COVID-19 Vaccine Booster Doses May Soon Be a Reality. Here’s What Experts Know So Far.

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Photo credit: MarsBars - Getty Images
Photo credit: MarsBars - Getty Images

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Now that the Delta variant of the novel coronavirus is the most common strain responsible for new infections throughout the United States, experts are beginning to push for a booster shot of the COVID-19 vaccines, no matter which option you received.

Pfizer announced this month that it plans to seek FDA authorization for a third dose of its mRNA COVID-19 vaccine in August, citing factors like the rise of the highly transmissible Delta variant and uncertainty about continued efficacy six months or more after the second shot. The founder of Moderna, meanwhile, said in a July 7 interview that he believes a booster shot will “almost certainly” be necessary in the coming months.

And in a February interview with CNBC, Johnson & Johnson CEO Alex Gorsky said that people may need to get the single-dose vaccine each year for several years, similar to the annual flu shot. “Unfortunately, as [the virus] spreads, it can also mutate,” he said. “Every time it mutates, it’s almost like another click of the dial, so to speak, where we can see another variant, another mutation that can have an impact on its ability to fend off antibodies.”

But the Centers for Disease Control and Prevention (CDC) and the U.S. Food and Drug Administration (FDA) disagree; just hours after Pfizer’s July 8 announcement, the agencies released a joint statement saying that “Americans who have been fully vaccinated do not need a booster shot at this time.”

It’s confusing to see COVID-19 vaccine manufacturers and government agencies at odds, especially as cold and flu season approaches. With so much uncertainty about booster shots, we asked doctors to explain why we still don’t know if they’ll be necessary, plus how long we can expect the vaccines to last in the first place.

Back up: How do booster shots for vaccines work?

“For some vaccines, after a while, immunity begins to wear off,” the CDC explains. “At that point, a ‘booster’ dose is needed to bring immunity levels back up.” Booster shots are extra doses of a vaccine administered sometime after an initial dosage has been received, re-upping your body’s immune response.

Some boosters are recommended very infrequently, like one for tetanus, which should be received every decade. Others, like the annual flu vaccine, are more frequent, due to factors like changing pathogens and waning immunity. Different types of flu virus circulate each year, making an annual shot necessary to protect against the most dominant strains each flu season.

SARS-CoV-2, the virus that causes COVID-19, is also mutating, and the variant of most concern is currently Delta, which was first detected in India last December. So far, all of the available COVID-19 vaccines, especially the mRNA ones, appear to offer adequate protection from the Delta variant.

Will you need a COVID-19 vaccine booster shot for full protection?

It’s still unclear, given that the COVID-19 vaccines have only been widely available since December 2020 at the earliest. “At six months, it seems like the vaccines are holding steady,” explains Abhijit Duggal, M.D., a critical care specialist at Cleveland Clinic. But beyond that, no one can say for sure how long immunity will last; the data just does not exist yet.

There are hopeful signs that the protection is better than expected, though. In a June 2021 study published in the journal Nature, researchers found that the mRNA vaccines—those produced by Pfizer and Moderna—trigger an immune response that may offer years-long protection against SARS-CoV-2.

For its part, Johnson & Johnson released a preliminary study with over 40,000 participants (which has not yet been peer-reviewed) on July 1, which shows that antibody response has increased over eight months following the initial dose. In other words, a booster shot might not be necessary yet, since we don’t know how long efficacy will continue to rise.

“It’s still early days in the science,” says William Schaffner, M.D., an infectious disease specialist and professor at the Vanderbilt University School of Medicine. “It may well be that we could use the standard vaccine as a booster to protect against variants—if we need it. We still don’t know how long the standard two-dose vaccine will protect us.”

There are different strategies to deal with variants, adds infectious disease expert Amesh A. Adalja, M.D., senior scholar at the Johns Hopkins Center for Health Security. “One is to reformulate the vaccine, and the other is to add another booster with the same formulation,” he explains. Creating a booster could increase antibodies and T cells (a type of white blood cell that’s an essential part of your immune system) enough to help tackle variants of the original, dominant SARS-CoV-2 strain.

It’s also possible that a booster shot may make an already effective vaccine even more effective. “They may be trying to see if they can get the efficacy up closer to 100%,” says Reynold Panettieri, M.D., director of the Institute for Translational Medicine and Science at Rutgers University.

How effective are the COVID-19 vaccines without boosters?

The mRNA vaccines have been found to be highly effective against the novel coronavirus; one preprint study of nearly 4,000 individuals released in June found that both Pfizer and Moderna offer about 91% efficacy in the real world. But—and this is a big but—this information was gathered before Delta began spreading rapidly. That means there is a possibility that the effectiveness of the vaccines today may be lower than what the data from months ago indicates.

With the new research being conducted, both Pfizer and Moderna are “trying to preemptively address whether the variants could impact the immunity generated by their vaccines,” Dr. Panettieri explains.

An April real-world analysis of the Johnson & Johnson vaccine, meanwhile, found that it was 76.7% effective at preventing COVID-19 infection at least two weeks after vaccination. In other words, all of the available vaccines work incredibly well so far, even without boosters. (For comparison, the annual flu vaccine usually hovers between 40% and 60% efficacy against illness, the CDC explains.)

Bottom line: The jury’s still out on COVID-19 booster doses.

Until medical experts have more data, Dr. Adalja emphasizes that receiving all necessary doses of the COVID-19 vaccines will still offer worthy protection. “The priority still should be getting people vaccinated with the original vaccine, which does have an impact on all of the variants when it comes to what matters—serious illness, hospitalization, and death,” he says.

Until a firm decision is made, the emphasis should be placed on those first and second necessary doses. “The vaccines are so important,” Dr. Duggal explains. “We need to reach a point of as many people being vaccinated as possible, as quickly as possible. That’s the biggest thing we can do to get back to some degree of normalcy.”

Additional reporting by Korin Miller

This article is accurate as of press time. However, as the COVID-19 pandemic rapidly evolves and the scientific community’s understanding of the novel coronavirus develops, some of the information may have changed since it was last updated. While we aim to keep all of our stories up to date, please visit online resources provided by the CDC, WHO, and your local public health department to stay informed on the latest news. Always talk to your doctor for professional medical advice.

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