Why some mRNA products need ultra-cold storage
mRNA is a fragile molecule and is delivered in lipid nanoparticles that are themselves sensitive to temperature. Lower temperatures slow the chemical and physical changes that reduce potency. For some products, that means ultra-cold storage for the long term and a defined, shorter period in a refrigerator before use.
Formulations change over time, and newer versions of some products have broader storage conditions. Never assume one product's rules apply to another, or that last year's label applies to this year's batch.
What a label can look like
As an example of how these conditions are expressed, the US prescribing information for one widely used mRNA COVID-19 vaccine allows storage of frozen vials in an ultra-low temperature freezer at −90 °C to −60 °C, permits transfer to +2 to +8 °C for a limited number of weeks, prohibits refreezing after thaw and specifically says not to store vials at −25 °C to −15 °C. The US CDC's vaccine toolkit uses the same −90 to −60 °C band for ultra-cold freezers.
These details are given to show the structure of such labels — a frozen band, a refrigerated window, a no-refreeze rule — not as instructions.
Equipment involved
| Stage | Equipment | Key concern |
|---|---|---|
| Long-term storage | Ultra-low temperature freezer able to hold the label band | Margin below the upper limit; alarms; backup |
| Short-term or thawed storage | Pharmaceutical or vaccine refrigerator at +2 to +8 °C | Tracking the refrigerated window per batch |
| Transport and contingency | Qualified thermal shippers, sometimes with dry ice | Temperature evidence and handling safety |
| Monitoring | Loggers with probes rated for ultra-cold temperatures | Ordinary loggers may not read that low |
Monitoring at ultra-cold temperatures
Not every logger or probe works at −80 °C. Check the probe's rated range and the calibration points on its certificate — a certificate covering only +2 to +8 °C tells you nothing about accuracy at −70 °C. Buffered probes and cables must tolerate the cold, and the door seal must close properly around any probe lead.
Track two clocks per batch: time in the freezer and, once moved, time in the refrigerator against the label's refrigerated window. Record the transfer date on the carton or in your system.
Dry ice safety
- Dry ice turns into carbon dioxide gas, which can displace oxygen in small or poorly ventilated rooms; use it only in ventilated areas.
- Never seal dry ice in an airtight container — gas pressure can rupture it.
- Handle with insulated gloves to avoid cold burns.
- Do not put dry ice inside a refrigerator or ordinary freezer; it can upset the controls and the gas has nowhere to vent.
- Follow your institution's safety procedure and the shipper's instructions.
Practicalities for Indian sites
Ultra-low freezers put a lot of heat into the room and draw a high start-up current. In India that means a ventilated or air-conditioned room within the freezer's rated ambient, a dedicated earthed circuit, voltage protection and backup power that can carry the freezer's starting load. Check how the freezer behaves when power returns after a cut.
Have a contingency: space in another ultra-cold freezer, an arrangement with a nearby facility, or a dry ice supply, and a written plan that says who decides what happens to product after an excursion.
Where general deep freezers fit
KALT's deep freezer range reaches −60 °C. That is the upper edge of the −90 to −60 °C band used for some mRNA products and leaves no margin, so it should not be treated as an ultra-cold vaccine freezer. Choose equipment whose operating range sits well inside the label band, and confirm acceptability with your programme or regulator.
Frequently asked questions
- Can a −20 °C freezer hold mRNA vaccines?
- Only if the specific product's label allows that temperature. One widely used mRNA vaccine's US label specifically says not to store vials at −25 °C to −15 °C. Always follow the product's own storage statement.
- Do I need special loggers for ultra-cold freezers?
- Yes. The probe must be rated and calibrated for the temperatures you are measuring. A logger calibrated only around +2 to +8 °C can't prove accuracy at −70 °C.
