What you should know about Omicron subvariants EG.5 and BA.2.86

Just as they have every autumn since 2020, COVID-19 infection and hospitalization numbers have begun to rise across Canada as summer winds down into September.

In a televised technical briefing on Tuesday, Canada's Chief Public Health Officer Dr. Theresa Tam assigned some of the blame for this uptick in COVID-19 activity to new Omicron subvariants.

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"The Omicron variant continues to evolve," Tam said, "with XBB subvariants such as EG.5 continuing to circulate in Canada and globally."

On Tuesday, Health Canada approved a new COVID-19 vaccine formulation from Moderna that targets the Omicron subvariant XBB.1.5. That strain was first detected in the United States in October 2022, where it quickly overtook other circulating strains.

It was first detected in Canada in November 2022 and has since given rise to EG.5.

EG.5 and another new subvariant, BA.2.86, have recently become a key part of conversations about how this fall's anticipated spike in COVID-19 cases will play out.

Here is what we know about the latest Omicron subvariants.

THE BASICS

EG.5 is a subvariant of XBB.1.5 that was first detected in February, according to the World Health Organization.

It is now estimated by Health Canada to be the dominant strain here, accounting for an estimated 34 per cent of sequenced COVID-19 infections as of the week of Sept. 3. Health Canada uses predictive modelling to estimate the current situation based on earlier trends and later updates the numbers with actual data from the National Genomic Database.

The BA.2.86 Omicron subvariant was first detected in Denmark and Israel in mid-August, and had appeared in the United States by Aug. 23, according to the Centers for Disease Control and Prevention.

According to Tam, Canada has detected 11 cases of BA.2.86 as of Sept. 12.

TRANSMISSIBILITY, SYMPTOMS AND SEVERITY

In its initial risk evaluation of EG.5 on Aug. 9, the World Health Organization said the strain presents a low overall level of risk, with moderate transmissibility, moderate vaccine resistance and low symptom severity.

Tam made the same assessment during the technical briefing on Tuesday.

"So far, none of the recent subvariants of Omicron have demonstrated increased virulence or severity," she said.

Because BA.2.86 hasn't been circulating for as long, there isn't as much data available to give clues as to its severity and transmissibility, however, Tam said there is some data coming out of the United Kingdom that appears promising.

"According to some laboratory data… BA.2.86 subvariant appears to be less able to infect cells," she said. "So that gives us a little bit of a clue, which is also good news, but we have to monitor that quite closely as well."

She said there is no evidence so far that either subvariant results in "any different range of symptoms or increased severity."

The most common symptoms of these subvariants, as with other strains of COVID-19, include runny nose, sneezing, sore throat and headache. Other, less common symptoms can include persistent cough, joint pain, chills, fever, dizziness, muscle pain, gastrointestinal symptoms and new loss, or altered sense, of smell.

VACCINES

In its Aug. 9 risk evaluation report for EG.5, the WHO said laboratory tests showed the variant could be somewhat vaccine resistant, with the ability to "escape or decrease" the effects of antibodies in COVID-19 vaccines.

However, while offering details about Moderna's Spikevax XBB.1.5 vaccine on Tuesday, Tam said the updated vaccine is expected to work as well with the two subvariants as it does with XBB.1.5.

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"Preliminary clinical data have shown promising immune responses from the Omicron XBB.1.5, the vaccine receiving regulatory authorization today, against various Omicron sublineages, including EG.5 and BA.2.86," Tam said. "This improved immune response is expected to better protect against the strains that are circulating in our communities."

Therefore, she said, anyone who has not been infected with COVID-19 or received a COVID-19 vaccination in the past six months should get vaccinated with the most up-to-date version of a COVID-19 vaccine as soon as they can.

Meanwhile, Health Canada is also reviewing submissions from Pfizer-BioNTech and Novavax seeking authorization for their respective XBB.1.5 COVID-19 vaccines.

OUTLOOK

While the clinical data is promising, Health Canada's Chief Medical Advisor Dr. Supriya Sharma said time will tell how the variants actually behave as they continue to spread throughout this fall.

"We're still in the process of looking at that data and getting that data in, and if there are any concerns, obviously we will communicate that." Sharma said during the technical briefing on Tuesday.

Although health officials are always concerned about the potential strain each seasonal wave of SARS-CoV-2 infections will impose on already vulnerable health-care systems across the country, she said there is some cause for relief.

"The concern really around some of the new variants was primarily around BA.2.86, because it was so highly mutated," she said. "I wouldn't say it's a nothingburger, but it doesn't seem like it's the one that would dominate at this point in time."