While seasonal influenza (flu) viruses are detected year-round in the United States, flu viruses typically circulate during the fall and winter during what’s known as the flu season. The exact timing and duration of flu seasons varies, but flu activity often begins to increase in October. Most of the time flu activity peaks between December and February, although significant activity can last as late as May. Since the start of the COVID pandemic, the timing and duration of flu activity has been less predictable.
The figure below shows peak flu activity in the United States by month for the 1982-1983 through 2021-2022 flu seasons. The “peak month of flu activity” is the month with the highest percentage of respiratory specimenstesting positive for influenza virus infection during that flu season. During this 40-year period, flu activity most often peaked in February (17 seasons), followed by December (7 seasons), January (6 seasons) and March (6 seasons).
When is flu season in the United States?
In the United States, flu season usually occurs in the fall and winter. While influenza viruses spread year-round, most of the time flu activity peaksbetween December and February. The overall health impact (e.g., infections, hospitalizations, and deaths) of flu varies from season to season. CDC collects, compiles, and analyzes information on influenza activity year-round in the United States and produces FluView, a weekly surveillance report, and FluView Interactive, which allows for more in-depth exploration of influenza surveillance data. The Weekly U.S. Influenza Summary Updateis updated weekly year-round.
How does CDC monitor the progress of flu season?
The overall health impact (e.g., infections, hospitalizations, and deaths) from flu varies from season to season. CDC collects, compiles, and analyzes information on influenza activity year-round in the United States and produces FluView, a weekly surveillance report, and FluView Interactive, which allows for more in-depth exploration of influenza surveillance data. The Weekly U.S. Influenza Summary Update is updated each week.The U.S. influenza surveillance systemis a collaborative effort between CDC and its many partners in state and local health departments, public health and clinical laboratories, vital statistics offices, health care providers, and clinics and emergency departments. Information in five categories is collected from nine different data sources that allow CDC to:
- Find out when and where influenza activity is occurring
- Track influenza-related illness
- Determine what influenza viruses are circulating
- Detect changes in influenza viruses
- Measure the impact influenza is having on hospitalizations and deaths in the United States
These surveillance components allow CDC to determine when and where influenza activity is occurring, determine what types of influenza viruses are circulating, detect changes in the influenza viruses collected and analyzed, track patterns of influenza-related illness, and measure the impact of influenza in the United States. More information about Influenza Surveillance in the United States is available.
Why is there a week-long lag between when influenza surveillance data is collected and when it’s reported?
Influenza surveillance data collection is based on a reporting week that starts on Sunday and ends on the following Saturday of each week. Each surveillance participant is requested to summarize the weekly data and submit it to CDC by the following Tuesday afternoon. The data are then downloaded, compiled, and analyzed at CDC. The data are used to update FluView and FluView Interactiveon the following Friday.
Do other respiratory viruses circulate during flu season?
In addition to flu viruses, several other respiratory viruses also spread during flu season and can cause symptoms similar to those seen with flu infection. These respiratory viruses include rhinovirus (one cause of the “common cold”) and respiratory syncytial virus (RSV), which is the most common cause of severe respiratory illness in young children as well as a leading cause of death from respiratory illness in those aged 65 years and older. Other commonly circulating respiratory viruses include human parainfluenza viruses (HPIV), human metapneumovirus (HMPV), respiratory adenoviruses and human coronavirus. More information about non-influenza respiratory viruses is available.
FAQs
The exact timing and duration of flu seasons varies, but flu activity often begins to increase in October. Most of the time flu activity peaks between December and February, although significant activity can last as late as May.
When is flu season the worst? ›
Seasonal variation in deaths due to influenza or pneumonia in 122 U.S. cities, as a proportion of all causes. In the United States, the flu season is considered October through May. It typically reaches an apex in February, with a seasonal baseline varying between 6.1% and 7.7% of all deaths.
What is the reason for the flu season? ›
Cold temperatures and lower humidity facilitate the survival and transmission of respiratory droplets carrying the virus, particularly in environments with increased indoor gatherings during the colder months. These factors collectively contribute to the surge in flu cases known as flu season.
What is the hardest day of the flu? ›
Day 3: Generally, this day is when flu symptoms tend to peak. You may not be able to get out of bed, experience the most severe symptoms, or spend the day sleeping and recovering. Day 4: Symptoms may slowly start to decrease as your immune system becomes better accustomed to the virus.
Why is the flu so bad this year, 2024? ›
When certain types and strains of the virus show up, it can make some flu seasons worse than others. This flu season, H3N2 – a subtype of influenza A - has been the dominant strain. Health officials say we tend to see a worse flu season with more severe illness when H3 viruses are prominent.
What kills the flu virus in the body? ›
But if you have a severe infection or are at higher risk of complications, your healthcare professional may prescribe an antiviral medicine to treat the flu. These medicines can include oseltamivir (Tamiflu), baloxavir (Xofluza) and zanamivir (Relenza). Oseltamivir and baloxavir are taken by mouth.
When is the flu no longer contagious? ›
Most healthy children and adults with the flu can infect others beginning about one day before developing any symptoms and up to seven days after the symptoms resolve. People with weakened immune systems can remain contagious for up to several weeks.
Is vitamin C good for flu? ›
But taking vitamin C won't prevent you from getting the flu or a cold — or from getting COVID-19. If you take vitamin C regularly and catch a cold or the flu, your symptoms may not be so bad. But if you take vitamin C when you already have a cold or flu, it won't affect how long you're sick or how sick you get.
What's the best medicine for flu? ›
Generic oseltamivir and Tamiflu® are available as a pill or liquid suspension and are FDA approved for early treatment of flu in people 14 days and older. Zanamivir is a powdered medication that is inhaled and approved for early treatment of flu in people 7 years and older.
How many days to quarantine for flu? ›
Note: Not everyone with flu will have a fever. People with suspected or confirmed flu, who do not have a fever, should stay home from work at least 5 days after the onset of symptoms. People with flu are most contagious during the first 3 days of their illness.
You will feel the worst around day 2 or 3, but once you reach day 3, the worst is over. Your immune system is working hard to contain the infection during this stage, so you are less contagious since you are still in the contagious phase of the flu.
What day does the flu peak? ›
Days 2 to 3: When symptoms peak. Flu symptoms usually peak and are at their worst on days 2 and 3. You may not feel well enough to get out of bed and should stay home from work or school to recover and avoid spreading the virus to others.
How long does a flu last? ›
Most symptoms go away in 4 to 7 days. The cough and tired feeling may last for weeks. Sometimes, the fever comes back. Some people may not feel like eating.
What month is flu highest? ›
In the United States, flu season usually occurs in the fall and winter. While influenza viruses spread year-round, most of the time flu activity peaks between December and February. The overall health impact (e.g., infections, hospitalizations, and deaths) of flu varies from season to season.
When does the flu peak in a person? ›
How long the flu lasts can vary. Symptoms generally appear within a few days of infection. They usually peak between days 2 and 4, and most people feel better after 5–7 days.
What is the most common month to get sick? ›
As Dr. Mesrobian mentioned earlier, some viruses peak in the winter months — including colds, flu, RSV and COVID. While you can get sick any time of the year, doctors consider cold and flu season, when infections are highest, from October through March.
What day does the flu get worse? ›
You will feel the worst around day 2 or 3, but once you reach day 3, the worst is over. Your immune system is working hard to contain the infection during this stage, so you are less contagious since you are still in the contagious phase of the flu.
