Viruses: Variant, Mutant and Strain Differences

Ian C. Langtree - Writer/Editor for Disabled World (DW)
Published: 2021/04/14
Topic: Coronavirus Information - Publications List

Page Content: Synopsis - Introduction - Main

Synopsis: Article examines and describes the difference(s) between variants, mutants and strains when examining and discussing viruses. A mutant is the result of a mutation which is a change in the genetic material (DNA - RNA) and produces something new.

Introduction

Although the terms mutation, variant, and strain are often used interchangeably in describing the epidemiology of SARS-CoV-2, the distinctions are important. SARS-CoV-2 is a single strain of coronavirus and there are variants of that strain. The term strain is only appropriate when referring to Sars-Cov-2, the virus causing the Covid-19 disease - since it is a strain of the wider coronavirus family, including severe acute respiratory syndrome (SARS) and the Middle East respiratory syndrome (MERS).

Main Item

The distinction between a variant and a strain hinges on whether the virus in question behaves in a distinct way, according to Dr. Adam Lauring.

The genetic material of SARS-CoV-2 - the coronavirus that causes COVID-19 - is known as ribonucleic acid (RNA). To replicate and establish infection SARS-CoV-2 RNA must hijack a host cell and use the cell's own machinery to duplicate itself. Quite frequently errors will occur during the actual process of duplicating the viral RNA. The end result of this ends in the creation of viruses that though similar are not exact copies of the original virus. These errors in the viral RNA are known as mutations. Viruses with these mutations are called variants.

Strain

A strain is a genetic variant, a subtype or a culture within a biological species. Strains are often seen as inherently artificial concepts, characterized by a specific intent for genetic isolation. A strain of a virus has distinct properties and a particular immune response. SARS-CoV-2 is a single strain of a coronavirus - and there are variants of that strain.

Mutant

Mutation is the process by which a strain can take on new variants. Mutation refers to the actual change in sequence. A mutant is the result of a mutation which is a change in the genetic material (DNA - RNA) and produces something new. A mutation is simply the presence of a change in the nucleotide sequence of the RNA of the virus - that causes a change in an amino acid residue in a virally expressed protein.

Variant

Variant is the correct term to use when classifying a known virus that has developed a "specific group of mutations" that causes the variant to behave differently than that of the strain it originated from. A certain strain of virus is considered a variant when it has enough mutations to change a minor portion of its genetic code.

Genomes that differ in sequence are often called variants. This term is somewhat less precise because 2 variants can differ by 1 mutation or many. Strictly speaking, a variant is a strain when it has a demonstrably different phenotype (eg, a difference in antigenicity, transmissibility, or virulence). "Genomes that differ in sequence are often called variants," Lauring and Hodcroft explain in the Journal of the American Medical Association. "A variant is a strain when it has a demonstrably different phenotype." In addition, the authors of a recent article outlining the stain, mutant, variant differences in the journal JAMA also state that a variant becomes a strain when it has a "demonstrably different" phenotype, or characteristics.

Currently all known variants of COVID-19 belong to the SARS-CoV-2 strain and have not mutated enough to either be classified as their own strain or be ineffective against current and prospective COVID-19 vaccines.

Author Credentials: Ian was born and grew up in Australia. Since then, he has traveled and lived in numerous locations and currently resides in Montreal, Canada. Ian is the founder, a writer, and editor in chief for Disabled World. Ian believes in the Social Model of Disability, a belief developed by disabled people in the 1970s. The social model changes the focus away from people's impairments and towards removing barriers that disabled people face daily. To learn more about Ian's background, expertise, and achievements, check out his bio.