United States influenza statistics by flu season

Overview of influenza statistics in the United States by flu season

United States influenza statistics by flu season provide a comprehensive overview of the impact of influenza in the U.S. over various flu seasons. Influenza, commonly known as the flu, is a contagious respiratory illness caused by influenza viruses. It can cause mild to severe illness, and at times can lead to death. The Centers for Disease Control and Prevention (CDC) tracks flu activity and provides estimates of the burden of influenza in the United States.

Overview

Influenza seasons in the United States typically occur in the fall and winter, with activity peaking between December and February. However, flu activity can last as late as May. The severity of flu seasons can vary widely from year to year, influenced by factors such as the circulating influenza virus strains, the timing of the season, and the effectiveness of the influenza vaccine.

Influenza Virus Strains

File:H1N1 versus H5N1 pathology.png

Comparison of H1N1 and H5N1 pathology

Influenza viruses are classified into types A, B, C, and D. Human influenza A and B viruses cause seasonal epidemics of disease. Influenza A viruses are further divided into subtypes based on the combinations of the hemagglutinin (HA) and neuraminidase (NA) proteins on the virus surface. For example, the H1N1 and H3N2 subtypes are common in humans. Influenza B viruses are not divided into subtypes but are classified into lineages such as B/Yamagata and B/Victoria.

Flu Season Statistics

The CDC provides annual estimates of the burden of influenza in the United States, including the number of cases, hospitalizations, and deaths. These estimates are based on data collected from various surveillance systems and statistical models.

2019-2020 Season

The 2019-2020 influenza season was notable for its early start and moderate severity. The predominant virus was influenza B/Victoria, which is unusual as influenza A viruses typically dominate. The CDC estimated that there were approximately 38 million flu illnesses, 18 million flu-related medical visits, 400,000 hospitalizations, and 22,000 deaths.

2020-2021 Season

The 2020-2021 flu season was atypical due to the COVID-19 pandemic. Public health measures such as mask-wearing, social distancing, and reduced travel significantly decreased the spread of influenza. The CDC reported historically low levels of flu activity, with an estimated 1,675 flu-related hospitalizations and 600 deaths.

2021-2022 Season

The 2021-2022 season saw a return to more typical flu activity levels, although still lower than pre-pandemic seasons. Influenza A (H3N2) was the predominant virus. The CDC estimated around 9 million flu illnesses, 4 million medical visits, 100,000 hospitalizations, and 5,000 deaths.

Prevention and Control

Annual vaccination is the most effective way to prevent influenza and its complications. The CDC recommends that everyone 6 months and older get a flu vaccine each year. Other preventive measures include practicing good hand hygiene, covering coughs and sneezes, and staying home when sick.

Related Pages

• Influenza vaccine
• Centers for Disease Control and Prevention
• Pandemic influenza