As the flu season begins, global health authorities are increasingly concerned about a new influenza strain that emerged in June—four months after this year’s vaccine formulations were finalized. The strain, a variant of H3N2, is driving outbreaks in Canada and the United Kingdom, prompting warnings from public health officials about an early and potentially severe flu season.
“Since it emerged, it’s rapidly spreading and predominating in some countries in the Northern Hemisphere,” said Dr. Wenqing Zhang, head of the World Health Organization’s Global Respiratory Threats Unit, during a recent media briefing.
H3N2 Variant Shows Significant Mutations
The current H3N2 variant circulating globally has acquired seven new mutations over the summer, according to Antonia Ho, a consultant in infectious diseases at the University of Glasgow. “This means the virus is quite different from the H3N2 strain included in this year’s vaccine,” Ho noted.
In the U.K., officials are bracing for a severe winter. James Mackey, head of the National Health Service, reported that flu cases are already triple the numbers seen at this time last year. Similar trends are emerging in Canada, where virologist Angela Rasmussen of the University of Saskatchewan emphasized that H3N2 generally causes more severe illness, particularly among older adults.
Japan is also experiencing an unusually early and intense flu season. Nippon TV reported that as of November 4, flu cases in Tokyo had surged nearly sixfold compared to the same period last year. Over 2,300 schools and day care centers have been partially closed due to the outbreak. “These are not good signs,” Rasmussen said.
U.S. Preparedness Remains Unclear
Although anecdotal reports suggest that flu A is present in the U.S., there is limited nationwide data. The Centers for Disease Control and Prevention (CDC) has not issued a detailed report on flu activity since September 26, due to a government shutdown.
Dr. William Schaffner, an infectious disease expert at Vanderbilt University Medical Center, cautioned that staffing cuts at the CDC could further delay data collection and analysis. “We will be dependent on state and academic laboratories for reporting,” Schaffner said. “The information will not be as comprehensive, centralized, or rapidly communicated as in previous years.”
Vaccine Effectiveness and Recommendations
Flu vaccines for the Northern Hemisphere are selected each February based on circulating strains in the Southern Hemisphere. This year’s vaccine protects against three influenza strains, including two A strains and one B strain.
While the flu shot does not completely prevent infection, it reduces illness severity and the risk of hospitalization. Last year, the vaccine prevented up to 55% of adult hospitalizations due to flu. Preliminary data from the U.K. suggest this year’s vaccine is up to 40% effective in preventing hospitalizations among adults.
Despite the mismatch between the vaccine and the new H3N2 variant, Schaffner strongly encourages vaccination. “Even if there is not a perfect match, the vaccine continues to prevent hospitalizations and ICU admissions and helps save lives,” he said.
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