(WASHINGTON) — With little fanfare, the U.S. Food and Drug Administration gave Pfizer permission this week to store its COVID-19 vaccine in a typical refrigerator for one month — freeing the vaccine from the need to be shipped in cumbersome boxes stuffed with dry ice.

Among authorized COVID-19 vaccines, Pfizer’s vaccine was notorious for its ultra-cold storage requirements. Now, as the only vaccine authorized for children ages 12 to 17, this new flexibility could dramatically accelerate the effort to vaccinate America’s teens and adolescents.

“The ability to store Pfizer vaccine in refrigerators for a period of time is great news as this makes the vaccine more readily available to the public because community clinicians like me are able to get, store and deliver vaccinations to help us reach the last mile, have more flexibility in distribution plans and reach areas where vaccines may be harder to access in a timely manner,” said Dr. Jay Bhatt, an internist in Chicago and an ABC News medical contributor.

Since the early days of the vaccine race, scientists at both Pfizer and Moderna have fixated on storage temperature. Both vaccines rely on a molecule called messenger RNA, or mRNA, which is extremely fragile. This meant distribution sites would have to be limited and the cost and difficulty of shipments would be high.

When the vaccines were authorized last December, both required ultra-cold temperatures for long-term storage. But Moderna proved to the FDA that its vaccine was stable for a month in cooler temperatures — such as a standard refrigerator. Pfizer’s vaccine, meanwhile, could only be kept in a fridge for five days, meaning this vaccine was often earmarked for use in cities, where medical centers had access to deep-freeze storage.

Now, Pfizer’s new convenient storage requirements break down one more barrier in reaching wider portions of the population.

Experts said the Pfizer vaccine will now have better local access, with greater flexibility for walk-in appointments and primary care access to vaccine supply. Meanwhile, there will be less concern about the vaccines going to waste. And for adolescents and teens — who now comprise more than a quarter of reported daily vaccinations — the simplification in storage requirements brings further opportunities to vaccinate in pediatrician offices and school settings.

Alongside the change in cold storage, Pfizer is also preparing to distribute smaller packages of doses — a box of 450 — in addition to the prior size of 1,170. This flexibility means that smaller clinical settings that support harder to reach populations may be in a better position to receive shipments.

“Allowing both Pfizer and Moderna’s COVID-19 vaccines to be stored at refrigerator temperatures and to be distributed in smaller quantities will make a tremendous impact on both access and equity of vaccine distribution. These changes mean that the vaccine can be delivered more easily in people’s neighborhoods, on mobile vans, and importantly at community health centers,” Dr. Katherine Gergen Barnett, vice chair of primary care innovation and transformation and the program director in the department of family medicine at Boston Medical Center, told ABC News.

The science of ultra-cold

It took decades of scientific research to invent mRNA vaccines and figure out how to store them at a reasonable temperature. The journey was beset by challenges.

First, it was difficult to get mRNA into a cell; the body quickly degraded it. Scientists overcame those hurdles by using synthetic RNA that the body’s immune system doesn’t recognize and encasing that material in lipid nanoparticles. These strands of genetic code in the COVID-19 vaccine carry instructions that the human cell uses to manufacture the spike protein, which sits on the surface of SARS-CoV-2.

If the RNA strand bends, it can spark a reaction that cuts the message off and there is a loss of function. To slow degradation, scientists keep the vaccines at low temperatures. The lower the temperatures, the slower the molecular movements and the lower the chance of damaging reactions. For an mRNA vaccine to work, the structure of the mRNA, as well as the fat bubbles encasing it, must be injected intact.

Now, as science continues to evolve, new versions of even more stable mRNA vaccines for COVID-19 seem to be on the horizon. And experts are hopeful mRNA could be used to develop vaccines for HIV, influenza, Zika and rabies, all of which will benefit from the discoveries of today.

“This important move to bring vaccines more locally removes some barriers to access — people can receive the vaccine in their homes, do not have to take extra time from work, can receive the vaccine from people they trust — and ultimately is a tool in creating greater health equity,” Gergen Barnett said.

Rebecca Weintraub, M.D., is an assistant professor at Harvard Medical School and associate physician at Brigham and Women’s Hospital.

John Brownstein, Ph.D., is an ABC News contributor. He’s also the chief innovation officer at Boston Children’s Hospital and a professor at Harvard Medical School.

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