Vaccines for COVID-19 have been created by researchers at record speed. The first two vaccines distributed largely in the United States are mRNA-based and necessitate ultracold storage (−20°C for one and −70°C for the other).
Scientists have now designed a tamper-proof temperature indicator that can warn health care workers when the temperature of a vial of vaccine reaches unsafe levels for a specific period, which could facilitate the distribution of effective mRNA vaccines. The temperature indicator has been described in the ACS Omega journal.
Both the COVID mRNA vaccines include instructions for developing harmless portions of the SARS-CoV-2 spike protein.
Upon injecting the vaccine into the body, the mRNA instructions are used by human cells to create the spike protein, which is temporarily displayed on their surface, thus activating an immune response.
However, mRNA is extremely unstable and necessitates ultracold storage and transport conditions to enable the vaccines to stay effective.
Sung Yeon Hwang, Dongyeop Oh, Jeyoung Park, and their collaborators intended to create a time-temperature indicator (TTI) to detect mRNA vaccines exposed to unsuitable temperatures during storage or transport, so that they can be discarded.
The researchers developed their TTI by adding a mixture of ethylene glycol (antifreeze), blue dye and water to a small tube, which was then frozen in liquid nitrogen. A white cellulose absorbent was then added to the top of the frozen coolant, the tube was turned upside down, and it was attached to a larger glass vial with the simulated vaccine at −70°C.
When the temperatures reached more than −60°C, the antifreeze mixture starts melting and the dye starts diffusing into the white absorbent, converting its color into light blue.
The change in color occurred nearly 2 minutes following the exposure of the simulated vaccine to a higher temperature. Most significantly, exposures of less than 2 minutes—which are not likely to affect vaccine efficacy—did not change the TTI blue.
The color change lasted when the tube was refrozen at −70°C, thus making the system tamper-proof. According to the researchers, the TTI can be customized to detect the optimal storage conditions of various mRNA vaccines by varying the coolants or their mixing ratio, or by using different absorbents.
Hao, L. T., et al. (2021) Tamper-Proof Time–Temperature Indicator for Inspecting Ultracold Supply Chain. ACS Omega. doi.org/10.1021/acsomega.1c00404.