New Delhi, May 3 Even after three years into the pandemic, SARS-CoV-2, the virus behind Covid-19, has not yet become seasonal. It will continue to cause mini-waves with mild infections, scientists contended in an article in the science journal Nature.
Scientists have long predicted that Covid pandemic will end up into a seasonal pattern of spread, like influenza has. However, a series of mini waves fueled by newer variants like XBB.1.16 are "different from the slower, annual circulation patterns of influenza and cold-causing coronaviruses".
"It seems increasingly unlikely that SARS-CoV-2 will settle into a flu-like rhythm anytime soon," the scientists said in Nature.
"We haven't slowed down in the last year, and I don't see what factors would cause it do so at this point," Trevor Bedford, an evolutionary biologist at the Fred Hutchinson Cancer Center in Seattle, Washington, was quoted as saying.
"It will be a continually circulating respiratory disease. It may be less seasonal than things we're used to," he added.
Bedford noted that some countries are seeing fresh surges in Covid about "three or four times each year, driven largely by the breakneck pace at which the virus continues to change".
"Currently, SARS-CoV-2's spike protein, in which most immunity-evading mutations occur, is evolving at twice the rate of a similar protein in seasonal influenza and about 10 times as quickly as those of cold-causing 'seasonal' coronaviruses".
This is seen as in the case of India, where XBB.1.16 displaced other variants to become the dominant one. While it spread rather quickly than previous variants, leading to a surge in cases it caused only mild infections.
"We see that it has almost replaced all other variants in India, and we think the same thing will be followed everywhere," Rajesh Karyakarte, a microbiologist at Byramjee Jeejeebhoy Government Medical College in Pune, was quoted as saying.
Similarly in the UK, there's a 100 per cent annual 'attack rate', Bedford said. In the future, "we can still imagine 50 per cent attack rates every year, half the population getting infected", compared with around 20 per cent with influenza.
According to Tom Wenseleers, an evolutionary biologist at the Catholic University of Leuven in Belgium, the combination of rapid mutation and short-lived human immunity is probably preventing Covid from settling into seasonal patterns of circulation.
Although the World Health Organization (WHO) declared XBB.1.16 a 'variant of interest', whether it or another new variant will cause a spike in infections in a particular country will probably depend on the size and timing of the country's earlier waves, he added.
Yet, the increased infection waves are only mild causing smaller ripples in hospitalisations and deaths. In a study, posted to a medRxiv.org preprint server, and not yet peer reviewed, Karyakarte and his team analysed more than 300 cases, from last December to early this month.
They found that XBB.1.16 infections tend to cause mild symptoms similar to those from earlier Omicron variants, with few hospitalizations and deaths. "We didn't see much," Karyakarte said.
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