Did the virus come from frozen food? The idea is being investigated, but the science is far from clear

---

Did
the
virus
come
from
frozen
food? 
The idea is being investigated, but the science is far from clear
COULD the virus that caused a worldwide pandemic have made the jump 
to humans via frozen food? That was one hypothesis put forward on 9 
February by a joint World Health Organization and Chinese investigation 
into the origins of SARS-CoV-2.
Frozen animals were found on sale at Huanan market in Wuhan, China, 
the place where the virus was initially detected, the team behind the 
inquiry said. In a press conference, Peter Ben Embarek, the head of the 
investigation, said: “We know the virus can survive in conditions that are 
found in these cold, frozen environments, but we don’t really understand 
if the virus can transmit to humans.”
The idea that the coronavirus was carried inside or on the surface of 
frozen food, which has been advanced by Chinese state media, could place 
the source of the virus beyond China, in an animal imported from another 
country.

---

Yet it is far from clear whether the virus could survive in an infectious 
form in frozen food. “I would say it’s extremely, extremely unlikely the 
virus would have spread through that type of route,” says Lawrence 
Young at the University of Warwick, UK, who specialises in human 
virology. The reason why, according to Young, is that SARS-CoV-2 is 
an enveloped virus, meaning it is covered with a fatty, lipid membrane 
that is integral to its ability to infect human cells. This membrane is very 
vulnerable to cycles of freezing and thawing, as can happen during the 
transit and sale of frozen food. Stripped of this envelope, such viruses 
can’t infect people.
Workers package frozen steak at a beef-processing plant in Binzhou, 
China
A review by Jie Han and Zue Zhang at Xi’an Jiaotong University in Shaanxi, 
China, and their colleagues of evidence on spreading the coronavirus 
via food concluded that “major knowledge gaps exist” on the role that 
frozen food plays. “Data are lacking on the long-term survival of SARS-
CoV-2 under freezing temperatures (-10°C to -20°C) that are frequently 
encountered on the storage and transport of frozen foods,” the team 
wrote.
Just one study, which hasn’t been peer reviewed, has tried to obtain that 
data. Dale Fisher at the National University of Singapore and his 
colleagues put the virus into cubes of pork, chicken and salmon, finding 
no decline in the viral load after 21 days in a lab at a refrigeration 
temperature of 4°C or at a standard freezing temperature of -20°C.
However, from this experiment, it isn’t clear whether the viral load was 
still infectious to humans. In addition, the experimental parameters may 
not reflect real-world viral loads or conditions in food supply chains.
SARS-CoV-2 may have a rough time when frozen food is transported. 
During air travel, for instance, temperatures drop to between -20°C and -
30°C in cargo holds when planes are airborne, then rise much higher after 
landing.
“
I would say it’s extremely, extremely unlikely the virus would have 
spread via frozen food”
By ship, the virus could suffer from the “salty air issue”, in which salt 
levels in the air can affect the number of viruses that can survive, says 
Julian Tang at the University of Leicester, UK. Changes in humidity on 
frozen

---

food’s journey may also negatively affect SARS-CoV-2, as the lipid 
membrane can be disrupted by taking on fluid from the air.
We do know that the virus has been found to persist on the packaging of 
frozen food. After two workers at Qingdao Port in China tested positive 
in September 2020, SARS-CoV-2 was found on 50 of 421 samples of frozen 
cod packaging.
However, Rodney Rohde at Texas State University says that despite the 
virus being found on packaging, it doesn’t mean it is in a viable state that 
could infect our cells. “One must remember that any viral genetic material 
may be found on all types of surfaces, including frozen surfaces. But 
molecular PCR tests [that identify the presence of the virus] do 
not differentiate ‘viable’ from ‘non-viable’ virus.”
The other possible route is if the virus is transported inside the frozen 
meat or fish itself. “If it’s part of the meat, it has more protection,” says 
Tang. Even if the virus was still in an infectious form by the time it 
reached a person in Huanan market, there are still questions over how 
they were actually infected. Cooking the meat would kill the virus, as 
would the gastric acid in our stomachs, says Young. However, if the food 
was raw or not properly cooked, people could potentially be infected from 
surfaces during food preparation or via the upper respiratory tract while 
chewing the food.
“
Overall, the probability [of infection via frozen food] is low. [But] if it 
happens once – a one-in- a-million event – and it’s enough to seed the 
virus in the human population, you might get that spread,” says Tang.