Cold-Chain Storage: What to Freeze, What to Store at Room Temperature

Cold-Chain Storage: What to Freeze, What to Store at Room Temperature


As the world continues to roll out aggressive COVID-19 vaccine initiatives, an even larger focus is being placed on the evolution of mRNA research. With major advances in biopharmaceutical technology, it fueled a need for sophisticated cold storage options. Purchases of ultra-low freezers exploded in real-time, and it had sort of an unsuspected ripple effect for those in the research industry. They needed to quickly create a strategy for housing large-scale vaccine product lots and other biologics used in the scope of research. For large manufacturing projects, biorepositories can be advantageous.

However, it does not eliminate the need for localized clinical-based cold storage solutions. Many of the mRNA-based biologics require subzero temperatures to remain viable. For many of the smaller vaccine distributors (Walgreens, Rite Aid, etc.), having a laboratory-grade ultra-low freezer onsite was not the norm. The volatile nature of the COVID-19 vaccines led to many of these types of clinical outfits scrambling to invest in ULT freezers just to meet vaccine housing objectives put in place by the pharmaceutical manufacturers. Staff also had to go through somewhat of a daunting learning curve to figure out which biologics are safe at room temperature or even refrigerated temperatures.

Because of the expense of medical-grade freezers, there are those who wonder about using non-medical units for their cold storage needs. Household and commercial-scale refrigerators and freezers are discouraged for use in laboratories. Even though some of the newer stainless steel residential models look sturdy and capable, they are not designed to maintain consistently low temperatures when doors are opened to place or retrieve samples. It makes purchasing medical-grade freezers worth the expense because the cost of wasted samples due to incorrect temperature storage is far greater.

How Do ULT Freezers Differ from Standard Laboratory Grade Freezers?

The main difference between laboratory-grade refrigerators and freezers is operating temperatures. These types of scientific–grade models are classified by the terms medical refrigeration, low-temperature freezers, and ultra-low freezers and are further distinguishable by their capacity, orientation, and available temperature ranges:

  • Medical refrigerators typically operate from 2 °C to 10 °C and the freezers from –25 °C to –10 °C.
  • Low-temperature freezers are available for temperatures of –25°, –30° and –40 °C.
  • ULT (Ultra-low freezers) operate and range between -45°C. and –86°C.

ULT freezers typically come in four different orientations:

  • Upright
  • Chest
  • Undercounter
  • Countertop

ULT freezers are constructed with heavily insulated walls designed to maintain interior temperature stability. They usually operate with a cascade refrigeration system, which uses two compressors paired with specific refrigerants with low toxic footprints. The refrigerants used in ULT freezers are comprised of gaseous compounds that transform easily into a liquid. These compounds (propane and ethanol) have predictable evaporation temperatures, which is important to the cooling process.

The inner workings of each ULT model may vary, but the intent is the same – to deliver consistent ultra-low temperatures without interruption. Because maintaining temperature is the most important concern with biobanks and other related clinical operations, product temperature sensors and battery backups are used to help safeguard the biological contents. Since there is often a variation in product content and surrounding air pockets, product sensors avoid unnecessary temperature alarms triggered by routine door openings. Usage of the ULT freezer paired with optimized temperature monitoring tools all play a key role in avoiding major interruptions within the pharmaceutical cold chain.

Why Do Vaccines and Other Biologics Require Ultra-Low Cold Storage?

The biologics used in the R&D clinical space are used to treat a wide variety of health conditions such as cancer, chronic disease, genetic anomalies, environmental illnesses, viruses, and more. Many of these pharmaceuticals require ULT freezer storage ranging from –45° and below, as in the case of the COVID-19 vaccines. The ultra-low temperatures help to preserve the efficacy of a given biological product by slowing down molecular changes that naturally occur in time in warmer temperatures.

ULT freezers are designed for delicate molecular-based samples containing DNA from a variety of sources, including:

  • Blood (specifically white blood cells)
  • Semen
  • Human, animal, and microbial cells
  • Urine
  • Plasma
  • Organ tissue

Certain biological specimens, reagents, assays, and organic tissue samples, require ultra-low temperatures because their molecular components are extremely sensitive to temperature changes. When the temperatures hover out of optimal ranges, nucleic acids, proteins, and other molecular matter begin to deteriorate and break down. In some instances, even a slight thaw and re-freeze cycle can result in unknown changes to the complex protein structure of biologics, resulting in decreased immunogenicity and bioavailability.

An article in Smithsonian Magazine recently spoke directly to the fragility of mRNA-based vaccines and why even the slightest temperature variances can lead to a costly mishap.

The biotechnology companies have made some modifications to the mRNA’s molecular structure to make it more stable. Then, they used nanoparticles of fatty molecules called lipids to wrap up the mRNA, sort of like bubble wrap around a fragile item in the mail. Enzymes called ribonucleases destroy mRNA, and they “are everywhere, even in the controlled environment of the lab,” says Infectious Disease Research Institute vaccine development specialist Alana Gerhardt to Science magazine's Jocelyn Kaiser.

In another instance, a 2016 Dutch-led observational study found similar temperature variances led to questions about the decreased treatment efficacy in their patients. It is widely accepted and supported by many clinical studies that when biologics fall out of alignment with their recommended temperatures, unknown changes can occur at the drug’s molecular level. This can result in adverse effects and/or patient fatalities.

