mRNA vaccines must be stored at extremely cold temperatures.
The mRNA technology used to create the first two COVID-19 vaccines from Pfizer Inc., and Moderna, Inc. will undoubtedly change the course of vaccine development for years to come.
Both companies have “shown that the vaccines are extraordinary,” says Peter Palese, PhD, the Horace W. Goldsmith Professor and Chair of the Department of Microbiology, at the Icahn School of Medicine at Mount Sinai. The Pfizer vaccine began being administered to high-risk U.S. health care workers on Monday, December 14. This marks the first time mRNA technology has ever received authorization for use in a vaccine. Moderna’s vaccine received Emergency Use Authorization from the U.S. Food and Drug Administration (FDA) on December 18.
“Every single one of the clinical trial participants who received the Pfizer vaccine is thought to have made antibodies against SARS-CoV-2,” which causes COVID-19, says Dr. Palese, who has dedicated his career to the study of vaccinology. Even the 5 percent of participants who did not make enough antibodies to be fully protected made enough to be partially protected against severe disease, he adds. “That is success and that is why everyone is so excited. I hope everyone who is eligible gets vaccinated.”
Like most scientific advances, mRNA technology has evolved over decades. When the COVID-19 pandemic hit in early 2020, mRNA was ready for prime time. The technology was first used successfully in mice in 1990. But it was an unstable molecule that could not be easily transferred into the human body. Over time, improvements in nanoparticle technology enabled mRNA to overcome that hurdle.
This chart shows how messenger RNA vaccines work.
In 2017, mRNA’s safety and efficacy in humans was reported in The Lancet, in a clinical trial of a rabies vaccine. The same year, early human trials began for an mRNA-based Zika virus vaccine. The technology is also being tested for use in cancer vaccines that are now in clinical trials around the world, some in combination with chemotherapy, radiotherapy, and immune checkpoint inhibitors.
Today, synthetic mRNA can be quickly manufactured in a laboratory and engineered to resemble fully mature mRNA molecules that occur naturally in the cytoplasm of the eukaryotic cells of animals. The platform works like a software program that carries the genetic code of the spike protein, an important and easily recognizable portion of SARS-CoV-2. When the code—delivered in a nanoparticle—is injected, the human body begins to make antibodies that recognize and protect against the virus.
The mRNA technology is considered particularly safe since its footprint is so minimal. It does not require the development of inactivated pathogens or small units of inactivated pathogens to trigger an immune response, which is the case with traditional vaccines. In addition, mRNA does not enter the cell nucleus where a human’s genetic material, or DNA, is kept, and leaves the body as soon as it has finished delivering its code. Its main drawback, however, is its high cost due to the intricate lipid preparation of the nanoparticles and the extremely low temperature required to store the vaccines.
Peter Palese, PhD
“If you have mayonnaise and you let it stand, it separates and you get this oily phase,” Dr. Palese says. “It’s the same thing with the mRNA vaccines: they get oily and separate.” The Pfizer and Moderna vaccines require slightly different storage temperatures because they use different lipid particles.
“No shortcuts were taken in the actual scientific development of these vaccines, and we have enough data to know how well they work,” says Dr. Palese. The quick pace of development—which essentially compressed the 10 years it typically takes to develop a vaccine into 10 months, combined with massive amounts of funding—enabled the mRNA vaccines to reach the finish line in record time. Dr. Palese says the closest comparison to such large-scale production took place during World War II during the Manhattan Project, when the United States, the United Kingdom, and Canada joined forces to create nuclear weapons.
In 2020, billions of dollars were provided by the U.S. government, European governments, major corporations, and private donors to fund COVID-19 vaccine development, which, he adds, employed tens of thousands of “really smart people” who were focused on creating safe and successful vaccines.
Dr. Palese expects successful vaccines that use conventional methods will not be far behind those based on an mRNA platform. Within the Icahn School of Medicine at Mount Sinai’s Department of Microbiology, he and his colleagues Adolfo García-Sastre, PhD, and Florian Krammer, PhD, are working on a COVID-19 vaccine that uses an engineered Newcastle disease virus vector. They expect to begin a phase 1 safety trial in January. Dr. García-Sastre is Director of the Global Health and Emerging Pathogens Institute, and Dr. Krammer is Mount Sinai Professor in Vaccinology.
While immediate and widespread COVID-19 vaccinations will help get humanity through the current crisis, scientists fear that SARS-CoV-2 will forever co-exist with humans the same way other infectious pathogens do.
If proven effective, Dr. Palese says Mount Sinai’s low-cost vaccine might be advantageous for use in low and middle-income countries and in young children and infants, who were not part of the mRNA vaccine clinical trials. “Vaccines are good for us,” he says. “They have helped save millions of lives.”