October 4, 2024

CFA's Insights for Respiratory Virus Season

CFA is providing insights to support public health planning and response to the fall and winter respiratory virus season. Below, we highlight our current and upcoming products related to respiratory virus season. We will share additional products as the season progresses.

Current Epidemic Trends

CFA provides weekly estimates of R_t, the time-varying reproductive number, at the national and state levels to determine the current epidemic trends. Estimates are currently available for COVID-19 and influenza. R_t is a data-driven measure of disease transmission. R_t can tell us whether infections are growing, declining, or remaining stable, and can help public health practitioners prepare and respond to these viruses – read more about R_t and how we calculate it.

Map of the United States showing each state colored by its epidemic growth status category. — Example of the Epidemic Trend tool. Visit the page to view the current epidemic growth status.

Keep Reading: Current Epidemic Trends (Based on R_t) for States

Improving CDC’s Tools for Assessing Epidemic Trends

CFA is building modeling tools and computational pipelines so that we can analyze data quickly and accurately in response to outbreaks. Our goal is to make these tools accessible to federal, state, tribal, territorial, local, and academic partners. One of these efforts is to estimate the time-varying reproductive number, R_t, a measure that helps us quickly assess whether infections are increasing or decreasing.

Idealized Rt chart. Transmission chain of 3 infected generation persons to 4 infected generation persons. — *R_t* is a data-driven quantity. We identify all the individuals infected on a particular date (this is referred to as the "infectee generation", with four newly infected persons), and divide by the number of people who caused those infections (or the "parents" of those cases, making up the "infector generation").

Keep Reading: Behind the Model: CDC's Tools to Assess Epidemic Trends

Respiratory Disease Season Outlook

CFA led development of the 2024-2025 CDC respiratory disease season outlook to provide decision-makers information to assist with public health preparedness, including planning for potential surges in hospital demand. CDC expects the 2024-2025 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. See the October update to the season outlook. CDC will continue to monitor respiratory disease activity throughout the fall and winter.

Bar chart with past and anticipated peak hospitalization rates for 17-18, 22-23, 23-24, 24-25 respiratory seasons. — Experts believe there’s a roughly 80% chance that the hospitalization burden for COVID-19, influenza, and RSV combined at their peak during the 2024-25 season will be similar to or lower than last season.

Keep Reading: 2024-2025 Respiratory Disease Season Outlook – October Update

How scenario modeling can inform decision-making

CFA has developed scenario modeling capability that allows decision-makers to examine a range of possible outcomes under different assumptions about the future, providing insights for addressing specific policy questions and for general preparedness and planning. Read more for an overview of how scenario modeling helped inform CFA's 2024-2025 Respiratory Disease Season Outlook.

Line chart of historic COVID-19 hospitalizations with ribbons for two possible peaks based on different scenario models. — Two possible scenarios for peak COVID-19 hospitalization depending on timing of summer COVID-19 activity and input data source.

Keep Reading: Behind the Model: How Scenario Modeling Can Inform Public Health Decision-Making.

COVID-19 Forecasts (coming soon)

Previously, CDC has submitted short-term forecasts of COVID-19 hospital admissions to the COVID-19 Forecast Hub. The COVID-19 Forecast Hub, which is currently paused, receives forecasts from modeling teams from across the country and builds a single ensemble forecast. These ensemble forecasts for COVID-19 hospitalizations have helped public health decision-makers anticipate healthcare burden and prepare for potential COVID-19 surges. One of the forecasts CFA submitted was informed by wastewater data – read more about CFA's wastewater-informed COVID-19 hospital admission forecast. COVID-19 hospitalization forecasts are expected to resume this winter.

Line chart showing daily COVID-19 hospital admissions on the y-axis and Feb to May on the x-axis. — Example of a COVID-19 short-term forecast showing the observed number of COVID-19 hospital admissions in black and an ensemble forecast estimating the future number of COVID-19 hospital admissions in red with shaded prediction intervals.

Respiratory Illnesses Data Channel

CFA provides forecasts and analytics to support CDC's wider preparedness efforts for respiratory virus season. Part of the wider effort includes the Respiratory Illnesses Data Channel, which provides a snapshot of COVID-19, influenza, and RSV activity in your community so that you can protect yourself and others.