The first confirmed case of COVID-19 caused by the Omicron variant (B.1.1.529) has been identified in San Francisco, California. The individual had recently travelled to South Africa, where the variant was first reported to the World Health Organization.  According to the CDC, the individual had only mild symptoms and is improving.

First detected in Botswana and subsequently in South Africa, the Omicron variant has been shown to have a large number of mutations in portions of the genome that may make it more transmissible and possibly resistant to certain therapeutics. Classified as a Variant of Concern, Omicron has been detected in at least 20 countries worldwide.

Whether Omicron is more transmissible than other SARS-CoV-2 variants of concern (ie, Delta) is unknown; however, preliminary data suggest increased infectivity based on the mutations to the receptor binding protein of the variant virus.

The CDC is recommending that health care providers take a travel history for all suspected and confirmed cases of COVID-19. The local health department should be notified about the travel history if the case is confirmed and there is a history of international travel within 14 days before symptom onset, or if asymptomatic, a positive test.

Symptoms associated with COVID-19 infection from the Omicron variant appear to be similar to those seen with other variants. Individuals may also be asymptomatic. No unusual symptoms have thus far been reported. For people previously infected with SARS-CoV-2 or those who have been vaccinated, symptoms may be milder.

Vaccine manufacturers are working to test the available COVID-19 vaccines against Omicron. There is currently no data available on the effectiveness of monoclonal antibodies or antiviral therapies. In a statement, Regeneron, the developer of the monoclonal antibody therapy REGEN-COV® (casirivimab and imdevimab), noted that “prior in vitro analyses and structural modeling regarding the individual mutations present in the Omicron variant indicate that there may be reduced neutralization activity of both vaccine-induced and monoclonal antibody conveyed immunity, including the current REGEN-COV antibodies.”

At this time, the CDC recommends that health care providers closely follow the NIH COVID-19 treatment guidelines. In a briefing with President Biden, Chief Medical Advisor Dr Anthony Fauci reiterated the importance of vaccination as being the best means of protection against severe COVID-19 disease while additional data on Omicron is being gathered.


  1. First confirmed case of Omicron variant detected in the United States. The Centers for Disease Control and Prevention website. December 1, 2021.
  2. New SARS-CoV-2 variant of concern identified: Omicron (B.1.1.529) variant. The Centers for Disease Control and Prevention website. December 1, 2021.