How effective are the current SARS-CoV-2 vaccines against the Omicron variant?

The Omicron variant (B.1.1.529) was classified as a variant of concern by WHO on 26 November 2021 (WHO 2021). The variant first emerged in South Africa where the current vaccination rate among adults is approximately 24% and was associated with a rapid increase in infection rates. The variant is now present in more than 60 countries around the world. How quickly this variant will become dominant and the rate of community spread in populations with higher vaccination rates remains unclear. The situation is changing rapidly and it is anticipated that the Omicron variant will become the dominant variant globally within weeks.

The significance of the mutations in the Omicron variant remains under investigation. Mutations in the SARS-CoV-2 viral genome, especially those regions encoding the surface spike protein and the receptor binding domain, have been associated with increased transmissibility and higher rates of symptomatic COVID-19 illness (Davis et al 2021; Mlcochova et al 2021; Nasreen et al 2021). Such mutations also have the potential to reduce the effectiveness of vaccines against SARS-CoV-2 if they alter critical binding sites on the viral surface. Current vaccines are expected to provide protection against severe illness, hospitalizations and death due to the Omicron variant. Protection against infection is anticipated to be less robust (CDC 2021). Preliminary data suggest that the variant may be several times more transmissible than the Delta variant, even among individuals who have received a full vaccine dose, although a booster (third) dose of an mRNA vaccine appears to be associated with an increased level of protection from infection (Cele et al 2021; Pfizer Press Release December 8, 2021). For this reason, many countries are now increasing the rate and shortening the interval for booster vaccination.