Simple Indicator Ensures Ultracold Supply Chain for mRNA Vaccines

Simple Indicator Ensures Ultracold Supply Chain for mRNA Vaccines


The COVID-19 pandemic, caused by the coronavirus SARS-CoV-2, continues to affect many countries. Vaccines based on messenger RNA (mRNA) can help fight the pandemic. However, they require ultracold storage: –70 °C and –20 °C for two widely used mRNA vaccines. These temperatures have to be maintained during transport and distribution, up until shortly before injection, for the vaccines to remain effective.

Sung Yeon Hwang, Dongyeop X. Oh, Jeyoung Park, Korea Research Institute of Chemical Technology (KRICT), Ulsan, and University of Science and Technology (UST), Daejeon, both Republic of Korea, and colleagues have developed a tamper-proof time-temperature indicator (TTI) for mRNA vaccine vials that can alert health care workers if the ultracold supply chain has been interrupted. The affected vials can then be discarded. To create the TTI, the team added a mixture of ethylene glycol, water, and blue dye to a small tube and froze it in liquid nitrogen. Then, they added a white cellulose absorbent to the top of the frozen coolant, turned the tube upside down, and adhered it to a larger glass vial containing a simulated vaccine at –70 °C.

At temperatures above –60 °C, the glycol/water mixture melts, and the dye diffuses into the white absorbent, turning it light blue. The color change happens about two minutes after the simulated vaccine is exposed to the higher temperature. Importantly, exposures of less than two minutes––which are unlikely to impair vaccine efficacy––do not turn the absorbent blue. The color change of the absorbent persists if the tube is refrozen at –70 °C, ensuring an unbroken ultracold supply chain. According to the researchers, the TTI could be tailored to monitor the ideal storage temperatures of different mRNA vaccines by changing the solvent/water mixture, its mixing ratio, or the absorbent.

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