Weekly US Influenza Surveillance Report: Key Updates for Week 1, ending January 10, 2026

The CDC’s weekly surveillance report provides a detailed status update on influenza activity in the United States for the period ending January 10, 2026. While seasonal transmission remains widespread, the data suggests a recent stabilization or decline in cases, though experts remain cautious about a potential post-holiday resurgence. The report highlights that Influenza A(H3N2) is currently the dominant strain and notes a concerning trend of high severity among pediatric patients. Critical statistics reveal that a vast majority of childhood fatalities occurred in individuals who were not fully immunized. Furthermore, the document monitors hospitalization trends, virus mutations, and the continued effectiveness of antiviral treatments. Overall, health officials emphasize that vaccination remains the primary defense as the season progresses.

The 2025-2026 influenza season is currently classified by the CDC as having moderate severity across all ages. However, when examined by specific age groups, the pediatric population (0-17 years) is classified as having high severity, while adults and older adults remain in the moderate category.

Compared to historical trends since the 2010-2011 season, the current season shows several notable indicators of high activity:

• Hospitalization Rates: The overall weekly influenza-associated hospitalization rate peaked at 12.6 per 100,000 population in Week 52. This represents the second highest peak weekly rate recorded since the 2010-2011 season.
• Cumulative Impact: The cumulative hospitalization rate as of Week 1 was 50.4 per 100,000 population, which is also the second highest cumulative rate recorded at this point in a season since 2010-2011.
• Pediatric Severity: Children younger than 18 years have been particularly affected, experiencing the highest peak weekly hospitalization rate observed since the 2010-2011 season. The cumulative hospitalization rate for children is currently the second highest since that same period.
• Burden of Illness: CDC estimates that there have already been at least 18,000,000 illnesses, 230,000 hospitalizations, and 9,300 deaths due to the flu this season.
• Pediatric Mortality: A total of 32 influenza-associated pediatric deaths have been reported for the 2025-2026 season. Notably, among children with known vaccination status, 90% of those who died were not fully vaccinated.

The season has been dominated by Influenza A(H3N2) viruses, which are the most frequently reported so far. While activity remains elevated nationally, it has decreased or remained stable for two consecutive weeks as of early January 2026; however, the CDC continues to monitor for a potential second period of increased activity typically seen after the winter holidays.

The most frequent influenza A virus subclade this season is subclade K, which belongs to the Influenza A(H3N2) subtype.

According to genetic characterization data from the CDC, as of early January 2026, 90.9% (497 out of 547) of the A(H3N2) viruses tested since September 28, 2025, belong to this specific subclade. All of these viruses are further categorized within the HA Clade 2a.3a.1.

For broader context regarding circulating influenza A viruses:

• Influenza A(H3N2) is the dominant virus type overall, accounting for 87.8% of the subtyped influenza A specimens in public health laboratories.
• The A(H1N1)pdm09 subtype is less frequent, making up 12.2% of subtyped specimens. Within this subtype, the genetic distribution is split almost evenly between subclades D.3.1 (49.5%) and D.3.1.1 (49.5%).
• Despite the prevalence of subclade K, antigenic characterization suggests that only a small portion (3.9%) of A(H3N2) viruses are well-recognized by the ferret antisera representing the current vaccine component, indicating significant antigenic drift in this subtype.

The CDC uses these genetic and antigenic characterizations to monitor how well circulating viruses match current vaccines and to track evolutionary changes in the virus.

The CDC categorizes influenza severity for the pediatric group (ages 0–17 years) using an in-season severity assessment framework. This framework assesses severity across three specific age groups: pediatric, adult (18–64 years), and older adults (≥65 years).

For the current 2025–2026 season, the CDC has categorized the pediatric group as having high severity. This classification is based on several critical data points tracked through their surveillance systems:

• Hospitalization Rates: Children younger than 18 years have experienced the highest peak weekly hospitalization rate observed since the 2010–2011 season. Additionally, the cumulative hospitalization rate for children is currently the second highest recorded at this point in a season since 2010–2011.
• Mortality: As of January 10, 2026, a total of 32 influenza-associated pediatric deaths have been reported for the season. The CDC notes that among children eligible for vaccination with a known status, 90% of those who died were not fully vaccinated.
• Weekly Re-evaluation: These severity assessments are conducted every week during the flu season. Because the framework is dynamic, the "high severity" classification for the pediatric group can change if influenza activity increases or decreases significantly.

While the pediatric group is classified as having high severity, the CDC currently classifies the season as moderate across all ages, with both the adult and older adult categories remaining in the moderate range.