Clinical lab scientist Selam Bihon processes upper respiratory samples from patients suspected of having COVID-19 at the Stanford Clinical Virology Laboratory on Wednesday, Feb. 3, 2021, in Palo Alto, Calif. Viruses mutate constantly. To stay ahead of the threat, scientists analyze samples for genetic changes, watching closely for ones that might make the virus more infectious or more deadly. (AP Photo/Noah Berger)
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