SARS-CoV-2 Variants, Explained | Prognosis: Covid UNCUT

Viruses mutate all the time, including the one, SARS-CoV-2, that’s caused

the Covid-19 pandemic. Although most genetic changes are innocuous,

some can make the mutant more adept at infecting cells, for example, or

evading antibodies. Such “fitter” variants can outcompete other strains, so

that they become the predominant source of infections. A succession of

more-transmissible variants has emerged over the past year, each harboring

a constellation of mutations. The most worrisome so far is the so-called delta

variant. It’s become dominant in much of the world since its discovery in

India in October 2020, leading to surges in cases and hospitalizations,

especially in places where less than half the adult population has been fully

immunized.

What’s a variant?

During replication, a virus often undergoes genetic changes that may create

what are called variants. Some mutations weaken the virus; others may yield

an advantage that enables it to proliferate. If changes produce a version with

distinctly different physical characteristics, the variant may be co-termed a

strain. A variant that deviates significantly from its viral ancestors may be

identified as a new lineage, or branch on the evolutionary tree. In general

discourse, however, the terms are often used interchangeably.

What are the most worrisome ones?

The World Health Organization uses “variants of concern” to signify strains

that pose additional risks to global public health, “variants of interest” for

those that warrant close monitoring because of their emerging risk, and

“alerts for further monitoring” for a variant that possesses genetic

characteristics that indicate it may pose a future risk. As of Oct. 10, the

World Health Organization had four variants of concern and two variants of

interest:

Alpha

This variant emerged in England in September 2020 and drove a surge in

cases that sent the U.K. back into lockdown in January. Other countries,

particularly in Europe, followed the U.K. in reimposing movement

restrictions. Alpha was previously the dominant strain in the U.S., and has

been reported in at least 195 countries, according to the WHO.

Beta

This one, which appeared in South Africa in August 2020, led to a

resurgence in Covid cases that overwhelmed southern Africa. It’s been

reported in at least 145 countries.

Gamma

This variant, first spotted in the Amazon city of Manaus in December 2020,

has contributed to a surge in cases that strained Brazil’s health system and

led to oxygen shortages. A study there found gamma was associated with a

higher incidence and an increased proportion of severe Covid cases among

20-to-30-year-olds, as well as among women generally. It also found the

proportion of deaths was higher among people of both sexes between 20

and 59. The variant has been found in at least 99 countries.

Delta

This fast-spreading variant has since been found in at least 191 countries

since helping to drive a large wave of Covid cases in India. It’s estimated to

be 55% more transmissible than alpha and almost twice as infectious as the

original strain from early 2020. That may be because those infected with the

variant can have significantly more infectious viral particles in their airways

compared with individuals with other strains. Those particles appear to bind

more efficiently with ACE2, the enzyme on the surface of cells that the virus

targets to start an infection.

New delta variants have been reported in several countries including India,

the U.K. and Vietnam. A strain that includes the K417N mutation - dubbed

“delta plus” in India - has stoked some concern, since that genetic change is

also harbored by the beta strain that’s associated with an increased risk of

reinfection. Researchers in Germany said in October that delta plus doesn’t

appear to be significantly more dangerous than delta.

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