It is not yet clear whether infection with Omicron causes more severe disease compared to infections with other variants, including Delta. Preliminary data suggests that there are increasing rates of hospitalization in South Africa, but this may be due to increasing overall numbers of people becoming infected, rather than a result of specific infection with Omicron. There is currently no information to suggest that symptoms associated with Omicron are different from those from other variants.

Thirty-two mutations affect the spike protein, the main antigenic target of antibodies generated by infections and of many vaccines widely administered. Many of those mutations had not been observed in other strains

On 26 November, BioNTech said it would know in two weeks whether the current vaccine is effective against the variant and that an updated vaccine can be shipped in 100 days if necessary. AstraZeneca, Moderna and Johnson & Johnson were also studying the variant's impact on the effectiveness of their vaccines

Worry about the potential economic impact of the Omicron variant led to a drop in global markets on 26 November, including the worst drop of the Dow Jones Industrial Average in 2021, led by travel-related stocks. The price of Brent Crude and West Texas Intermediate oil fell 10% and 11.7%, respectively.[81] Cryptocurrency markets were also routed.[82][83] The South African rand has also hit an all-time low for 2021, trading at over 16 rand to the dollar, losing 6% of its value in November.[84][85][86] As of 28 November 2021, all known cases outside of South Africa and Botswana have been travel related. The Belgium case was related to Egypt. Recent travelers have been subject to more testing, biasing the results