Rapid development of efficacious COVID-19 vaccines is one of the few true success stories from this pandemic. Vaccines remain so far effective against severe disease caused by all variants of concern, despite some drops in preventing mild forms of disease.

All viruses, including SARS-CoV-2, the virus that causes COVID-19, change over time. Although most changes have little to no impact on the virus’ properties, some may affect how easily it spreads, the associated disease severity, or the performance of vaccines, therapeutic medicines, diagnostic tools, or other public health and social measures.

Variants that pose an increased risk to global public health are defined by WHO as variants of interest (VOIs) or variants of concern (VOCs). A Variant of Interest can become a Variant of Concern if it proves to be a greater threat as demonstrated by international spread, greater disease severity, immune escape or ability to out-compete other strains. The classification of viruses enables the global community to prioritize monitoring and research, and ultimately to inform the ongoing response to the COVID-19 pandemic.

The following have been classified as variants of concern:

• The Alpha variant (B.1.1.7) is known to increase viral transmissibility and was previously the predominant variant in Europe. This variant has been described as having little escape from previous immunity.
• The Beta (B.1.351) variant is less easily neutralized by convalescent plasma obtained from patients infected with previous variants, and preliminary evidence suggests reduced efficacy of some vaccines against mild to moderate disease.
• The Gamma (P.1) variant can cause severe disease even in people who have been previously infected, although this information needs to be expanded with further studies. Similarly, moderate escape from the immune response has been described with this variant.
• The Delta (B.1.617.2) variant is more transmissible than previous variants and as of December 2021 is the dominant variant in the European Region.
• The Omicron (B.1.1.529) variant has a large number of mutations, some of which are concerning. It has been detected at faster rates than previous surges in infection, suggesting that this variant may have a transmission advantage. While characteristics of Omicron are being studied, evidence shows that COVID-19 vaccines are still effective to protect against severe disease due to current circulating SARS-CoV-2 variants, including Delta.

We must remain vigilant and not let down our guard down. While expanding vaccination and making vaccines available, especially to those at highest risk, we must continue public health and social measures, like wearing masks, frequently washing hands and physical distancing.