The difference between variants, strains and mutations

Different types of viruses have been labelled as variants, mutations and strains, which has confused many people as these terms also apply to the Covid disease. While we may all understand terms like PPE, contact tracing and social distancing, these terms may need a little extra explanation on what they mean and how they differ from each other.

Coronavirus is caused by a single species, the SARS-CoV-2 virus, but there are kinds of Coronavirus that cause basically the same disease. Coronavirus refers to the species or virus particle, Covid refers to the disease and Covid-19 refers to the pandemic or the disease.

So what is the correct way to refer to a certain kind of Coronavirus?

A strain is categorized by its genetic characteristics, but can differ from species to species on which features are important. It has demonstrably different phenotype or characteristics, shows distinct physical properties and is built and behaves differently from its parent virus. These differences can be subtle or obvious. The strain will also have a particular immune response. The term strain is specific to the virus SARS-CoV-2, but not COVID-19, the disease caused by it.

According to science, a mutant is the result of a mutation, which is a change in the genetic material of DNA or RNA and creates something new. This results in viruses that are similar, but not exact copies of the original virus. The mutation may have never appeared in the past, or it could reappear in the population, which means it is a genetic variant that is either new or has only occurred rarely. A mutant has mutated comparably to another type that is considered common or ‘wild type’. Therefore, mutants are either recent or rare. Not all mutations have the same effect, when a mutation occurs at a single point in the DNA or RNA, it won’t necessarily change any of the building blocks and won’t change how the organism is built. Occasionally, these mutations occur in part of the DNA or RNA that causes a change in a building block and there could be many mutations that alter the building block. Viruses often mutate, but some do it more than others.

Viruses with mutations are called variants. Variants could differ by a single or many mutations. A certain strain of virus is considered a variant when it has enough mutations to change a portion of its genetic code. One of the major mutations seen in variants is that of the spike protein, which has improved how it invades human cells. If the variant displays different physical properties to the original virus, it is called a strain. All strains are variants, but not all variants are strains. This makes sense then, why variant has been the most widely-used term to describe the new types of Coronavirus. Health officials don’t need to recognize every variant of the virus, but they do need to determine which are important and which ones may change who becomes infected with the virus, the symptoms or how it responds to vaccines.

When deciding which is the correct word to use, remember that ‘mutant’ and ‘strain’ can only be used for organisms and not outcomes. Therefore, if you said “Covid mutant” or “Covid-19 strain” it would be grammatically incorrect. As you would basically be saying “disease mutant” or “pandemic strain”, which just don’t make sense. Accordingly, ‘Covid variant’ would be the correct choice, as it can be applied to both the virus and disease without being incorrect. Variant is correct 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.

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