the department of international health at Johns Hopkins Bloomberg School of Public Health, explained that "most of the [vaccine] companies are in fact developing and testing booster shots of their vaccines and importantly I think, to note, is that this booster will likely cover the most extreme variant that we know of, the South African variant."

Variants of Concern

There are five variants of concern currently circulating in the U.S.:

  • B.1.1.7. This variant was first detected in Britain. It was identified in the U.S. in December 2020. It is more easily transmissible and appears to cause more severe disease than the original virus.
  • B.1.351. This variant was first identified in South Africa in December 2020 and has been known to be in the U.S. since the end of January 2021. It is more easily transmissible than the original virus, and the current vaccines may be less effective against it. 
  • P.1. This variant was initially identified in Brazil and Japan in early January. It was first detected in the U.S. in January 2021.
  • B.1.427 and B.1.429. These two variants were first identified in California in February 2021. These are slightly more transmissible than the original virus.

Waning Immunity

Because immunity created by most vaccines wanes with time, booster shots will likely be a necessity. It is not unusual for vaccines to require boosters in order to maintain high levels of immunity.

In an interview with CNBC, BioNTech's co-founder and chief medical office, Ozlem Tureci, MD, said that she expects people will need to be vaccinated against SARS-CoV-2 annually because of the decrease in immunity.

During the Johns Hopkins press conference, Naor Bar-Zeev, PhD, MPH, associate professor in the department of international health and the deputy director of the International Vaccine Access Center at Johns Hopkins Bloomberg School of Public Health, pointed out that “we have to have a tetanus shot every ten years and older adults need a pneumococcal vaccine every five years."

Bar-Zeev said that boosters become "all the more [important] in the current context of variants emerging. We will have the opportunity to reboost, to revaccinate, and to broaden our protection, and not only make it more long-lasting.”

During the same press conference, Durbin noted that combinations of the different existing vaccines are already being tested. In the U.K., researchers are combining mRNA vaccines (like the Moderna and Pfizer-BioNTech) with a dose of an adenovirus-based vaccine (like the Johnson & Johnson vaccine) later on as a sort of booster shot—or vice versa.

“The best way to reduce the emergence of variants and their dominance across the world is to reduce transmission of the virus in populations everywhere,” Bar-Zeev said. “And that can be achieved through high coverage with the existing vaccines. It can be achieved through maximizing the breadth of vaccine products that are available, maximizing their production, and maximizing their delivery around the world.”

Durbin added that vaccines are also important strategies for reducing the risk of severe illness and hospitalization from COVID-19, as well as deaths. "These are the critical efficacy endpoints that will make a public health impact and get us out of this pandemic,” Durbin said. “The vaccines are providing us light at the end of the tunnel, but we need to ensure global vaccine access because we will not be entirely out of the pandemic until the world is vaccinated.”

Vaccines Alone Are Not Enough

Bar-Zeev cautioned against viewing vaccines alone as being enough to turn the COVID-19 pandemic around. “Vaccines are enormously powerful tools in public health, but they're not the only tool."

As vaccination efforts continue, Bar-Zeev stated that "we need to maximize every tool we have at our disposal, and that does include masks and it includes distancing, and it includes public restrictions where appropriate."

What This Means For You

The variants of COVID-19 that are circulating around the world, as well as the waning of vaccine-induced immunity with time, motivated vaccine manufacturers to work on booster shots. It's likely that at some point, even if you've been fully vaccinated, you'll need to get a third dose to ensure lasting protection.

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.

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  1. Wang P, Liu L, Iketani S, et al. Increased resistance of SARS-CoV-2 variants B.1.351 and B.1.1.7 to antibody neutralization. Preprint. medRxiv. doi:10.1101/2021.01.25.428137

  2. Moderna. Moderna announces new supply agreement with Israel for 2022. Updated April 20, 2021.

  3. Centers for Disease Control and Prevention (CDC). U.S. COVID-19 cases caused by variants. Updated April 21, 2021.