Omicron causes "a decrease in the effectiveness of the vaccine against infection" and, based on available data, "it is likely that Omicron will surpass the Delta strain" in infecting the community, according to a WHO report. The report said that Omicron cases to date have had only mild symptoms or almost no symptoms, but there is not enough data yet to make a comprehensive assessment of the virulence of this variant.
Three epidemiological teams in South Africa tracked the effects of Omicron and found that this variant causes milder symptoms than variants like Delta and Beta, but the rate of transmission of the latest variant in South Africa is "much faster" than that of the two others. 95% of the 20,000 new daily infections detected in South Africa involve the Omicron variant.