The World Health Organization (WHO) is updating the naming system for variants of SARS-CoV-2 — the virus that causes COVID-19 — to better reflect Omicron's global dominance and track its ongoing evolution.
Going forward, the organization's tracking system — a Greek alphabet-based approach to naming major variants of concern — will consider the classification of Omicron sublineages as either variants under monitoring, variants of interest or, in the case of the biggest potential threats, as variants of concern.
Since February 2022, "Omicron and its many sublineages have almost completely replaced other variants," Dr. Maria Van Kerkhove, an infectious disease epidemiologist who serves as the technical lead for WHO's COVID-19 response, noted in a series of social media posts.
The family of Omicron-related viruses now accounts for more than 98 per cent of the publicly available sequences, WHO said in a statement on Thursday, adding that the previous naming system didn't have the "granularity" needed to compare them.
The shift to a new system means several key changes:
WHO will continue assigning Greek alphabet labels for variants of concern, but it will no longer do so for variants of interest.
Variants such as Alpha, Beta, Gamma and Delta, as well as the Omicron parent lineage (B.1.1.529), are now considered previously circulating variants of concern.
Infectious diseases specialist Dr. Isaac Bogoch, who works at the University Health Network in Toronto, called WHO's move a "smart decision."
"We have been in the Omicron era for over a year, and the various sub-lineages have increasingly complex names that may be challenging for some in the general public to keep track of," he said in an email to CBC News, noting the complicated classifications of many of those offshoots, including BQ.1.1, CH.1.1, and XBB.1.5.
"Revisiting the definition of what a variant of concern is and naming these more appropriately may facilitate more effective communications between public health teams and the general public."
Bill Hanage, an epidemiologist with the Harvard T.H. Chan School of Public Health in Boston, said the shift also reflects that none of the lineages since the initial Omicron wave had remotely the impact of Alpha, Delta or the early Omicron strain, "with the important exception of China, which has only recently emerged from its first tussle with [Omicron]."
But overall, since then, the world has experienced SARS-CoV-2 offshoots that include relatively small changes that have "real but not huge" impacts on evasion of immunity, Hanage said, adding it doesn't make sense to call those variants of concern.
'Appropriate' to name XBB.1.5 a variant of interest
What WHO has done is deem Omicron subvariant XBB.1.5 — which appears to make up nearly half of all Canada's recent COVID-19 cases, still-accumulating federal data shows — as the new sole variant of interest, alongside multiple variants under monitoring.
That means it doesn't yet have a Greek-alphabet name, and it won't unless it is later declared a variant of concern.
The subvariant has been rising in more than 70 countries since it was first identified last fall and is thought to contain mutations giving it a major growth advantage.
"Fortunately, the variants that we've been seeing within Omicron, including the latest XBB.1.5, do not appear to be more severe, but their increased transmission means more cases, not just now, but into the future," said Sarah Otto, an expert in modelling and evolutionary biology with the University of British Columbia in Vancouver.
"Thus, elevating XBB.1.5 to [a variant of interest] is absolutely appropriate."
Scientists have been wondering whether Omicron would be the last named variant of concern despite its ongoing evolution, she said in an email exchange with CBC News, noting that WHO has been playing "catch-up" with this virus.
"This latest announcement indicates that WHO recognizes that variants of concern can beget even more concerning variants, as we've seen with the evolution of the various Omicron waves," she said.
WATCH | XBB.1.5 began rising in U.S. earlier this year:
WHO said it will continue to issue regular risk assessments for both variants of interest and those deemed to be of major concern.
The organization also stressed that the changes to its naming system don't imply that Omicron no longer poses a threat to public health.
"Rather, the changes have been made in order to better identify additional or new threats over and above those posed by the current Omicron viruses in circulation," the organization's statement reads.
Dr. Zain Chagla, an infectious diseases specialist at McMaster University in Hamilton, agreed that WHO's changes to factor in Omicron "make sense," since these tracking systems are really meant to alert health systems to anything novel that may "change the current pandemic dynamic."
But there's also always the possibility of an evolutionary curveball, according to Van Kerkhove, who wrote that "the emergence of a completely new variant outside of the Omicron family still remains possible."