What to Expect This Winter: The CDC's Forecast for Cold Season Respiratory Illness

The Centers for Disease Control and Prevention (CDC) expects this winter's respiratory illness season to produce similar peak hospitalization numbers as last year, combining COVID-19, influenza, and respiratory syncytial virus (RSV) cases. However, a new influenza strain is spreading rapidly across the country, and vaccination rates are lagging behind previous years.

As of December 19, 2025, respiratory illness activity remains at low levels nationally, but the CDC is closely monitoring three key viruses that typically surge during fall and winter months. The agency updates its seasonal outlook every two months to help hospitals and healthcare systems prepare for potential surges in patient demand.

What's Driving This Winter's Respiratory Illness Patterns?

Three main respiratory viruses are shaping this season's outlook, each following distinct patterns across different regions of the United States. COVID-19 activity remains low nationally, though infections are growing or likely growing in 31 states as of December 16. Meanwhile, influenza activity continues to increase across the country, with infections growing or likely growing in 47 states.

RSV activity is increasing primarily in the Southeastern, Southern, and Mid-Atlantic areas, with emergency department visits and hospitalizations rising among children ages 0-4 years old. As of December 16, RSV infections are growing or likely growing in 32 states.

Why Is This Year's Flu Season Different?

A new influenza strain called "subclade K" has emerged as the dominant virus this season, representing approximately 90% of influenza A(H3N2) viruses that the CDC has genetically characterized since late September. This new subclade differs from other circulating influenza viruses, including the virus selected for the 2025-26 seasonal flu vaccines.

The CDC estimates there have been at least 7,500,000 flu illnesses, 81,000 hospitalizations, and 3,100 deaths from flu so far this season. Five influenza-associated pediatric deaths were reported during the week ending December 20, bringing the season total to eight reported flu-related pediatric deaths.

Current surveillance data shows concerning trends in flu activity:

• Virus Dominance: Influenza A(H3N2) viruses account for 91.8% of subtyped influenza A viruses, with subclade K representing 89.5% of characterized samples
• Geographic Spread: All ten Health and Human Services regions show increasing percentages of respiratory specimens testing positive for influenza virus
• Laboratory Positivity: Region 8 had the highest percent positivity at 34.9%, while Region 9 had the lowest at 10.8%

Are Vaccination Rates Keeping Up?

Vaccination coverage is falling short of last year's numbers for both COVID-19 and influenza. As of December 6, only 15.3% of adults 18 years or older have received the updated 2025-2026 COVID-19 vaccine, compared to 19.2% at the same time last year. Approximately 130 million doses of influenza vaccine have been distributed in the United States this season.

The CDC expects vaccination to play a critical role in preventing hospitalizations due to COVID-19 this season, particularly among older age groups. Despite the emergence of subclade K, which differs from the vaccine strain, annual flu vaccination remains the best protection against severe illness.

Healthcare experts emphasize that prescription flu antiviral drugs can treat flu illness when started early and are especially important for patients at higher risk for flu-related complications. The CDC recommends that everyone 6 months and older who has not yet been vaccinated this season get an annual influenza vaccine.