A brief account on SARS-CoV-2 variants

Information retrieved from World Health Organization website on 15 December 2021.

The World Health Organization (WHO) monitors and coordinates the efforts of member states in the fight against SARS-CoV-2 coronavirus, which is responsible for the COVID-19 pandemic. Viruses mutate rapidly, meaning that many different strains (variants) of virus can circulate in parallel, each with potentially different rate of transmission, severity and nature of disease caused, and resistance to current treatments and preventive measures (hereon referred to as Traits).

Naming and Classification

The scientific community labels each strain of virus using different systems based on the compiling of genetic analysis results. However, these labels are difficult to use by media and the non-expert population. WHO has adopted through their Technical Advisory Group on Virus Evolution (TAG-VE) simple-to-use and non-discriminatory Greek letter labels for key variants.

WHO distinguishes three categories of relevant variants (in decreasing order of health risk): VOC, VOI, and VUM, the former two accounting for key variants. The following descriptions are based on WHO working definitions:

  • VOI Variant of Interest presents genetic changes known or predicted to affect Traits and is observed to cause an increase in total number of cases with increasing strain prevalence.
  • VOC Variant of Concern fulfils the criteria for VOI and additionally is shown to cause a detrimental change to any one of the Traits on a scale significant to global health.
  • VUM Variant under Monitoring has genetic changes suspected to impact virus characteristics and some indication for possible future risk.

Variants that are no longer circulating, have been circulating without an impact for a long time, or have been classified of no concern using scientific data stop being monitored.


The actions required of member states and the WHO to manage the pandemic in the context of rapid virus evolution are as follows:

  • Member State reports detection of a new strain and its possible classification to WHO and uploads genetic sequencing data to a public database, such as GISAID. If resources allow, conducts further laboratory and field research to assess impact genetic changes have on Traits.
  • WHO gathers and analyses data to monitor on a global level spread of novel strain and the impact it has on public health, in comparison to other strains. When required, coordinates research efforts between member states. If a strain has been labelled as VOC, WHO reports on the findings to member states and updates guidance, if necessary.

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