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Scientists have been developing COVID-19 vaccines with record speed. The first two vaccines widely distributed in the United States are mRNA-based and require ultra-cold storage (-70 C for one and -20 C for the other). Now researchers are reporting ACS Omega have developed a tamper-evident temperature indicator that can alert health workers when a vaccine vial reaches an unsafe temperature for a certain period of time, which could help ensure the distribution of effective mRNA vaccines.
Both COVID mRNA vaccines contain instructions for making harmless pieces of the SARS-CoV-2 spike protein. After the vaccine is injected into the body, human cells use the mRNA’s instructions to make the spike protein, which they temporarily display on their surface, triggering an immune response. But mRNA is very unstable, requiring ultra-cold storage and transport conditions for vaccines to remain effective. Sung Yeon Hwang, Dongyeop Oh, Jeyoung Park and their colleagues wanted to develop a time-temperature indicator (TTI) to identify mRNA vaccines that are exposed to unwanted temperatures during storage or transport, so that they can be discarded.
To make their TTI, the researchers added a mixture of ethylene glycol (antifreeze), 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 glued it to a larger glass vial containing a simulated vaccine at -70 C. At temperatures above -60. C, the antifreeze mixture melted, and the dye diffused into the white absorbent, making it light blue. The color change occurred about 2 minutes after the sham vaccine was exposed to a higher temperature. It is important to note that exposures of less than 2 minutes –– which are unlikely to affect the effectiveness of the vaccine –– did not turn TTI blue. The color change persisted if the tube was refrozen at -70 C, rendering the system tamper-proof. By changing the coolants or their mixing ratio, or using different absorbents, the TTI could be adapted to monitor the ideal storage conditions for different mRNA vaccines, the researchers say.
Reference: Hao LT, Lee M, Jeon H et al. Tamper-evident time-temperature indicator for ultra-cold supply chain inspection. ACS Omega. 2021; 6 (12): 8598-8604. doi: 10.1021 / acsomega.1c00404.
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