It's true for practically every virus that they are viable for longer at lower temperatures. Unless they are cultured, storing [freeze dried] viruses below -20C is the only way to keep them viable for decades. (More typically they are held below -70C as a safety margin.)
The ability to store viruses for long periods of time with minimal loss of viability is critical [well, for research]. Even more than most organisms, many
viruses are fragile and degrade quickly unless stored at low temperatures. The ATCC® and BEI Resources collections offer a
unique opportunity to study the stability of various viruses under different conditions. The ATCC® Virology Collection, which
celebrates 50 years of operation in 2008, contains more than 2,500 different holdings spanning decades of storage time using
many different storage methods. A retrospective study was performed to evaluate the short and long-term viability of various
holdings of influenza virus within the ATCC® collection, using virus stocks that had been grown and titered as long ago as 1968 (40
years) up to as recently as 2007 (3 months). Influenza and parainfluenza viruses prepared from 1968 to 1992 were either in liquid
form or were lyophilized, while preparations after 1992, were only stored in liquid form at -70°C or in vapor phase of liquid nitrogen
(approximately -125°C). In addition, a prospective study was performed by holding viruses at -80°C, -20°C, 4°C, room temperature
(~20°C) and 37°C for various lengths of time with periodic re-titration. All testing was performed in specific pathogen free
embryonated chicken eggs in order to obtain the 50% chicken egg infectious dose (CEID50 ). Titers were then plotted and rate of
decay (log of titer loss per unit time - D10 values) was calculated. When stored at -20°C, -70°C or in liquid nitrogen, most influenza
and parainfluenza viruses maintained viability with no significant loss of titer over the study period. One influenza isolate was seen
to lose approximately 1 log of titer over a 16 year period when stored at -70°C. This drop in viability opens the possibility of strain-to-strain differences in storage. Viruses stored at temperatures above -20°C showed a direct correlation between temperature and
decay rate, with the virus stored at 37°C having the highest rate of decay. From these data, we conclude that of the various
methods employed at ATCC® and BEI Resources for the storage of virus preparations, storage in liquid form in the vapor phase of
liquid nitrogen offers the benefits of simple, safe storage and excellent recovery [...]
An ancient giant virus was discovered in permafrost in 2014; it's estimated it had remained viable for 30,000 years.
Two years ago, Claverie and Abergel's team learned that scientists in Russia had resurrected an ancient plant from fruits buried in 30,000-year-old Siberian permafrost. “If it was possible to revive a plant, I wondered if it was possible to revive a virus,” says Claverie. Using permafrost samples provided by the Russian team, they fished for giant viruses by using amoebae — the typical targets of these pathogens — as bait. The amoebae started dying, and the team found giant-virus particles inside them.
More relevantly, there have been such cases of viruses dangerous to us, like hepatitis or norovirus being found e.g. in frozen berries.
Frozen berries are used as ingredients in many foods and like other produce can be an important part of a healthy eating pattern. While frozen berries are used in pies and other baked goods, they are also used raw in fruit salads or smoothies and have been associated with outbreaks of foodborne illness. The FDA reported three hepatitis A virus outbreaks and one norovirus outbreak linked to frozen berries in the United States from 1997 to 2016.
But note that we didn't abandon using fridges for our food for this reason (that viruses are viable for a long time once frozen)...
In particular, since you mentioned Covid-19 outbreaks at meat factories, we usually cook meat before eating it, so most dagner is probably to factory workers rather than consumers. So far the FDA has not reported any outbreaks/clusters of Covid-19 as being caused by food sources. Additionally, they mention that
Unlike foodborne gastrointestinal (GI) viruses like norovirus and hepatitis A that often make people ill through contaminated food, SARS-CoV-2, which causes COVID-19, is a virus that causes respiratory, not gastrointestinal, illness. Foodborne exposure to this virus is not known to be a route of transmission.
