In the early morning of August 16, a 41-year-old man in southwestern China’s Chongqing municipality got up and went for a jog beside a lake in a local open-air park — something that should have been a pleasant, if not unremarkable event. , outing. But what really happened during that 35-minute jaunt has now sparked international alarm and debate, with some scientists casting doubt on China’s startling account.
During his short run, the unmasked man infected 33 unmasked park visitors and two unmasked park employees with the coronavirus omicron subvariant BA.2.76, according to China’s Center for Disease Control and Prevention. The agency claimed the transfer occurred during casual encounters outdoors as he trotted past people on a four-metre-wide footpath. Many others became infected without any direct encounter. Twenty of the 33 infected park visitors became infected simply by visiting the outer areas of the park through which the jogger had previously passed, including an entrance gate. The two infected employees, meanwhile, quickly passed the infection on to four other colleagues, bringing the jogger park’s total outbreaks to 39.
To support these unusual conclusions, the CCDC cited case interviews, park surveillance footage and SARS-CoV-2 genetic data, which allegedly linked the cases but are notably absent from the report.
The claims in the report, if correct, would suggest that a major update is needed to our current understanding of the transmission risks of SARS-CoV-2. Although transmission outdoors is known to be possible, it is considered much less likely than indoor transmission, where virus particles can linger in stagnant air and accumulate over time in enclosed spaces. Transient outdoor encounters are especially not considered to be a significant risk, as massive amounts of moving air rapidly spread infectious doses of viral particles. For the same reason, it is believed that SARS-CoV-2 does not linger outside in menacing clouds in the wake of an infected person.
For now, experts outside of China are not revising their thinking about transmission risks, citing the report’s missing genetic data and other questionable conclusions.
Given China’s strict “zero COVID” strategy, the CCDC flatly dismissed the possibility that infections were part of an undetected outbreak in the wider community, calling exposure to the jogger (aka “patient zero”) the “only possible exposure” .
The CCDC claims that genetic data correlates all cases, showing that patient zero was the source of the 39 infections. Specifically, they report that 29 of the 39 cases “had the exact same gene sequencing as patient zero; 5 cases had a mutation site added to patient zero’s gene sequence; and the other 5 cases could not be sequenced due to unqualified copies.” ” But no sequencing data came with the report, and it’s unclear what sequencing was actually done to support their claims.
“If they had sequence data showing that 29 cases had identical genomes to ‘patient zero,’ that would suggest that all cases came from a single source,” virologist Angela Rasmussen told Ars. Rasmussen is a researcher at the Vaccine and Infectious Disease Organization at the University of Saskatchewan and affiliated with the Georgetown University Center for Global Health Science and Security.
“But,” she said, “it’s unclear if they sequenced the entire genome of all cases, what sequencing platform they used (Illumina vs Nanopore) etc.” The report only mentions ‘gene sequencing’, which may suggest only partial genome sequencing, not ‘whole genome sequencing’, which would certainly indicate a direct link between the cases. Without knowing the sequencing data and methods, it is impossible to confirm whether the jogger was the source.
The CCDC also offers a puzzling explanation of how jogging patient zero became infected in the first place.
According to the CCDC, the man became infected through a vague “exposure to contaminated aircraft environments”. The man had traveled from Chongqing to the northern city of Hohhot on Aug. 11 and flown back to Chongqing on Aug. 13 — three days before going for a jog. Neither flight had any known SARS-CoV-2 cases on board that could explain the man’s infection. But the plane he took for the return trip had carried four SARS-CoV-2 positive passengers the day before, on August 12.
On August 12, four passengers from Tibet took a plane from Chongqing to Hohhot and later tested positive in Hohhot. The plane, meanwhile, was not decontaminated after their flight, and the Chongqing man boarded the next day and sat (in seat 33K) near where three of the infected passengers had been (seats 34A, 34C, 34H). It is unclear how the man could have become infected in this way – SARS-CoV-2 is not known to remain airborne for that long, and transmission from contaminated surfaces is rare. In addition, the report does not indicate that other passengers on the flight were also infected, including people who actually sat in the same seats as the passengers from Tibet. But patient zero was infected with BA.2.76, which was circulating in Tibet, prompting the CCDC to make a link.
“I think it’s also very doubtful that ‘patient zero’ was infected on that plane,” Rasmussen said. “I noticed that the earlier flight with the passengers who were supposedly the source of the infection came from Chongqing – that could indicate a cryptic spread of BA.2.76 in Chongqing, not (only) Tibet, as the paper claims. In this case, if a whole group of people in Chongqing have BA.2.76, the sequencing data could point to a much larger outbreak in Chongqing, but you need the actual sequencing data to really figure out what’s going on hands.
“Basically, any claims about what the data actually shows depend on the actual inclusion of the data in the paper,” she said. “Otherwise it’s just speculation.”