Rachel V Thomas

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US Flu Cases Rising: What To Know About The New G155E H1N1 Mutation

Flu cases are rising earlier than usual in the US, with influenza A <span>H1N1</span> driving most infections. A new mutation, <span>G155E</span>, may be contributing to the surge.

The 2026-2027 flu season began earlier than usual, with infections increasing as early as August. As of November 5, flu activity was growing or likely growing in 42 states, according to the US Centers for Disease Control and Prevention (<span>CDC</span>).

At least 1.7 million illnesses, 25,000 hospitalisations and 1,400 deaths have been reported so far this season.

“Early-season influenza activity is currently higher than typically observed at this time of year,” the CDC said in its FluView report for the week ending October 31.

<h2>Is The <span rel="noindex">G155E H1N1 Mutation</span> Driving The Surge? </h2>

<strong>Also read: </strong><a href="https://www.healthandme.com/health-news/g155e-h1n1-mutation-in-us-raises-concerns-can-this-years-flu-shot-still-protect-you-article-156374682" data-type="tilCustomLink">G155E H1N1 Mutation In US Raises Concerns: Can This Year’s Flu Shot Still Protect You?</a>

H1N1 is currently responsible for the vast majority of flu cases, marking a shift from last winter, when influenza A H3N2 subclade K, also known as the “superflu”, dominated.

The circulating H1N1 strain has acquired a new mutation called G155E. Early laboratory findings suggest it may make some strains harder for existing antibodies to recognise, potentially helping the virus evade immunity from previous infections or vaccination.

“It is different from last year’s H1N1 virus, and that mutation position (G155E) we know is important for generating protective antibody responses,” <span>Andrew Pekosz</span>, PhD, a virologist at the Johns Hopkins Bloomberg School of Public Health, told TODAY.com.

However, it is not yet clear whether the mutation is contributing to the early surge or making infections more severe.  

“How that (mutation) is going to affect the disease spread and severity is not clear,” Pekosz said.

<h2>Will The Flu Vaccine Protect Against G155E? </h2>

<strong>READ: </strong><a href="https://www.healthandme.com/health-news/flu-activity-rises-early-in-us-uk-and-japan-why-experts-urge-vaccination-before-winter-article-156307089" data-type="tilCustomLink">Flu Activity Rises Early In US, UK And Japan: Why Experts Urge Vaccination Before Winter</a>

The impact of G155E on vaccine effectiveness remains uncertain. The CDC said it was too early to determine whether the mutation would affect protection this season.

The 2026-2027 flu vaccines target three viruses: influenza A H1N1 (pdm09), influenza A H3N2 and influenza B.

Even if the circulating H1N1 strain differs from the vaccine strain, vaccination can still protect against severe illness and other circulating flu viruses.

“Even if there’s a mismatched strain, there’s two other strains that the vaccine will provide better protection against,” Pekosz said.

The American Medical Association recommends annual flu vaccination for everyone aged six months and older, unless medically contraindicated.

<h2>What Are The Symptoms Of H1N1 Flu? </h2>

<strong>Read More: </strong><a href="https://www.healthandme.com/health-wellness/flu-2026-symptoms-to-watch-for-as-new-season-begins-article-156254381" data-type="tilCustomLink">Flu 2026: Symptoms To Watch For As New Season Begins</a>

<ul><li>Fever and chills</li><li>Fatigue</li><li>Body aches</li><li>Runny nose</li><li>Cough</li></ul>

Flu symptoms can overlap with those of COVID-19, making testing important.

Antiviral medications can help reduce the severity and duration of influenza, particularly among people at higher risk of complications, including adults over 65, children under five, and immunocompromised individuals.

“You have to get that prescription fast ... within the first 48 hours after symptom onset, (or else) they don’t work as well,” Pekosz said.

Why Are There Summer & Winter Flu Vaccine Doses? | Expert Explains

Experts say the emergence of G155E is not a reason to panic but reinforces the importance of flu vaccination.

“View (this) as a sign to go out and get the flu vaccine,” Pekosz said.

It takes approximately two weeks for vaccine-induced protection to develop. Annual vaccination remains an important way to reduce the risk of severe flu, complications and hospitalisation. Regular hand hygiene can also help limit the spread of infection.

