A 'super flu' strain is making everyone sick. Is this year's vaccine effective? A new, fast-spreading flu strain is gaining a reputation as a monstrous 'super flu'. The mutation of influenza A(H3N2) called subclade K is driving up infections across the country, including in New Jersey, where the season's first pediatric flu death was reported. The Centers for Disease Control and Prevention estimates that there have been at least 180,000 hospitalizations and 7,400 deaths from flu so far this season. The majority of infections have been driven by influenza A(H3N2) viruses, specifically subclade K. This strain accounts for 91.5% of the influenza A(H3N2) viruses that have undergone additional testing at the CDC. But here's where it gets controversial: why does the flu seem worse this year? Flu viruses are constantly changing and mutating. Each year, researchers analyze data to try and predict which flu strains will be most common during the upcoming season and develop a vaccine to target those selected strains. However, occasionally there are some genetic differences between the circulating viruses and the strains targeted by the vaccine. This is what makes subclade K so stubborn. Dr. Adeel Butt, an infectious disease expert, explains, 'This is a strain that evolved after the vaccine had been prepared earlier last year. So, the vaccine may not fully cover the influenza this year.' The selection of viruses used in this season’s flu vaccines was made in February 2025. Subclade K, however, didn’t emerge until August 2025. According to the World Health Organization, subclade K viruses have several changes from related A(H3N2) viruses, which are already associated with lower vaccine effectiveness. However, current epidemiological data doesn’t indicate an increase in disease severity, although the WHO said 'this subclade marks a notable evolution in influenza A(H3N2) viruses.' Is the vaccine still effective? Even if there are some differences between the flu strains circulating right now and the strains included in the vaccine, preliminary data suggests the shot is still effective to a strong degree. Data from the UK Health Security Agency shows the 2025-2026 vaccine is currently 70 to 75% effective at preventing hospital attendance in children aged 2 to 17 years and 30 to 40% effective in adults. The numbers line up with what Dr. Daniel Ruderfer is seeing at K. Hovnanian Children’s Hospital. He says, 'What we do find year in and year out is that those who get the flu vaccines really have better outcomes overall.' However, national flu vaccination coverage is on the decline for children, something that Ruderfer finds concerning. During the 2024–2025 flu season, vaccination coverage was 49.2% among children 6 months through 17 years, down from 55.4% the previous season and 63.7% during the pre-pandemic 2019–20 season, according to the CDC. Can you still get sick? While vaccines may not fully protect everyone, public health experts say they’re still proven to help prevent serious illness and death. In the average flu season, vaccines have a 40-60% efficacy in reducing the incidence of severe illness, according to the CDC. Dr. Butt, who has more than three decades of experience in infectious diseases, says, 'I want to be very clear, vaccination is still the best way to protect ourselves and the population against influenza and severe illness related to influenza.' There’s a common misconception that getting the flu shot will give you the flu. However, Butt says that’s not possible 'because none of the vaccines recommended by the CDC contain active, live virus.' Flu vaccines may use viral proteins, inactivated viruses, or even small portions of the virus capsule to teach the immune system how to fight off germs. But they don’t contain the active flu virus. So, the vaccine can’t completely prevent infection, but it does reduce your chances of getting infected. Its main strength is preventing the worst-case scenario — severe illness and death. Is there still time to get a flu shot? Yes! The good news is that it’s not too late to try and prevent getting sick. The bad news is that’s because flu season is far from over. While you can get sick with the flu any time of year, the CDC technically defines flu season as running from October to May. Currently, nearly 15 states are in the CDC’s highest possible tier of flu activity. The elevated activity is expected to continue for several weeks. Flu vaccines are available for use in people aged 6 months and older. They’re offered at doctor’s offices, pharmacies, community health clinics, health departments and other community locations. Visit the CDC website for additional help finding vaccines in your area.
