Why the term 'strain' might be misleading your understanding of COVID-19

Science · Published 9 October 2026 Swipe more like this →

In short: When we hear about new versions of a virus, we often use the word 'strain.' But in the world of virology, that term can be imprecise. Scientists are currently distinguishing between simple mutations and the emergence of distinct, high-impact variants that actually change the course of a pandemic.

The distinction between a mutation and a 'strain' is a matter of scale and impact. While viruses constantly undergo genetic changes as they replicate, these minor tweaks do not always result in a new version of the virus that behaves differently in the population. Scientists monitor these changes closely to determine if a mutation has evolved into a distinct variant with properties that significantly alter how the virus spreads or affects human health. Researchers are currently tracking these mutations to see if the virus develops into different strains. This ongoing observation helps determine if the virus is truly evolving into a new form. They watch for these changes to see if they develop into distinct versions.

To manage this complexity, organizations like the European Centre for Disease Prevention and Control (ECDC) use a specific classification system. Rather than just labeling everything as a new strain, they categorize variants based on their level of risk. These categories include variants under monitoring, variants of interest, and variants of concern. This tiered approach allows health officials to communicate which specific genetic lineages require urgent public health action and which are simply being tracked for data. Such evaluations are managed by the ECDC's multidisciplinary SAVE Working Group. This multidisciplinary team meets every month to review the impact of new variants. They provide updates through the European Respiratory Virus Surveillance Summary.

The process is highly technical, involving multidisciplinary teams that analyze genomic horizon scanning and epidemic intelligence. They look for specific changes, such as mutations in the spike protein, and map these against Pango lineages—a standardized nomenclature for tracking the virus's family tree. By focusing on these specific markers, researchers can differentiate between a virus that is merely changing its 'accent' and one that is fundamentally altering its biological behavior. The WHO proposed specific labels for global variants of concern and interest starting in May 2021. These labels are used alongside scientific names to help the public understand the data. Detailed tables also list the specific countries where these lineages were first detected.

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