New Covid boosters look a lot like the old ones. Doctors worry that could lead to errors.

As updated Covid booster shots roll out across the nation, many experts are raising an eyebrow — and perhaps squinting at the label. That's because the new doses come in capped vials that look strikingly similar to the old ones.

It's a design decision, experts say, that could result in some people mistakenly receiving the wrong dose.

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Pfizer-BioNTech’s updated booster for people 12 and up comes in vials that have a gray cap with gray labeling — the same color scheme as its original vaccine, which is still being used for people's primary vaccinations.

Moderna’s updated booster for adults comes in vials that have a dark blue cap with gray labeling; its vaccine vials for children 6 through 11 — which contains the drugmaker's original formulation — have the same dark blue cap. (The vaccine used for primary vaccinations for adults has a red cap.)

"The front-line health care workers are already busy; they have a lot going on," said Dr. Ofer Levy, the director of the Precision Vaccines Program at Boston Children’s Hospital. While both Pfizer and Moderna's labels say what vaccine is inside, making the vaccine vials easy to tell apart prevents "providers from grabbing the wrong one."

Having different colors seems like "the least error-prone solution," he said.

Dr. Celine Gounder, an infectious disease specialist at NYU Langone Health in New York City, agreed.

"Color-coding is one of the most important things that can be done to cue to people which vaccine is which," she said.

The coloring of the vials is essential because it highlights differences between these shots and "enables timely distribution," said Dr. Katherine Poehling, a vaccine expert and pediatrician at Atrium Health Wake Forest Baptist in North Carolina.

This isn’t the first time labeling has sparked confusion. When Pfizer’s original vaccine was first authorized in December 2020, it came in vials labeled as containing enough doses for five immunizations. However, providers soon found that they were able to draw up six and sometimes even seven doses, leaving them unclear on whether they were allowed to administer the extra doses.

Administration errors are also a known issue. After Covid vaccines were authorized for children, there were reports of kids who were accidentally given the adult version, which contains a higher dose. Providers who administer Covid vaccines are required by law to report vaccination errors, including inadvertently administering the wrong dose, to the Centers for Disease Control and Prevention's Vaccine Adverse Event Reporting System, or VAERS.

The color choices were raised as a point of concern during last week's meeting of the CDC's vaccine advisory committee, with some members worried that children might receive the wrong dose.

"I’ve heard of parents who’ve been very concerned about Covid vaccine safety and then have decided to vaccinate and then only to be told that they were vaccinated with a higher dose," Dr. Matthew Daley, a senior investigator at Kaiser Permanente Colorado, said during the meeting. "At some level, we run the risk of losing confidence in the program more broadly the more that that happens."

Moderna said in a statement that it provides educational resources on its website on how to properly administer its vaccine. Pfizer did not respond to a request for comment.

The CDC director, Dr. Rochelle Walensky, said Tuesday during a White House Covid Response Team briefing that the agency is aware of doctors' concerns and is actively working to educate providers and to minimize confusion caused by the caps.

The FDA did not provide a comment by publication time. However, the agency posted on its website letters from Pfizer and Moderna that were sent to health care providers that asked them “to carefully read the labels to differentiate” between the new boosters and the old ones.

Matt Blanchette, a spokesperson for CVS Health, said in statement to NBC News that its pharmacies are "accustomed to adjusting to changes in federal vaccination guidelines" and has systematic safety checks in place to ensure proper administration.

Walgreens did not respond to a request for comment.

But even with measures in place, vaccination errors with the new boosters will likely happen, said Dr. William Schaffner, an infectious diseases expert at the Vanderbilt University Medical Center.

"When you’re giving millions of doses of vaccine, as we do every day in the United States and have for years, there will be administration errors," he said, adding that these mistakes are more likely to happen in understaffed clinics.

"If you have sufficient personnel, have someone else double-check to make sure you’ve got the right vial in hand," he said.

Gounder, of NYU Langone Health, advised storing the different doses in different places to avoid errors.

"I think having them stored in separate places — depending on the dosage and the formulation — I think is the best you're going to be able to do," she said.

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This article was originally published on NBCNews.com