A medical worker takes samples on imported fish for COVID-19 nucleic acid test at a
refrigeration house in Lianyun district, Lianyungang, east China’s Jiangsu province, Aug. 11, 2021 (Photo by Wang Chun/People’s Daily Online)
Cold-chain products hold vital clues to the origins of COVID-19, and it’s very necessary to launch
global studies into the cold-chain transmission of the novel coronavirus, says an epidemiologist.
Such point of view echoes with a joint WHO-China study, which says the virus can be carried
long distances on cold-chain products.
Some of the earliest cases detected in Wuhan in December 2019 were linked to the Huanan
Seafood Market, where many shops were selling imported cold-chain products, and coincidently,
investigations found that imported cold-chain products were also the sources of the viruses in the
COVID-19 resurgences in Beijing, Dalian and Qingdao last year.
Studies indicate that the novel coronavirus can exist for weeks and even months in an environment
with a temperature between -1℃ and -10℃, and survive for years when temperature falls to -60℃.
“Transmission routes of COVID-19 are diverse. It can be transmitted through physical contacts, as
well as aerosols and droplets, and even contaminated matters,” said Ma Huilai, director of the
Chinese Field Epidemiology Training Program under the Chinese Center for Disease Control and
Prevention (CDC), warning that contaminated packages of cold-chain products might become a
hidden route for virus transmission.
Cold-chain products are generally stored and transported in low temperature, which offers
favorable conditions for the long-term existence of the novel coronavirus and constitutes a major
way of transmission, Ma noted.
The COVID-19 resurgence in Qingdao last October was an example, he said. Prior to COVID-19
cases resurged in the city, there had been five months during which none COVID-19 case was
reported.
According to Ma, the first two patients in Qingdao were material handlers moving cold-chain
products who had no history of traveling to other provinces or hospitalization. They had no
contact with foreign ship crew members whose nucleic acid tests showed negative. The only
possible scenario of infection was that they handled imported frozen gadus. Later, a high viral load
was detected in samples of the gadus, and the genetic sequence of the virus carried by the two
patients was identical with that on the packages of the frozen gadus.
In the first half of 2020, a number of enterprises around the world engaged in businesses relevant
to cold-chain products reported COVID-19 cases. These cases repeatedly proved that the virus can
be carried long distances on cold-chain products. Therefore, the COVID-19 cases in Wuhan’s
Huanan seafood market were very likely caused by imported cold-chain products.
The expert team that conducted the joint WHO-China study launched an investigation into the
imported cold-chain products at the Huanan seafood market and markets in downtown Wuhan.
According to Liu Jun, a researcher with the CDC and a member of the expert team, the ratio of
infections at the shops selling imported cold-chain products was much higher than that at other
shops, and the infection risk at these shops was 3.3 times higher.
All the earliest three patients at the Huanan seafood market were directly engaged in businesses
relevant to imported cold-chain products, and 16 of the 21 shops where the novel coronavirus was
sampled sold imported cold-chain products or were engaged in relevant businesses.
Liu said blood samples obtained before December 2019 in some countries were tested positive for
antibodies against the novel coronavirus, which meant COVID-19 infections might have happened
at that time. Some of the cold-chain products sold at the Huanan seafood market came from these
countries.
Besides, it is reported that horseshoe bats in some countries carry viruses similar to the novel
coronavirus, and some of the cold-chain products sold at the Huanan seafood market came from
these countries, too. Therefore, Liu believes it is necessary to launch a global origin tracing study
into the cold-chain industry.
Xu Wenbo, head of the National Institute for Viral Disease Control and Prevention under the
CDC, noted that where COVID-19 cases were firstly discovered doesn’t have to be the origin of
the virus. Origin tracing of COVID-19 is an issue of science that calls for cooperation among
global scientists, he said, adding that origin tracing in the cold-chain industry is of vital
importance.
Liu said international cooperation is very much needed by the origin tracing studies into the
imported cold-chain products sold at the Huanan seafood market in 2019. There were 678 shops at
the market, and 390 of them sold cold-chain products that totaled over 400 types from 37
countries, he explained.
It is necessary to carry out cooperation with the countries where these products were imported,
perform antibody test on the preserved blood samples of the people who then worked in the
industry, and trace their medical records, so as to find more clues to the true origins of the novel
coronavirus, Liu noted.
