A new variant of Omicron is sweeping across the US this winter season — but experts insist it's not more likely to cause severe illness or death. - another spinoff of - is behind roughly 70 percent of new infections in the worst affected parts of the US and four in 10 nationally.It has spread rapidly in recent weeks, accounting for just four percent of US cases in early December, indicating it has a major growth advantage over rival strains.
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