COVID-19 mutant. According to the query of Guangming. com. Delta is a mutant of COVID-19, which was first discovered in Indian in June, 2020. Delta mutant was listed as a worrying COVID-19 mutant by the World Health Organization, and its transmission ability was significantly enhanced compared with the previous strains. The proportion of patients infected with Delta strain with early fever symptoms is low, and most patients only show fatigue, olfactory disturbance, mild muscle soreness, abdominal distension, abdominal pain and lethargy.