Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), the virus responsible for COVID-19, exhibits considerable stability in diverse environmental conditions. Freezing temperatures do not eliminate the virus. Instead, cold environments significantly slow the natural decay process, allowing the virus to remain infectious for extended periods.
The Direct Answer: Stability in Cold Temperatures
The virus is highly resilient to temperatures typically found in home freezers, which hover around -20°C (-4°F). Studies show that SARS-CoV-2 can maintain its infectious potential for weeks, and sometimes months, when stored at these temperatures. Freezing effectively preserves the virus rather than destroying it, similar to how biological samples are kept viable in a laboratory.
Temperatures used for ultra-cold storage, such as -80°C (-112°F), are routinely employed in research laboratories for the long-term cryopreservation of viruses. This practice confirms that extreme cold is a mechanism for stability, not inactivation. Even repeated cycles of freezing and thawing have been shown to have no significant effect on the virus’s ability to remain viable and infectious in laboratory samples.
The Science Behind Viral Freezing Survival
SARS-CoV-2 is an enveloped virus, meaning its genetic material is encased in a protective layer composed of a lipid membrane, which is a fatty outer shell. This lipid bilayer is the virus’s primary defense against environmental stressors, and it is the target of common soap and detergent molecules.
When the virus is subjected to low temperatures, the degradation processes that would normally break down its structure and genetic material (viral RNA) are dramatically slowed or halted. Temperature acts as a pause button for biological decay. The surrounding matrix, such as proteins and salts in human secretions or food matter, can also provide a buffer that shields the virus from temperature fluctuations and physical damage.
The lipid envelope of the virus remains intact in the frozen state, protecting the internal RNA from degradation, which is a process that accelerates at warmer temperatures. This means that while the virus is not active or replicating in the freezer, its structural integrity is maintained. Upon thawing, the virus can potentially regain its infectious capability, provided the delicate spike proteins on its surface, necessary for cell entry, have not been denatured.
Practical Risks and Transmission Pathways
The stability of SARS-CoV-2 in cold environments has practical implications, particularly concerning the movement of goods along the global “cold chain.” Transmission is a concern on surfaces and packaging maintained at refrigerator or freezer temperatures during transport and storage. Studies have shown the virus can survive for at least 30 days on frozen food surfaces, including beef, chicken, and salmon, at standard freezer temperatures of -20°C.
While the primary mode of transmission remains person-to-person respiratory contact, contact with contaminated frozen items or their packaging is a plausible pathway. The environment on frozen foods, particularly those with high salt content like seafood, can help stabilize the virus and prolong its survival. Consumers handling items taken directly from a cold storage facility or freezer should be mindful of the potential for surface contamination, as the cold temperature preserves any viral particles present.
Deactivating the Virus
Since freezing is a preservation method rather than a deactivation method, specific steps are necessary to eliminate the virus on items and surfaces. For frozen food products, applying high heat is the most reliable method for deactivation. Cooking food to safe internal temperatures, typically above 70°C (158°F), will rapidly destroy the virus by denaturing its proteins and dissolving its lipid envelope.
For surfaces and packaging, chemical deactivation is an effective strategy. Common household disinfectants, such as those containing sodium hypochlorite (bleach) or ethyl alcohol (at concentrations of 60% or higher), disrupt the viral structure. Simple soap and water are also highly effective, as detergent molecules dissolve the fatty lipid membrane. Practicing good hand hygiene after handling frozen groceries or food packaging remains the most effective way to mitigate surface-related risk.