Find the updated surveillance report from he U.S. Centers for Disease Control and Prevention (CDC).
Influenza virus (flu)
Influenza is a virus that causes respiratory illness. Anyone can get the flu, but disease is typically more severe in those who are less than 5 years old, over 65 years old, those with chronic medical conditions and pregnant patients. There are different types of seasonal influenza virus, type A and type B, that can circulate. Typically, one type is predominant in a given flu season. Influenza viruses undergo antigenic drift which causes a new subtype of flu virus to circulate each year.
Transmission
Influenza is typically a seasonal virus, which circulates from late fall to early spring. early spring. Influenza (Flu) is primarily transmitted in households and community settings. Flu spreads from person to person predominantly through large-particle respiratory droplets. Indirect transmission via hand transfer of the flu virus from contaminated surfaces or objects to mucosal surfaces of the face (e.g., nose, mouth) is possible. Airborne transmission in the vicinity of an infectious individual may also occur. People are typically contagious for about 48 hours before symptoms occur and for a few days after symptoms start.
Signs & symptoms
Signs and symptoms of flu can vary by age, immune status, and underlying medical conditions. Signs and symptoms of uncomplicated flu include:
- Fever
- Muscle aches
- Headache
- Lack of energy
- Dry cough
- Sore throat
- Nasal congestion
- Possible runny nose
Diagnosis
Flu can be difficult to diagnose based on clinical signs and symptoms alone because they can be like those caused by other viruses or bacteria. A number of tests can help diagnose flu. Available diagnostic tests include rapid antigen testing and reverse transcriptase polymerase chain reaction (RT-PCR). In addition, home influenza tests were authorized by the Food and Drug Administration (FDA) in early 2024.
Prevention strategies
Healthcare settings require multi-faceted approaches to prevent the transmission of flu. Core prevention strategies include vaccination and early treatment, hand hygiene, environmental cleaning with approved products, and engineering controls.
Vaccination
Annual flu vaccination is recommended for all people aged 6 months or older who do not have contraindications. Ideally, people should be vaccinated in September or October. However, vaccination should continue throughout the season as long as flu viruses are circulating. These recommendations are supported by multiple national medical specialty societies—American Academy of Pediatrics, American College of Obstetrics and Gynecology, American Academy of Family Physicians, and the Infectious Diseases Society of America.
No licensed flu vaccine is recommended over another for people under 65 years of age. Adults 65 years and older should preferentially receive a high-dose inactivated, adjuvanted inactivated, recombinant influenza vaccine, or mRNA influenza vaccine when available.
Learn more about available vaccines and additional considerations by age:
- Fluzone High-Dose Trivalent vaccine
- Flublok Trivalent recombinant flu vaccine
- Fluad Trivalent adjuvanted flu vaccine
- FluMist Trivalent live attenuated nasal vaccine
- mFlusiva mRNA vaccine
Coadministration with other vaccines
Flu, COVID-19, and RSV vaccines may be given at the same visit for eligible patients. If the patient prefers to receive each vaccine at a separate visit, there is no minimum waiting period between vaccines.
Treatment
Flu antiviral drugs should be started as soon as possible to treat patients who are hospitalized with flu, very sick with flu but do not need to be hospitalized, and those at higher risk of serious flu complications based on their age or health. People with mild illness not at higher risk of flu complications do not need to be treated with antiviral drugs.
CDC recommends four FDA approved antiviral drugs:
- Oseltamivir phosphate (Tamiflu®)
- Zanamivir (Relenza®)
- Peramivir (Rapivab®)
- Baloxavir marboxil (Xofluza®)
Doctors should not wait for laboratory confirmation to start antiviral treatment. Follow prescribing data for each antiviral medication and consider the potential for drug-drug interactions.
Infection prevention & control
In healthcare facilities, Personal Protective Equipment (PPE) for influenza includes wearing a face mask when caring for the patient, in addition to standard precautions. If the patient needs to leave their room, they must wear a mask.
Adverse events
All adverse events must be reported to the Vaccine Adverse Event Reporting System (VAERS).
