The action was innocent: While cleaning the Veterans Affairs hospital in Boston this past January, a contractor knocked a loose freezer plug from its socket. This simple mistake resulted in the loss of nearly 2,000 doses of Moderna’s COVID-19 vaccine that had been chilling inside the unplugged appliance. While that’s a small hit on the grand scale of worldwide vaccination, it’s emblematic of a much larger issue for many COVID-19 vaccines; they have to be kept frozen.
Two of the major coronavirus shots authorized for emergency use in the United States—the Moderna and the Pfizer/BioNTech vaccines—rely on a costly series of temperature-controlled shipments and storage, known as the cold chain, to get vaccines from manufacturers to muscle injection. Such stringent temperature requirements also pose an obstacle for equitable vaccine distribution, increasing the cost and difficulty of shipments and cutting off access to remote communities without reliable electricity or refrigeration.
The reason for these frigid conditions is that the key vaccine ingredient—a molecule called messenger RNA (mRNA)—is extremely fragile and storage at cold temperatures slows down the chemical reactions that can tear it apart. But promising efforts to reduce this frosty burden are already in the works—from tinkering with the mRNA structure to shipping the vaccine in solid form with a sugary protectant.
Such efforts are not just important for halting the current pandemic. Scientists see promise in mRNA vaccines for treating a wide variety of other diseases, since they can be readily tweaked for different viral variants as well as rapidly developed for new viruses.
“All those steps that are taken now will be really important in the coming years,” says Rein Verbeke, a pharmaceutical scientist specializing in mRNA vaccines at Ghent University in Belgium.
The necessity for cold storage lies at the heart of how these vaccines work, which is mRNA. These strands of genetic code in the COVID-19 vaccine carry instructions that the human cell uses to manufacture the characteristic spike protein, which sits on the surface of SARS-CoV-2. This preview of the protein familiarizes the body’s immune system with the virus so that it can recognize and fight future coronavirus invaders.