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 Scientists are now tracking a rise in cases caused by a close cousin
known as BA.2, which is starting to outcompete BA.1 in parts of
Europe and Asia. The following is what we know so far about the new
subvariant:
"STEALTH" SUBVARIANT
Globally, BA.1 accounted for 98.8% of sequenced cases submitted to
the public virus tracking database GISAID as of Jan. 25. But several
countries are reporting recent increases in the subvariant known as
BA.2, according to the World Health Organization.
In addition to BA.1 and BA.2, the WHO lists two other subvariants
under the Omicron umbrella: BA.1.1.529 and BA.3. All are closely
related genetically, but each features mutations that could alter
how they behave.
Trevor Bedford, a computational virologist at Fred Hutchinson Cancer
Center who has been tracking the evolution of SARS-CoV-2, wrote on
Twitter on Friday that BA.2 represents roughly 82% of cases in
Denmark, 9% in the UK and 8% in the United States, based on his
analysis of sequencing data from the GISAID database and case counts
from the Our World in Data project at the University of Oxford.
The BA.1 version of Omicron has been somewhat easier to track than
prior variants. That is because BA.1 is missing one of three target
genes used in a common PCR test. Cases showing this pattern were
assumed by default to be caused by BA.1.
BA.2, sometimes known as a "stealth" subvariant, does not have the
same missing target gene. Instead, scientists are monitoring it the
same way they have prior variants, including Delta, by tracking the
number of virus genomes submitted to public databases such as GISAID.
As with other variants, an infection with BA.2 can be detected by
coronavirus home tests kits, though they cannot indicate which
variant is responsible, experts said.
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 MORE TRANSMISSIBLE?
Some early reports indicate that BA.2 may be
even more infectious than the already extremely
contagious BA.1, but there is no evidence so far
that it is more likely to evade vaccine
protection. Danish health
officials estimate that BA.2 may be 1.5 times more transmissible
than BA.1, based on preliminary data, though it likely does not
cause more severe disease.
In England, a preliminary analysis of contact tracing from Dec. 27,
2021, through Jan. 11, 2022, by the UK Health Security Agency (HSA)
suggests that household transmission is higher among contacts of
people infected with BA.2 (13.4%) compared with other Omicron cases
(10.3%). The HSA found no evidence of a difference
in vaccine effectiveness, according to the Jan. 28 report.
A critical question is whether people who were infected in the BA.1
wave will be protected from BA.2, said Dr. Egon Ozer, an infectious
disease expert at Northwestern University Feinberg School of
Medicine in Chicago.
That has been a concern in Denmark, where some places that saw high
case counts of BA.1 infections were reporting rising cases of BA.2,
Ozer said.
If prior BA.1 infection does not protect against BA.2, "this could
be sort of a two-humped camel kind of wave," Ozer said. "It's too
early to know if that will happen."
The good news, he said, is that vaccines and boosters still "keep
people out of the hospital and keep people from dying."
(Reporting by Julie Steenhuysen; Editing by Bill Berkrot)
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