2024-2025 Seasonal Influenza Resource Center for Health Care Personnel

Influenza is a highly contagious respiratory viral infection. There are four types of influenza virus: A, B, C, and D. Type A influenza viruses are the only known type to cause flu pandemics. Influenza B viruses generally cause milder disease and affects humans only. Influenza C is rarely reported as a cause of human illness and has not been associated with epidemic disease. Influenza D is not known to cause illness in humans. Annual epidemics of influenza typically occur between October - March in the Northern Hemisphere and April – September in the Southern Hemisphere.

Influenza is transmitted person to person via large droplets that are expelled when a person coughs or sneezes. These droplets can land in the mouths or noses of people who are nearby or possibly be inhaled into the lungs. Less often, a person might get flu by touching a surface or object that has flu virus on it and then touching their own mouth, nose, or possibly their eyes. Transmission can occur from the day before symptoms begin until about five days after symptoms begin in adults, or up to seven days or more after symptoms begin in children.

Annually, influenza related illness affects between 3 percent and 11 percent of the population in the United States. Between 2010 and 2023, CDC estimates that flu has resulted in 9.3 million – 41 million illnesses, 100,000 – 710,000 hospitalizations and 4,900 – 51,000 deaths annually. Classic symptoms of Influenza include abrupt onset of fever, cough, muscle pain, sore throat, runny nose, headache, and fatigue. These symptoms generally last from 3 to 7 days, however some people may experience a cough or weakness for several weeks. In addition, some people may develop complications, such as bacterial pneumonia, sinus infections, and worsening of chronic medical conditions. Older adults, very young children, pregnant persons, immunocompromised individuals, and those with chronic medical conditions are particularly vulnerable to serious influenza related complications.

Annual influenza vaccination is the best way to protect yourself from flu and is recommended for all persons aged ≥6 months without contraindications. For most people, September and October are the ideal times to be vaccinated against influenza to provide the best protection through the peak season. Ideally, everyone should be vaccinated by the end of October, but immunization is recommended as long as flu activity is reported in the community.

Source: Influenza (Flu) | CDC

Resource Center

You will find below all of the resources you will need for the 2024-25 influenza season. More will be added as they are published or released.

See information on Southern Hemisphere influenza vaccine here