A New Antigenically Drifted and Reassorted Influenza B Strain Emerged at the End of the 2025-2025 Flu Season but They Are Only Just Telling Us!
Nikhil Prasad Fact checked by:Thailand Medical News Team Jun 26, 2026 1 hour, 29 minutes ago
Medical News: Scientists Discover a Concerning New Influenza B Virus That Could Challenge Existing Vaccines
Researchers from the Johns Hopkins University School of Medicine, the Johns Hopkins Bloomberg School of Public Health, Johns Hopkins Hospital System, and the Johns Hopkins Center of Excellence for Influenza Research and Response in the United States have identified a newly evolved Influenza B virus that appeared near the end of the 2024–2025 flu season but has only now been fully described. The discovery raises fresh concerns because the virus carries important genetic changes that helped it avoid recognition by antibodies produced after vaccination.
Scientists have identified a newly evolved Influenza B virus capable of escaping much of the immunity generated
by current seasonal vaccines.
Influenza B receives far less attention than Influenza A, yet it causes a significant number of seasonal flu infections every year, especially among children. The newly identified virus belongs to a subgroup known as C.3.1/re and emerged after exchanging genetic material with another influenza B strain while also acquiring additional mutations that altered its surface proteins.
A Virus That Changed in More Than One Way
The scientists found that the new virus did not simply accumulate small mutations over time. Instead, it underwent a process called reassortment, where different influenza viruses swap entire gene segments after infecting the same host. Four of its eight gene segments came from one virus lineage while the remaining four came from another.
One particularly important mutation restored a sugar coating, known as a glycan, on the virus's hemagglutinin protein. This tiny structural change effectively hid an important target that antibodies normally recognize, making it much harder for existing immune defenses to neutralize the virus.
The research team also identified additional mutations in the neuraminidase protein. Although these changes slightly reduced enzyme activity, the virus remained sensitive to the antiviral drug oseltamivir.
Children Were More Frequently Infected
The investigators analyzed influenza cases collected within the Johns Hopkins Hospital System during the late 2024–2025 flu season. Influenza B cases rose dramatically during March and April, with the new C.3.1/re strain rapidly replacing previously dominant viruses in the region.
Patients infected with the new strain were generally younger than those infected by earlier Influenza B variants. The median age was only eight years, compared with thirteen years for infections caused by older circulating strains. However, despite spreading more readily among children, the researchers found no evidence that the virus caused more severe illness or worse clinical outcomes.
Vaccine Concerns
This
Medical News report highlights vacc
ine concerns. One of the study's most striking findings involved how poorly existing antibodies recognized the new virus. The researchers tested blood samples collected before and after seasonal influenza vaccination from 50 volunteers.
Before vaccination, most participants already possessed antibodies capable of neutralizing previous Influenza B strains. However, approximately 84 percent had virtually no detectable neutralizing antibodies against the new C.3.1/re virus. Even after vaccination, about 78 percent still failed to produce measurable protective antibody levels against the emerging strain.
Only one participant showed a strong antibody response against the new virus after vaccination, while responses against the vaccine strain and older Influenza B viruses remained robust.
When the researchers experimentally removed the newly acquired sugar coating from the virus, antibody recognition returned almost completely. This demonstrated that the restored glycan played a major role in helping the virus evade immunity.
Global Spread Is Already Being Observed
Although the virus first became prominent in the eastern United States, surveillance data showed it later appeared in Japan and subsequently spread into other regions. The researchers also detected additional reassorted Influenza B viruses carrying similar immune-evasion mutations, suggesting the virus is undergoing a period of rapid genetic diversification.
The findings also indicate that vaccine strain selection may face increasing challenges because currently circulating viruses continue to evolve in unexpected ways.
Conclusion
The discovery of this newly evolved Influenza B virus demonstrates that seasonal flu viruses continue to change through both mutation and reassortment, allowing them to escape immune protection more effectively than previously recognized. Although the virus does not currently appear to cause more severe disease, its ability to evade vaccine-induced antibodies and spread among children makes it an important public health concern. The study underscores the need for continuous genomic surveillance, faster reporting of emerging strains, and more adaptable vaccine development strategies to keep pace with rapidly evolving influenza viruses before they become widespread.
The study findings were published in the peer reviewed journal: mBio.
https://journals.asm.org/doi/10.1128/mbio.01198-26
For the latest on Influenza B virus, keep on logging to Thailand
Medical News.
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https://www.thailandmedical.news/articles/influenza-or-flu
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