Omnicron

Omnicron, often referred to as the Omicron variant, is a variant of the virus that causes COVID-19, SARS-CoV-2. It was first reported to the World Health Organization (WHO) from South Africa on November 24, 2021. The WHO designated it as a Variant of Concern on November 26, 2021, naming it Omicron, the 15th letter of the Greek alphabet. This designation was due to its significant number of mutations, particularly in the spike protein, which raised concerns about its transmissibility, immune evasion, and potential for increased severity.

The Omicron variant quickly became the dominant strain of SARS-CoV-2 globally, outcompeting previous variants. Studies indicated that it was significantly more transmissible than earlier strains, leading to rapid surges in infection rates worldwide. While initial concerns about increased severity were debated, evidence generally suggested that Omicron infections, on average, led to less severe disease compared to the Delta variant, especially in vaccinated individuals. However, due to its high transmissibility, it could still cause significant strain on healthcare systems.

Vaccines and previous infections provided some protection against Omicron, but the variant showed a notable ability to evade antibodies generated by prior vaccination or infection. This led to a rise in breakthrough infections and reinfections. Booster doses of vaccines were found to significantly increase antibody levels and restore a higher degree of protection against symptomatic infection and severe outcomes from Omicron.

Sub-lineages of Omicron, such as BA.1, BA.2, BA.4, and BA.5, emerged and became dominant at different times, each with slightly different characteristics in terms of transmissibility and immune escape. These subsequent Omicron subvariants continued to circulate and evolve, contributing to ongoing waves of COVID-19.