Essential Insights and Data on Influenza

Influenza, commonly known as the flu, is a highly contagious respiratory infection caused by viruses targeting the nose, throat, and occasionally the lungs. The flu predominantly spreads through close contact, with individuals being most infectious during the initial three to four days after symptoms emerge.

The onset of flu symptoms is often abrupt, manifesting as fatigue, muscle aches, chills, coughing, sore throat, and fever. While many recover without intervention, influenza can sometimes lead to severe complications and even death.

Flu viruses disseminate through airborne droplets expelled when an infected person coughs, sneezes, or talks. These droplets can be inhaled directly or transferred via contaminated surfaces to the eyes, nose, or mouth. Transmission can occur within approximately six feet of an infected individual.

As of the article's publication, influenza activity in the U.S. during the 2018-2019 season remained low, with outpatient visits for flu-like symptoms slightly rising to 1.7%, still below the national threshold of 2.2%.

Conversely, the 2017-2018 flu season was notably severe, marked by elevated outpatient and emergency department visits and increased hospitalizations due to influenza.

Continue reading to discover more detailed flu facts and statistics.

Prevalence

Influenza viruses are categorized into four types: A, B, C, and D. Human influenza A and B viruses are responsible for seasonal outbreaks each winter in the United States.

Influenza C typically causes mild respiratory symptoms and does not usually trigger epidemics, whereas influenza D primarily affects cattle and is not known to infect humans.

The majority of flu cases are mild, requiring no medical treatment or antiviral medication, with recovery occurring within two weeks. However, certain groups face a higher risk of serious flu complications, including:

• Children under 5 years, especially those younger than 2
• Adults aged 65 and older
• Residents of nursing homes and long-term care facilities
• Pregnant women and those up to two weeks postpartum
• Individuals with weakened immune systems
• People with chronic conditions such as asthma, heart disease, kidney or liver disease, and diabetes
• Individuals with a body mass index (BMI) of 40 or higher

Since 2010, annual flu cases in the U.S. have ranged from 9.3 million to 49 million, affecting approximately 5% to 20% of the population each year.

Influenza leads to an estimated 31.4 million outpatient visits and over 200,000 hospitalizations annually.

The 2017-2018 season, one of the longest and most severe in recent history, saw over 900,000 hospitalizations and more than 80,000 deaths attributed to the flu.

By late October 2018, the CDC reported 185 pediatric deaths during the 2017-2018 season, with about 80% occurring in unvaccinated children.

Adults aged 65 and older bore the brunt of the last season’s impact, accounting for approximately 58% of hospitalizations.

Economic Impact

Influenza imposes a significant economic burden, costing roughly $10.4 billion annually in direct medical expenses and an additional $16.3 billion in lost productivity.

Flu-related absenteeism accounts for around 17 million missed workdays each year in the U.S., translating to an estimated $7 billion in lost wages and productivity.

According to employment consultants Challenger, Gray & Christmas, the 2017-2018 flu season resulted in over $21 billion in productivity losses, with approximately 25 million workers affected and an average wage loss of $855.68 per sick employee.

A 2018 analysis estimated the total economic burden of seasonal influenza on the American healthcare system and society at $11.2 billion annually, including $3.2 billion in direct medical costs and $8 billion in indirect costs.

Vaccination

The most effective strategy to prevent influenza is annual vaccination, recommended by the CDC for everyone aged six months and older.

Flu vaccines are available as injections or nasal sprays. The traditional egg-based manufacturing process has been used for over seven decades, while newer cell-based and recombinant technologies have been approved in recent years to enhance vaccine production.

Although flu vaccines are not 100% effective, they remain the best defense, reducing the risk of illness by 40% to 60% during well-matched seasons.

During the 2016-2017 season, vaccination prevented an estimated 5.3 million flu cases, 2.6 million medical visits, and 85,000 hospitalizations.

Research indicates that vaccination halves the risk of flu-related death among children with high-risk conditions and reduces the risk by nearly two-thirds in healthy children.

Vaccinated adults hospitalized with flu are 59% less likely to experience severe illness requiring intensive care compared to unvaccinated individuals.

The 2017-2018 flu vaccine demonstrated approximately 40% effectiveness against influenza A and B viruses, lowering the likelihood of seeking medical care for flu symptoms by the same margin.

Vaccination coverage among children aged 6 months to 17 years has remained steady but below the 80% public health target, with a coverage rate of 57.9% during the 2017-2018 season. Adult vaccination coverage was 37.1%, down 6.2 percentage points from the previous year.

For the 2018-2019 season, manufacturers anticipated the availability of up to 168 million flu vaccine doses in the U.S.

Complications and Mortality

While most recover from the flu within days to two weeks, high-risk individuals may develop complications such as:

• Pneumonia
• Bronchitis
• Asthma exacerbations
• Sinus infections
• Heart issues
• Ear infections

Influenza is a leading cause of pneumonia, especially among young children, the elderly, pregnant women, and those with chronic health conditions or residing in nursing homes. In 2016, influenza and pneumonia ranked as the eighth leading cause of death in the U.S.

Adults aged 65 and older face a significantly higher risk of severe flu complications, with bacterial co-infections occurring in 2% to 65% of flu cases according to a 2016 report.

Between 70% and 85% of seasonal flu-related deaths and 50% to 70% of hospitalizations occur within this age group.

In addition to vaccination, the CDC advises preventive measures such as avoiding contact with sick individuals, covering coughs and sneezes, and frequent handwashing.

If infected, antiviral medications prescribed by healthcare providers can reduce illness severity and duration, potentially preventing hospitalization.

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