Vaccine efficacy and duration of protection

Why has Omicron been designated a variant of concern, and can it affect people who are already vaccinated?


WHO designated the variant B.1.1.529 (named Omicron) a variant of concern on 26 November 2021. It has a large number of mutations, some of which are concerning, because they can potentially affect virus characteristics such as transmissibility, disease severity, immune escape, diagnostic or therapeutic escape.

Omicron has been shown to be more transmissible and less severe compared to the Delta variant, especially in those vaccinated. However, it should not be categorized as mild. Vaccines are highly effective in protecting against severe COVID-19 disease and death, including Omicron variant, but they do not eliminate the risk of infection and their effectiveness against symptomatic disease for Omicron variant appears to be reduced. As a result, more vaccinated people are likely to develop a breakthrough infection due to Omicron. However, these studies also show that vaccination continues to provide a high level of protection against severe disease and hospitalization linked to the Omicron variant.

Vaccines will continue to be the most important first line of defense against this disease, and they are especially important for people who are most at risk, including older adults, health workers and people with underlying health conditions.

The best way to prevent infection and serious disease caused by Omicron or any other SARS-COV-2 variant is by getting vaccinated and remembering to also maintain physical distance, wear a mask when distancing is not possible, frequently wash hands and ventilate indoor spaces.