Delta Plus a 'variant of concern': How are Covid-19 variants categorised?

Categories are decided by taking into account how quickly a variant spreads, its ability to evade known medical intervention and its geographical reach

The Union Health Ministry has declared the Delta Plus variant of Covid-19 a “variant of concern” as the newest strain of the virus in the country raises alarm bells and necessitates closer surveillance.

The escalation in the variant’s classification comes a week after the Niti Aayog had said the new strain was only a “variant of interest” as not enough was known about its transmissibility and virulence.

Viral mutations are continually occurring in viruses, and a few of them make the virus much better at infecting people. These mutations are tracked by means of genome sequencing, surveillance, laboratory studies and epidemiological investigations, and grouped by health organisations under one of three categories — variant of interest, concern or high consequence.

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These categories are decided by taking into account how quickly a variant spreads in comparison to older strains, its ability to evade known medical intervention and its geographical reach.

Variant of interest

A variant of interest is defined as a strain that has been identified as having certain changes in its genetic makeup that have been known to change receptor binding, lower neutralisation by antibodies generated against earlier infection or vaccination, weaker efficacy of treatments, or predicted increase in transmissibility or severity of disease.

A variant of interest usually requires health bodies to monitor and sequence the strain, and investigate whether current methods of treatment hold against the new variant.

Currently, the Covid-19 variants Epsilon, Zeta, Eta, Theta, Iota, Kappa and Lambda fall into this category.

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Variant of concern

The difference between a variant of interest and a variant of concern is that there is evidence that the latter spreads faster, is more virulent or evades testing.

Variants of concern require health organisations to step up efforts to check their spread, ramp up testing and conduct research to determine how effective vaccines and treatments against the variant are.

The World Health Organisation (WHO) currently groups the Alpha, Beta, Delta and Gamma variants under this category.

Variant of high consequence

This categorisation has not been used yet, but exists as a possible category under guidelines drawn up by the WHO and the US Centres for Disease Control and Prevention.

A variant of high consequence will be categorised as such if it has shown clear evidence that existing prevention measures or measures have significantly diminished in effectiveness against the new variant.

There have been no known variants that fall under this category so far.