Flu and COVID-19 vaccines target different viruses. A flu shot does not protect against COVID-19, so eligible people may need separate vaccinations to reduce their risk of severe illness from both infections.

“Flu vaccination doesn't protect just yourself against the risk of having influenza but it also prevents transmission of infection to other vulnerable people around ourselves like little ones, elderly family members and people with medical conditions,” Dr. Bhawna Malik, Senior Consultant-Neonatologist and Pediatric Intensivist at Motherhood Hospitals, Greater Noida, told <strong><em>HealthandMe</em></strong>.

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Flu cases are rising earlier than usual in the US, with influenza A H1N1 driving most infections. A new mutation, G155E, may be contributing to the surge.The 2026-2027 flu season began earlier than usual, with infections increasing as early as August. As of November 5, flu activity was growing or likely growing in 42 states, according to the US Centers for Disease Control and Prevention (CDC).At least 1.7 million illnesses, 25,000 hospitalisations and 1,400 deaths have been reported so far this season.“Early-season influenza activity is currently higher than typically observed at this time of year,” the CDC said in its FluView report for the week ending October 31.Is The G155E H1N1 Mutation Driving The Surge? Also read: G155E H1N1 Mutation In US Raises Concerns: Can This Year’s Flu Shot Still Protect You?H1N1 is currently responsible for the vast majority of flu cases, marking a shift from last winter, when influenza A H3N2 subclade K, also known as the “superflu”, dominated.The circulating H1N1 strain has acquired a new mutation called G155E. Early laboratory findings suggest it may make some strains harder for existing antibodies to recognise, potentially helping the virus evade immunity from previous infections or vaccination.“It is different from last year’s H1N1 virus, and that mutation position (G155E) we know is important for generating protective antibody responses,” Andrew Pekosz, PhD, a virologist at the Johns Hopkins Bloomberg School of Public Health, told TODAY.com.However, it is not yet clear whether the mutation is contributing to the early surge or making infections more severe.  “How that (mutation) is going to affect the disease spread and severity is not clear,” Pekosz said.Will The Flu Vaccine Protect Against G155E? READ: Flu Activity Rises Early In US, UK And Japan: Why Experts Urge Vaccination Before WinterThe impact of G155E on vaccine effectiveness remains uncertain. The CDC said it was too early to determine whether the mutation would affect protection this season.The 2026-2027 flu vaccines target three viruses: influenza A H1N1 (pdm09), influenza A H3N2 and influenza B.Even if the circulating H1N1 strain differs from the vaccine strain, vaccination can still protect against severe illness and other circulating flu viruses.“Even if there’s a mismatched strain, there’s two other strains that the vaccine will provide better protection against,” Pekosz said.The American Medical Association recommends annual flu vaccination for everyone aged six months and older, unless medically contraindicated.What Are The Symptoms Of H1N1 Flu? Read More: Flu 2026: Symptoms To Watch For As New Season BeginsCommon symptoms include:Fever and chillsFatigueBody achesRunny noseCoughFlu symptoms can overlap with those of COVID-19, making testing important.Antiviral medications can help reduce the severity and duration of influenza, particularly among people at higher risk of complications, including adults over 65, children under five, and immunocompromised individuals.“You have to get that prescription fast ... within the first 48 hours after symptom onset, (or else) they don’t work as well,” Pekosz said.When Should You Get Vaccinated?      Experts say the emergence of G155E is not a reason to panic but reinforces the importance of flu vaccination.“View (this) as a sign to go out and get the flu vaccine,” Pekosz said.It takes approximately two weeks for vaccine-induced protection to develop. Annual vaccination remains an important way to reduce the risk of severe flu, complications and hospitalisation. Regular hand hygiene can also help limit the spread of infection.Flu and COVID-19 vaccines target different viruses. A flu shot does not protect against COVID-19, so eligible people may need separate vaccinations to reduce their risk of severe illness from both infections.“Flu vaccination doesn't protect just yourself against the risk of having influenza but it also prevents transmission of infection to other vulnerable people around ourselves like little ones, elderly family members and people with medical conditions,” Dr. Bhawna Malik, Senior Consultant-Neonatologist and Pediatric Intensivist at Motherhood Hospitals, Greater Noida, told HealthandMe.

us flu cases rising: what to know about the new g155e h1n1 mutation

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