Nikhil Prasad Fact checked by:Thailand Medical News Team Oct 18, 2026 45 minutes ago
A newly emerging version of the H1N1 influenza virus carrying a mutation known as G155E is raising concerns among scientists as the Northern Hemisphere approaches its year-end flu season. Early laboratory findings suggest that certain strains carrying this mutation can partially evade antibodies generated by previous influenza infections, potentially leaving sections of the population more vulnerable despite existing immunity.
Scientists are monitoring emerging H1N1 influenza variants carrying the G155E mutation amid concerns about
reduced antibody recognition ahead of the year-end flu season.
The development comes amid reports of unusually early influenza activity in parts of the United States, United Kingdom, and Japan. Researchers are particularly concerned about the rapid emergence of H1N1 viruses belonging to subclade D.3.1.1, which has become prominent among genetically analyzed influenza samples.
H1N1 Emerges as the Dominant Influenza Subtype
Surveillance findings from the U.S. Centers for Disease Control and Prevention indicate a significant shift in the influenza viruses circulating during the early 2026–2027 season.
Unlike the previous season, when H3N2 played a major role, H1N1 has dominated early genetically characterized samples.
As of September 26, 2026, approximately 96 percent of sequenced influenza-positive samples belonged to H1N1, while H3N2 accounted for only 4 percent. No influenza B viruses were identified among those particular samples.
Scientists have also identified subclade D.3.1.1 as an important emerging H1N1 lineage. Its increasing representation has prompted closer examination of mutations affecting the viral hemagglutinin protein, which enables influenza viruses to attach to human respiratory cells.
G155E Mutation Could Alter Immune Recognition
The G155E mutation involves a change in the hemagglutinin protein, replacing the amino acid glycine with glutamic acid at position 155.
This region is important because antibodies frequently target structures on hemagglutinin to recognize and neutralize influenza viruses.
Changes in these structures can produce antigenic drift, allowing newly circulating viruses to become less recognizable to antibodies developed against earlier strains.
Researchers from the University of Washington identified G155E in 13 of 17 genetically sequenced H1N1 samples collected from hospitals and clinics around Seattle.
Although the sample size was relatively small, the detection of the mutation in approximately 76 percent of these samples attracted attention because it suggested substantial local circulation among the viruses examined.
Importantly, the mutation does not automatically make the virus more transmissible or more dangerous. Its principal demonstrated concern involves altered antibody recognition.
Study Examines Antibodies from 260 Individuals
Researchers at the Fred Hutchinson Cancer Center in Seattle, including influenza specialist Professor Jesse Bloom, investigated how existing human immunity re
sponds to genetically diverse influenza viruses.
Their findings, released as a bioRxiv preprint and awaiting peer review, examined blood samples from 260 individuals in Australia and the United States.
The researchers assessed antibody responses against 148 influenza A strains that had circulated through mid-2026.
This extensive comparison allowed scientists to evaluate differences in antibody recognition across multiple viral variants rather than examining a single emerging strain.
The findings showed that certain viruses carrying G155E were less effectively recognized by existing antibodies.
This
Thailand Medical News report highlights an especially important observation: reduced antibody recognition was not uniform across the population, suggesting that previous influenza exposure histories may strongly influence susceptibility to emerging variants.
Teenagers and Young Adults Show Weaker Antibody Recognition
One particularly concerning finding involved teenagers and young adults, whose antibodies demonstrated comparatively poor recognition of some G155E-containing viruses.
Researchers suggested that this pattern could reflect differences in immune history.
Older individuals may have encountered historical H1N1 strains possessing antigenic characteristics resembling those of emerging variants, potentially providing broader recognition.
Younger people, however, may have developed immunity primarily against more recently circulating strains with different antigenic profiles.
This phenomenon illustrates how influenza immunity depends not simply on previous exposure but also on which viral variants individuals encountered throughout their lives.
Nevertheless, reduced laboratory antibody recognition does not necessarily translate into proportionately higher infection rates, hospitalization risks, or severe disease.
Questions Surround the 2026–2027 Influenza Vaccines
Another concern involves the antigenic compatibility of circulating H1N1 variants with this season's influenza vaccines.
The A/Missouri/11/2025-like H1N1 reference strain is included in the recommended 2026–2027 Northern Hemisphere vaccine composition.
However, surveillance and vaccine characterization findings suggest that some viruses within the emerging D.3.1.1 lineage demonstrate reduced antigenic reactivity against this reference strain.
Such findings raise the possibility of diminished protection against infection if circulating viruses differ substantially from vaccine components.
Nevertheless, laboratory antigenic differences cannot establish actual vaccine effectiveness.
Vaccination may continue providing meaningful protection against hospitalization, complications, and severe illness through immune responses extending beyond the antibodies measured in individual laboratory experiments.
Influenza Activity Begins Earlier Than Expected
The emerging H1N1 developments coincide with reports of influenza activity appearing earlier than expected in several countries.
Parts of the United States, particularly the West Coast, have reported increased positive influenza detections during early autumn.
The United Kingdom has also experienced indications of rising influenza activity. Meanwhile, Japan recorded outbreaks during August and September, with some schools temporarily closing shortly after reopening following summer vacations.
These developments have generated concern about whether influenza circulation could intensify before the traditional winter peak.
However, scientists caution that early outbreaks do not necessarily predict the eventual severity or duration of the entire influenza season.
European Surveillance Reveals a Mixed Picture
European health authorities are also monitoring emerging H1N1 variants, including viruses carrying G155E.
According to the European Centre for Disease Prevention and Control, influenza activity remained relatively low across much of Europe during early October.
ECDC virologist Dr. Iva Bråberg reported modest increases in influenza detections, including some hospital-based surveillance indicators.
Denmark and Spain recorded increasing respiratory virus activity in primary care settings.
In Greece, none of 27 reported influenza tests returned positive results, although the limited sample size prevents meaningful conclusions about broader circulation.
Most detected influenza viruses belonged to influenza A, while hospitalized patients were predominantly adults aged 65 and older.
The ECDC emphasized that widespread, unusually early influenza circulation had not yet been established across Europe.
Continued Surveillance and Vaccination Remain Essential
The emergence of G155E illustrates influenza's continuing ability to evolve around existing population immunity. Although laboratory evidence identifies potentially important changes in antibody recognition, scientists still lack sufficient clinical evidence to determine whether these variants will produce more infections, greater disease severity, or substantially reduced vaccine protection. Continued genomic surveillance, real-world vaccine effectiveness studies, and timely vaccination will therefore remain essential as the 2026–2027 influenza season progresses.
References:
https://www.biorxiv.org/content/10.64898/2026.09.15.751855v2
https://www.cdc.gov/fluview/surveillance/2026-week-40.html
https://www.gov.uk/government/statistics/national-flu-and-covid-19-surveillance-reports-2026-to-2027-season/national-flu-and-covid-19-surveillance-report-15-october-2026-week-42
https://cdn.who.int/media/docs/default-source/influenza/who-influenza-recommendations/vcm-southern-hemisphere-recommendation-2027/a.-25-september-2026-recommended-composition-of-influenza-virus-vaccines-for-use-in-the-2027-southern-hemisphere-influenza-season---full-report.pdf?sfvrsn=30f1352f_7&download=true
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