Virologists explained how people act as a filter for COVID and change it.

New variants and strains of CORONAVIRUS emerge regularly because people themselves act as a "filter" for older variants of the virus. This was stated by Sergei Netesov, a virologist, academician of the Russian Academy of Sciences, and HEAD of the Laboratory of Bionanotechnology, Microbiology, and Virology at the Novosibirsk State University Natural Sciences Department, to RBC. He commented on the emergence of a new SARS-CoV-2 strain in Russia—XFG (Stratus). As of July 23, 114 cases had been registered; on August 23, Rospotrebnadzor reported 384 cases.

"New coronavirus variants have emerged before; they appear every three to four months and will continue to do so because the population becomes immune to the older variant, thus serving as a sort of filter for selecting new antigenically distinct variants," Netesov told RBC. He added that new coronavirus variants (such as Stratus, LP8.1, and LP1.8.1) emerge every three to four months. The scientist noted that this is a natural process associated with immune selection.

Omicron strains, which include Stratus, have an advantage, virologist, Moscow State University professor, and DOCTOR of Biological Sciences Alexey Agranovsky told RBC. "It evades antibodies present in the human population. Such variants emerge from time to time. Like other RNA-containing viruses, SARS-CoV-2 rapidly changes through mutations, and variants with the spike protein (S) can emerge, which antibodies in the bodies of those who have recovered from C-19 or who have been vaccinated recognize less effectively," he explained. "These variants gain an advantage and infect more people," he explained.

"Stratus" differs slightly from its predecessor, the JN.1 strain, Konstantin Chumakov, an adjunct professor at George Washington University and an advisor to the World HEALTH Organization, told RBC. "Its spike protein contains several mutations that slightly reduce its ability to be neutralized by antibodies to the older strain, which likely explains its rapid spread. However, this is insignificant, and previous vaccination remains effective. So this is a normal and expected process of viral evolution, but it does not have any serious clinical consequences," Chumakov said.

With new coronavirus variants, knowing the new strains isn't as important. "The 'Stratus' variant appeared in the EU and the US four to five months earlier, and it was replaced by two other variants, both still unnamed, one called LP8.1. And it's being replaced by LP1.8.1. These numbers mean nothing to anyone except specialists," Netesov told RBC. But if people haven't been sick in a while, they can, "most likely, easily recover from these variants, but their pathogenicity is virtually no different from previous variants," he added.

The virologist concluded that the current variant of the coronavirus "has changed, is changing, and will continue to change." However, he emphasized that the likelihood of more pathogenic variants is extremely low, as the immune segment of the population is constantly evolving and adapting to new strains.

Stratus, a member of the Omicron lineage, is more infectious than the early-epidemic strains, but less lethal. The mortality rate of the early Wuhan , Delta, and other strains is about 2%, while the mortality rate of the Omicron lineage is a fraction of a percent, Agranovsky explained. "Variants of the virus [like Stratus] gain an advantage and infect more people. The majority of such infections manifest as mild acute respiratory viral infections," he noted.

"Stratus" is primarily spreading in Southeast Asian countries but is gradually expanding beyond the region, Chumakov added. Although it has some differences from the previous JN.1 strain, there is currently no evidence of its increased danger compared to other circulating strains. The scientist reported that "the WHO classifies the risk as low."

The first case of the Stratus strain worldwide was detected on January 27, 2025, in CANADA. The first case in RUSSIA was registered on April 24.

Symptoms of the disease are generally mild and similar to other variants of Omicron. A characteristic symptom of Stratus is hoarseness.

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