The vanishing flu strain: Why Canada’s seasonal vaccine is changing

A strain of seasonal influenza has wholly vanished globally since March 2020, and owed to its disappearance, wellness officials successful Canada are changing up nan yearly flu vaccine.

The B/Yamagata influenza strain, erstwhile a ascendant unit among influenza B viruses, whitethorn person vanished wholly owed to nan stringent measures imposed during nan COVID-19 pandemic, according to nan National Advisory Committee connected Immunization (NACI). No cases person been confirmed crossed nan globe since March 2020.

Due to nan strain’s disappearance, NACI announced connected July 26 that master groups person endorsed removing nan B/Yamagata constituent from influenza vaccine formulations. As a result, Canada’s flu vaccine will displacement from a quadrivalent to a trivalent formula.

“As of March 2020, pursuing nan onset of nan COVID-19 pandemic and implementation of measures to trim nan transmission of SARS-CoV-2, location person been nary confirmed detections of people circulating B/Yamagata lineage viruses worldwide, including successful Canada,” NACI said successful nan statement.

“Based connected existent epidemiological data, location is world master statement that B/Yamagata microorganism strains should beryllium removed from influenza vaccine formulations and that manufacturing should modulation to trivalent vaccines exclusively,” it added.

Before nan strains disappeared, location were 4 strains of seasonal influenza circulating: 2 from influenza A (H1N1 and H3N2) and 2 from influenza B (B/Victoria and B/Yamagata).

Since nan 2014 to 2015 flu season, Canada has utilized quadrivalent influenza vaccines containing strains from some influenza B lineages (B/Victoria and B/Yamagata) to connection protection against circulating influenza B viruses.

Although influenza A is usually nan ascendant strain, some influenza A and B lend to seasonal epidemics. Despite its little wide prevalence, influenza B tin still airs a important load successful Canada, accounting for up to 44 per cent of reported laboratory detections successful immoderate seasons, according to NACI.

“In November, December and into January, we mostly spot influenza A. And past successful nan second portion of nan season, January, February and tailing disconnected done March, we’ll spot a small spot much influenza B,” explained infectious diseases master Dr. Isaac Bogoch.

“If you look astatine nan absolute number of cases, we usually person measurement much influenza A compared to influenza B, but B starts to show up a small spot later connected successful nan season.”

He said that while nan diagnosis, prevention, and curen of influenza A and B are nan same, what differs is their epidemiology. This quality successful epidemiology mightiness explicate why B/Yamagata vanished while different strains persisted.

The B/Yamagata strain was first discovered successful Japan successful nan precocious 1980s. It began spreading globally and became a predominant influenza strain successful North America by nan early 2000s.

By nan 2014 to 2015 flu season, Canada had added the B/Yamagata strain to its seasonal flu vaccine, making it a quadrivalent look to protect against much influenza types.

In Canada and globally, betwixt 2012 and 2017, B/Yamagata viruses caused a larger proportionality of influenza B infections than B/Victoria, NACI said. However, 2 years earlier nan COVID-19 pandemic, nan B/Yamagata lineage started becoming dominant.

Then, successful March 2020, it seemingly vanished.

“During nan darkest days of COVID, we stopped detecting 1 of nan 2 influenza B strains and that was B/Yamagata,” Bogoch said. “Was it hiding retired location aliases was it conscionable circulating successful little levels? Was it going to someway look later on? Those are questions that were asked astatine that time. But, it didn’t look to travel back.”

Although it has disappeared, Bogoch emphasized that this does not mean nan strain is eradicated, arsenic eliminating immoderate microorganism is highly challenging.

But location are theories astir what happened to it.

The first mentation relates to nan nationalist wellness measures implemented astatine nan commencement of nan pandemic.

A 2022 study published successful Nature, based on that since April 2020, galore countries person seen historically debased seasonal influenza microorganism circulation, attributable to quarantines, societal distancing, schoolhouse and workplace closures, mask-wearing, aboveground disinfection and enhanced manus hygiene.

Bogoch suggested that different facet contributing to nan B/Yamagata strain’s disappearance could beryllium nan “massive driblet successful quality mobility” during nan pandemic.

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“If you look astatine world travel, rider volumes and quality mobility patterns during that time, they were a mini fraction of what they are normally” he explained.

“And erstwhile you look astatine really seasonal influenza is transmitted, it goes from nan confederate hemisphere and past it useful up its measurement into nan bluish hemisphere during our wintertime months, and past backmost to nan confederate hemisphere during their wintertime months and ping-pongs backmost and forth.”

He believes that nan adjacent standstill successful recreation during nan pandemic, on pinch tighter separator restrictions, whitethorn person contributed to nan diminution of nan strain.

Another logic could beryllium “viral interference,” he said, meaning nan COVID-19 strain whitethorn person helped suppress a weaker strain of influenza.

However, he stressed that these are each theories, and a operation of these factors whitethorn person contributed to nan disappearance of nan B/Yamagata strain.

These are conscionable nan early stages of transitioning from a quadrivalent to a trivalent seasonal influenza vaccine, truthful nan caller look will not beryllium disposable for nan 2024 to 2025 flu season, according to NACI.

“For nan 2024-2025 influenza play successful Canada, vaccine readiness is anticipated to stay unchanged. Quadrivalent formulations will proceed to beryllium supplied for nationalist programs. No trivalent formulations will beryllium disposable for modular dose aliases precocious dose inactivated influenza vaccines,” it stated.

NACI anticipates a gradual modulation to trivalent influenza vaccines, acknowledging important logistical challenges and imaginable regulatory complexities. More specifications astir trivalent influenza vaccines will beryllium included successful nan 2025 to 2026 Influenza Seasonal Statement.

Both quadrivalent and trivalent influenza vaccine formulations are clinically safe and effective, according to NACI.

While nan updated vaccine whitethorn not beryllium disposable successful Canada this upcoming flu season, nan U.S. has already adopted nan trivalent formulation for nan 2024 to 2025 season.

The Centers for Disease Control and Prevention (CDC) has announced that flu vaccines will beryllium trivalent successful nan United States for nan 2024-2025 season.

“Because influenza B/Yamagata lineage viruses person not been detected aft March 2020, nan World Health Organization (WHO) and FDA’s Vaccines and Related Biological Products Advisory Committee (VRBPAC) recommended that nan influenza B/Yamagata lineage vaccine microorganism constituent beryllium excluded from flu vaccines arsenic soon arsenic possible,” nan CDC website states.

Since there’s nary grounds that B/Yamagata is wholly eradicated, NACI said it will proceed to show each flu season.

“Continued epidemiological and virological monitoring of influenza virus, investigation of immoderate reports of B/Yamagata detection, and continued appraisal of programmatic factors remains important, arsenic does clear and transparent connection of updated recommendations,” it said.