The United States is experiencing a severe influenza season, characterized by a dominant H3N2 variant, increasing hospitalizations, and a rise in pediatric deaths. Early indicators from the Southern Hemisphere and Europe suggested a challenging season, with U.S. health officials and experts observing a surge in cases and expressing concerns regarding a less optimal vaccine match for the prevalent strain and a decline in vaccination uptake.
Overview of the Current Season
The current influenza season in the United States has seen escalating activity, with approximately 20 million illnesses, 270,000 hospitalizations, and 11,000 deaths reported, including 52 pediatric fatalities. This represents a substantial increase from earlier estimates in December and January.
Flu-like respiratory illnesses accounted for 8.2% of doctor visits at one point, marking the highest rate for that period since the 1997-98 season. Colorado, among other states, has reported a significant increase in flu hospitalizations, particularly among children, and recorded its first pediatric flu death of the season.
The season's trajectory aligns with patterns observed in the Southern Hemisphere, which experienced notable and longer-duration flu activity, and with Europe, where the flu season commenced earlier than typical with high activity in December. The Centers for Disease Control and Prevention (CDC) has identified the current season as the most severe since 2018.
Dominant Strains and Vaccine Efficacy
The H3N2 virus, specifically subclade K, has emerged as the dominant flu strain circulating in the Northern Hemisphere, including the U.S. H3N2 viruses are generally associated with higher activity and a greater incidence of severe disease. This new variant may enable the virus to circumvent existing immunity from previous infections or vaccinations, potentially resulting in a less optimal match for the current flu vaccine.
Despite the potential for a less optimal match, health experts and data suggest that the flu vaccine still offers protection against severe outcomes.
Data from the U.K. indicate vaccine effectiveness of approximately 70% to 75% against hospitalization in children and 30% to 40% against hospitalization in adults. Early data from the Southern Hemisphere suggest that vaccinated children may have a 50% to 75% lower likelihood of hospitalization due to flu this season. Epidemiologists have stated that while protection against the new variant might be reduced, vaccination is still expected to offer significant benefits and remains effective at preventing severe illness.
Impact on Specific Demographics
The season has shown a notable impact on children. Colorado has reported increased flu hospitalizations among children, and the state recorded its first pediatric flu death. Nationally, 52 pediatric deaths have been reported this season.
The previous season (2024-2025) recorded 279 influenza-associated pediatric deaths, the highest number reported to the CDC outside of a pandemic since record-keeping began. Children are particularly advised to receive the flu shot.
Vaccination Landscape and Public Health Messaging
Health officials continue to advise individuals who have not yet received a flu shot to do so promptly, as immunity typically develops within two weeks. Vaccination is emphasized for young children and older adults.
However, concerns have been expressed regarding potentially lower uptake of flu vaccines this year. As of early December, approximately 130 million flu vaccines had been distributed in the U.S., a decrease of 13 million compared to the same period in the previous year. Current vaccination rates stand at 42.5% for children and 43.5% for adults, representing a decrease from the 2019-20 season's peak rates of 63.7% for children and 48.4% for adults.
In early January, flu vaccine recommendations for children transitioned to a "shared clinical decision-making" model.
Robert F Kennedy Jr, Secretary of the US Department of Health and Human Services, suggested that fewer children getting vaccinated might be "a better thing," asserting a lack of scientific evidence for the flu vaccine's efficacy in preventing severe illness, hospitalizations, or death in children. This statement was made despite existing studies, including those from the CDC, indicating the vaccine's effectiveness.
Mehmet Oz, Administrator for the Centers for Medicare & Medicaid Services, also questioned the effectiveness of flu vaccines. The CDC's public statements have characterized the decision to vaccinate as a "personal one," advising individuals to consult their doctors regarding "potential risks and benefits." Additionally, a "Wild to Mild" public vaccination campaign was discontinued, and top health officials have not publicly received vaccinations.
Contributing Factors and Prevention
Factors potentially contributing to the current surge in flu activity include the aggressive nature of the dominant H3N2 strain, a decline in vaccination rates, and the new variant's potential to circumvent existing immunity. Cold weather may also contribute by increasing indoor gatherings, which facilitates virus spread.
Preventative measures against illness include:
- Frequent hand washing.
- Keeping sick family members home until fevers have been absent for at least 24 hours.
- Avoiding gatherings if someone is actively ill.
- Getting vaccinated.
- Mask-wearing.
- Improved ventilation.
- Covering coughs and sneezes.
Antiviral Treatments
Antiviral treatment usage among hospitalized flu patients has declined, from 90% in 2018-19 to 79% in 2022-23. The reduction was more pronounced in children. Experts advise that patients sick enough to seek medical care, as well as those with underlying conditions, pregnant individuals, and older people, should receive antivirals, which are effective against the current variant and should be started promptly after a positive test.
Season Outlook and Emerging Concerns
Medical experts anticipate several more months of flu activity and suggest the potential for a "second peak" in cases. This resurgence is attributed to multiple circulating influenza strains, with influenza B cases reportedly increasing nationally as influenza A H3N2 continues to circulate. Individuals who have previously contracted influenza A can still contract influenza B during the same season, for which the flu vaccine is designed to protect against multiple strains.
Hospital resources are also facing strain from high rates of COVID-19 and RSV, though Colorado has not experienced a "tripledemic" this season as RSV activity remains low. An ongoing concern is the H5N1 bird flu, which continues to affect flocks across the U.S., raising the risk for two flu variants to combine and create a deadlier variant through a process called reassortment.