Five years before Wuhan obtained notoriety as the epicenter of the COVID-19 pandemic, a four-year-old child in central China contracted polio from an unknown source. Somewhat unexpectedly, researchers in Paris have now linked this infection to a poliovirus (PV) strain that has been used for research purposes since the 1950s, and may therefore have escaped from a laboratory before coming into contact with the unfortunate youngster.
Before going any further, it’s important to point out that the study authors are not definitively claiming that this case was the result of a lab leak, as there simply isn’t enough data to determine how the infection occurred. Furthermore, while the child’s virus was analyzed and sequenced at the Wuhan Institute of Virology (WIV), there’s no evidence to suggest that the pathogen originated in the city, or even in China.
The researchers made their discovery as they prepared to destroy four PV strains that had been stored at the Pasteur Institute in Paris since 1960. Before erasing the pathogens, the study authors sequenced their genomes, revealing that one of the quartet – known as Glenn – was more than 95 percent identical to the polio strain that infected the Chinese child back in 2014.
Known as WIV14, the young patient’s virus was previously studied by researchers at WIV, who concluded that it had probably evolved from a strain called Sabin 3, which is used to make oral polio vaccines. However, the authors of the new study find this unlikely, since WIV14 appears to share a very recent common ancestor with Glenn.
This revelation led them to a strain called Saukett A, which was first isolated in the US in the 1950s and bears a resemblance to both Glenn and WIV14. The study authors therefore decided to sequence the full genome of Saukett A, revealing that it was more than 99 percent identical to the strain contracted by the child in Wuhan.
In other words, the 2014 infection appears to have been caused by a PV strain that was circulating sixty years earlier. According to the researchers, such a scenario can only occur if this pathogen happened to be “released from a natural reservoir in which it had lain dormant for decades or from a facility.”
And while the permafrost could in theory provide such a reservoir, the authors say it’s suspicious that this particular case involves a strain that has been “handled by dozens of factories around the world to make the [injectable polio vaccine].”
“Therefore, the hypothesis of a leak from a facility cannot be ruled out,” they write.
Discussing how this may have occurred, the researchers go on to explain that “regulations regarding PV containment” were only tightened up in the 2010s, and that prior to this point, “PVs were widely used for multiple purposes, such as basic researches, educational activities, or validation of disinfectants.”
“It is therefore possible that several undocumented PV leaks occurred in the past from facilities handling PVs, especially when PVs were considered as low-risk viruses due to the existence of vaccines,” they continue.
Ultimately, the authors are unable to trace the origins of WIV14, which they say remain “unidentified,” although they conclude that it could have “emerged after a PV strain released anywhere in the world had circulated before being sampled in China.”
The study has been published in the journal Virus Evolution.
