The heavily mutated omicron variant of SARS-CoV-2, the virus that causes COVID-19, was first detected in late 2021.
Due to the many mutations in the spike protein (a protein on the surface of SARS-CoV-2 that allows the virus to attach to our cells) omicron was able to quickly become the dominant SARS-CoV-2 variant. These mutations allowed it to bind to respiratory cells more tightly than previous variants, rendering it more infectious.
