Bracing for the Omicron tsunami

Current data indicates that Omicron can escape some of the protective effect of Covid-19 vaccines, although it causes less severe disease in those who are vaccinated. — AFP

As viruses spread in the population, it is normal for them to change (or mutate) with time.

When the changes (or mutations) cause the changed (or mutated) virus to become significantly different from the original one, they are termed variants.