2024-2025 Respiratory Disease Season Outlook – October Update

Overview

CDC expects the fall and winter respiratory disease season will likely have a similar or lower number of combined peak hospitalizations due to COVID-19, influenza, and RSV compared to last season. This assessment has not changed since CDC's outlook was initially published on August 29.

As of October 11, overall respiratory virus activity is low nationally. The Respiratory Illnesses Data Channel has weekly updates about current surveillance of respiratory illness.

• COVID-19: COVID-19 activity is declining in most areas. COVID-19-associated ED visits and hospitalizations are decreasing overall. Laboratory percent positivity is 7.7%. Epidemic trend estimates indicate that COVID-19 infections are declining or likely declining in much of the country, as of October 8.
• Influenza: Nationally, seasonal influenza activity remains low. As of October 8, epidemic trend estimates indicate that influenza infections are growing or likely growing in 10 states, declining or likely declining in 9 states, and not changing in 18 states.
• RSV: Nationally, RSV activity remains low. However, signs of increased RSV activity have been detected in the southeastern United States, including Florida, particularly in young children.

This outlook is intended to provide decision-makers with information to assist in public health preparedness during the 2024-2025 fall and winter respiratory virus season, such as when hospitals might prepare for the highest demand.

Our assessments are based on expert opinion, current and historical surveillance data, and scenario modeling for COVID-19, influenza, and RSV. As with all long-range scenarios, there is inherent uncertainty, which we describe below.

Role of vaccination

COVID-19

In our initial outlook, published on August 29, we outlined two potential scenarios for COVID-19 hospitalization burden to demonstrate the range of possibilities for how the season could unfold. While we lack comprehensive hospitalization data for the U.S. summer months because mandatory reporting does not resume until November, other surveillance data suggest these two scenarios (Scenarios A and B) still reflect useful bounds for the coming season. According to data from the COVID-19-Associated Hospitalization Surveillance Network (COVID-NET), the summer wave peaked in the week ending August 10, with an estimated 4.8 hospitalizations per 100,000. As a result, population immunity may be lower than it would be had the summer wave of infection continued to increase or if it peaked at a higher rate. We therefore expect the upcoming season to be more similar to Scenario A, with a winter peak that is higher than the preceding summer/fall peak, similar to COVID-19 trends over the last four years. This scenario model assumes variants will emerge this winter with similar severity and transmissibility to variants that drove last winter's peak, and the 2024-2025 COVID-19 vaccine will have similar effectiveness as last year's vaccine.

Regardless of the exact trajectory, vaccination is expected to play a critical role in preventing hospitalizations due to COVID-19 this season. As of October 5, 11.2% of adults 18 years or older have received the updated 2024-2025 COVID-19 vaccine, and this percentage is expected to increase as the season progresses. To understand the potential impact of vaccinations, we used scenario modeling to compare scenarios for high and baseline vaccine uptake. For our baseline vaccination scenario, we used data from the first week of collection of the National Immunization Survey. As of September 7, 23.9% of adults 18 years or older report that they "definitely will" receive a vaccine this yearA—down from 28.2% during the first week of collection last season (September 30, 2023B), a 15% relative reduction. Prior modeling indicates that vaccine sentiment at the beginning of the season may be predictive of end-of season vaccine uptake.C

Results indicate that if there is a similar 15% reduction in uptake relative to last year, approximately 77,000 to 98,000 hospitalizations would be averted, assuming a 50% and 75% vaccine efficacy against hospitalization, respectively. However, in our high vaccination scenario where uptake is double that of last seasonD—still lower than overall uptake for the influenza vaccine—approximately 179,000 to 227,000 hospitalizations would be averted, assuming a 50% and 75% vaccine efficacy against hospitalization, respectively. For more details on scenario modeling, see our Behind the Model. The COVID-19 Scenario Modeling Hub's latest results showed similar potential impact of vaccination on preventing COVID-19 hospitalizations.

Vaccination coverage and sentiment vary by jurisdiction, age, race and ethnicity, poverty status, health insurance and other social and demographic factors. In addition to protecting vaccinated individuals, maternal vaccination can help protect infants who are not age-eligible for vaccination, but still experience high rates of COVID-19-associated hospitalization.

Influenza

Vaccination is expected to play a key role in preventing influenza illnesses, medical visits, hospitalizations and deaths due to influenza this season. Recent modeling by the Influenza Scenario Modeling Hub indicates that a 20% increase in influenza vaccination compared to last season could lead to a 9–11% reduction in hospitalizations due to influenza this season. During the 2023-2024 influenza season, CDC estimates that influenza vaccination prevented between 105,000 and 240,000 hospitalizations. A recent study in five South American countries during the 2024 Southern Hemisphere influenza season found that the 2024 Southern Hemisphere seasonal influenza vaccine reduced the risk for influenza-associated hospitalization among high-risk groups by 35%.

While we expect influenza vaccination rates to increase as the season progresses, 19.6% of adults 18 years or older have received the 2024-25 seasonal influenza vaccine, as of October 5, up from 16.6% of adults 18 years or older who received the 2023-2024 seasonal influenza vaccine as of October 7, 2023. As of October 5, 27.5% of adults 18 years or older report that they will "definitely" receive a vaccine this year. Vaccination coverage and sentiment vary by jurisdiction, age, race and ethnicity, poverty status, health insurance and other social and demographic factors.

RSV

Immunization is expected to play a key role in preventing hospitalizations due to RSV among infants and older adults this season. As of October 5, 36.9% of adults 75 years or older have ever received the RSV vaccine since it was first available last season, while an additional 13.9% indicate that they definitely will receive the RSV vaccine this year. Vaccination coverage and sentiment vary by jurisdiction, age, race and ethnicity, poverty status, health insurance and other social and demographic factors.

Despite last year being the first year for RSV immunization products, more than half of eligible infants were protected against RSV by maternal vaccination or receipt of the RSV antibody nirsevimab, according to a CDC survey. Early estimates of nirsevimab effectiveness indicated that nirsevimab was 90% effective against RSV-associated hospitalization in infants. As of September 2024, among females with an infant born since April 1, 52.7% reported that they will definitely get nirsevimab for their infant.

Factors, Key Uncertainties, & Methods