WHO orders complete overhaul of flu shots for 2024-2025 to target a new, aggressive H3N2 subclade K strain, with vaccines showing 37% effectiveness against it.
Complete replacement of all three viral strains has been recommended for the Northern Hemisphere’s upcoming influenza season. The World Health Organization announced that vaccine manufacturers should update every strain included in next season’s flu shots. (1✔ ✔Trusted Source
WHO updates all 3 viral strains to be included in fall flu shots
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As anticipated, vaccines for the next flu season will include a newly emerging influenza variant that began rising last fall, too late to be incorporated into this winter’s formulations.
With current production methods, manufacturers require at least six months of preparation to produce flu shots in time for immunization campaigns that begin in late summer or early fall.
Emergence of Influenza A H3N2 Subclade K
The new variant, known as influenza A(H3N2) subclade K, was first reported in October after seasonal vaccines had already been produced and distributed to pharmacies and clinics.
As a result, a mismatch occurred between the strains included in vaccines and those circulating widely, explained Danuta Skowronski MD, a flu specialist at the British Columbia Centre for Disease Control in western Canada.
Although vaccines prepared for the Southern Hemisphere were slightly updated compared with those used in the United States this year, subclade K surfaced too recently to be included for the upcoming season in countries such as Australia and South Africa. In the Southern Hemisphere, flu activity generally runs from April through October, peaking between June and September.
Additional Influenza A and B Strain Updates
Beyond subclade K, two other strains were also recommended for modification in fall flu shots. The updated composition includes two influenza A viruses and one influenza B virus.
Concerns had emerged among scientists and public health authorities that existing flu shots in the Northern Hemisphere might offer little protection against subclade K, which appears to spread more easily and potentially cause more severe illness than other strains.
Vaccine Effectiveness Against Circulating Viruses
However, effectiveness exceeded expectations. An interim report released earlier this month showed that the latest flu vaccines in Canada lowered the risk of illness caused by influenza A(H3N2) viruses, severe enough to require an outpatient medical visit, by 40 percent compared with unvaccinated individuals.
Protection against subclade K reached 37 percent for medically attended infections, while effectiveness against the H1N1 influenza A strain was 31 percent.
These results were only slightly lower than effectiveness observed in previous years for H3N2 viruses, suggesting that current vaccines still provided meaningful protection.
Global Collaboration After United States Withdrawal
These recommendations marked the first influenza guidance issued since the United States withdrew from the World Health Organization on January 22. In recent years, the United States had contributed over 680 million dollars annually, according to the Department of Health and Human Services.
Scientists from the Centers for Disease Control and Prevention virtually attended the influenza strain selection meeting held in Istanbul, Turkey. Daniel Jernigan MD MPH, former director of the agency’s National Center for Emerging and Zoonotic Infectious Diseases, emphasized that continued collaboration remains vital.
United States Viral Samples in Vaccine Selection
Two of the recommended strains for next fall’s vaccines are derived from viral samples collected in Missouri and Pennsylvania, highlighting ongoing involvement by United States scientists. According to Jernigan, this enhances protection against recently circulating influenza B viruses, particularly among children.
The Centers for Disease Control and Prevention gain access to global viral samples, while participating laboratories within the World Health Organization network benefit from specialized testing capabilities. If participation were restricted, both sides would lose valuable contributions.
Redundant Laboratory Networks and Manufacturing Safeguards
Independent laboratories worldwide gather and analyze viral specimens before submitting them to centralized resource databases capable of cultivating these viruses. This redundancy ensures multiple facilities can generate vaccines, providing backup capacity if one laboratory encounters challenges.
Through these international laboratory networks, scientists have been able to monitor the genetic composition of circulating viruses. Numerous academic institutions, laboratories, and vaccine effectiveness networks remain actively engaged in surveillance and evaluation.
Regulatory Decisions and Policy Uncertainty
National authorities typically rely on guidance from the World Health Organization when determining vaccine composition. Historically, the United States Food and Drug Administration has aligned its recommendations accordingly and scheduled a March 12 meeting of its Vaccines and Related Biological Products Advisory Committee to discuss upcoming flu vaccine guidance.
Uncertainty remains regarding whether the Food and Drug Administration will fully adopt the updated recommendations or introduce additional hurdles for manufacturers. Over the past year, public health leaders have faced unexpected policy shifts, including reconsideration of certain childhood vaccine recommendations.
Moderna Messenger Ribonucleic Acid Vaccine Debate
Earlier this month, the Food and Drug Administration initially declined to review Moderna’s messenger ribonucleic acid influenza vaccine, which could potentially shorten manufacturing time from six months to approximately six to eight weeks.
Such accelerated production might enable manufacturers to adjust to late-emerging viral strains and still distribute vaccines before flu season concludes. The agency reversed its decision one week later.
Further complexity surrounds Robert F. Kennedy Jr., current secretary of the Department of Health and Human Services, who has previously expressed opposition to vaccines and made unsupported claims linking flu vaccination to his spasmodic dysphonia.
Recommended Viral Strains for Egg and Cell Based Vaccines
The World Health Organization advised distinct strains depending on manufacturing method. For traditional egg-based vaccines, recommended strains include an A Missouri 11 2025 H1N1 pandemic 2009-like virus, an A Darwin 1454 2025 H3N2-like virus, and a B Tokyo EIS13 175 2025 Victoria lineage-like virus.
For cell culture, recombinant protein, or nucleic acid-based vaccines, the advised strains include an A Missouri 11 2025 H1N1 pandemic 2009-like virus, an A Darwin 1415 2025 H3N2-like virus, and a B Pennsylvania 14 2025 Victoria lineage-like virus.
In conclusion, the complete revision of influenza vaccine strains underscores the dynamic nature of viral evolution, the importance of global laboratory collaboration, and the continuing role of vaccines in reducing severe illness despite emerging variants.
Reference:
- WHO updates all 3 viral strains to be included in fall flu shots(https://www.cidrap.umn.edu/influenza-vaccines/who-updates-all-3-viral-strains-be-included-fall-flu-shots)
Source-Medindia