Can You Store Multiple Sample Types in the Same Cold-Storage Unit?

Many biologics can be stored in the same cold/storage unit, especially if the unit has the capabilities for multi-compartmental zoned temperatures. However, the general rule of thumb is to first organize biologics by their respective cold-storage recommendations.

What industry experts know about vaccine quality and maintaining the cold chain is that a good set of SOPs (standard operating procedures) can’t be stated enough. This helps break down the burden of responsibilities among manufacturers, distributors, public health staff, and health care providers.

Success in laboratory operations with regard to cold-chain adherence depends upon three crucial elements:

  • Consistent training efforts for laboratory staff
  • Reliable medical-grade refrigeration/freezer and temperature monitoring equipment
  • Solid Inventory management

Another factor that plays a role in the successful management of cold storage is a comprehensive understanding of the biologics contained in the inventory. For example, the recent COVID-19 vaccine roll-out had two distinct cold storage requirements.

Store vaccine vials upright in the tray and protect them from light. Before mixing, the vaccine may be stored in an ultra-low freezer between -90°C and -60°C (-130°F and -76°F).

  • The Moderna vaccine product has the following cold storage recommendations:

Unpunctured vials should be stored in a low-temperature freezer between -50°C and -15°C (-58°F and 5°F). Store in the original carton. Protect from light. Do not store with dry ice or below -50°C (-58°F)

How Do You Know Which Biologics Should Be Kept in the Freezer, Refrigerator, or Room Temperature?

For consumers, there is a list of commonly prescribed medications that have specific cold storage recommendations. These are normally provided for patient self-monitored type prescriptions such as insulin. For patients with inflammatory rheumatic diseases, the concerns of proper cold storage considerations at home were even addressed in a clinical study.

A professional clinical space must be prepared to house thousands of samples at any given time. In some situations, the number of biologics can be expansive. It can be challenging to organize, label, inventory track, and store correctly. Labs that work with large sample volumes should look for ULT models that feature compartments fitted with individual specimen racks to help separate sample types.

What Sample Types Can Be Stored at Room Temperature Storage (15ºC to 27ºC)?

While room temperature storage is not the norm for molecular-based samples, there are exceptions. For instance, it is possible to retrieve DNA results from preserved or dried tissues that have been kept at ambient temperatures, like FFPE (fixed formalin paraffin tissues). Biorepositories typically hold massive quantities of FFPE samples in climate-controlled rooms designed for optimizing sample longevity. However, the DNA in these tissues degrades quickly and, in most cases, only yields partial readings. RNA is highly volatile at room temperature and most often cannot be separated from tissues that have not been kept in freezer storage.

What Biologics Are Better Maintained in Refrigerated Short-Term Storage (2ºC to 5ºC)?

Refrigerated temperatures are best suited for the short-term storage of frequently used biological reagents, such as enzymes and antibodies. These reagents deteriorate rapidly if repeatedly frozen and thawed. Laboratory best practices suggest taking what is needed for experimentation and then the remainder of the sample is to be frozen until needed, reducing the number of freeze-thaw cycles that may result in compromised product integrity.

What to Place in Freezer Storage (-20ºC)

-20ºC freezer storage is recommended for short-term storage of temperature-reactive samples and reagents. DNA and RNA can be obtained from tissues that have been suspended in preservative solutions before freezing at -20ºC. However, in the absence of a stabilizing solution, ultra-low temperatures are best for long-term storage of cellular-based tissues and samples.

Ultra-low Freezer Storage (-80ºC) is Recommended for Vaccines and Biologics

Ultra-low temperatures help stave off premature degradation of sensitive molecules and biologics such as those contained in mRNA vaccines. Low-temperature housing is shown to preserve the viability of both biological assays and reagents. For samples that are housed routinely in ULT freezers, it is important to follow the recommended freeze-thaw protocols.

Cryogenic Freezer Storage (-150ºC to -190ºC)

Cryogenic temperatures are ideal because they bring all naturally occurring biological processes to a halt. Cryogenic storage is recommended for storing specimens that are not suspended in a preservative-based solution. Because of this, cryogenic storage is considered the gold standard for long-term storage. Like ultra-low temperature freezing, it is important to consider freezing and thawing protocols when opting to use cryogenic freezer storage.


We understand the concerns of our scientific partners and the many considerations that go into making ideal storage temperature decisions for biological materials. As we help take some of the guesswork out of cold-storage recommendations, we know the best results come from following the outlined recommendations by the manufacturer. This helps to maintain product viability. The margin for error is exceedingly narrow when it comes to housing precious life-saving vaccines, reagents, tissues, platelets, and other blood products.

In many ways, The COVID-19 pandemic helped put our scientific community in the spotlight as they work hard to find new therapeutic treatment solutions for this deadly virus. This meant quick solutions were being made and ongoing tweaks to the logistical conundrum experienced by an ill-prepared cold-chain system.

Because there is so much at risk, K2 Scientific understands where quality, necessity, and value intersect. Our goal is to help provide the best cold storage solution for future analytical or research projects. Contact a team member today for more information on our bestselling laboratory-grade refrigeration and freezers.

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