Seasonal influenza: Complications, prevention, and treatment

Seasonal influenza is caused by the influenza virus, which has periodically led to major epidemics worldwide, associated with both high morbidity and increased mortality. In the United States, the number of influenza-related cases and deaths has been rising almost every year over the past three decades. This may be linked to the growing population of individuals over 85 years of age, whose mortality rate is 16 times higher than that of people aged 65–69. Hospital stays for elderly patients have also increased from six to eight days on average.

Each year, influenza causes approximately 35,000 deaths and leads to about 200,000 hospital admissions in the U.S., primarily due to pneumonia and cardiac complications. The rate of hospitalization depends on both the duration of the winter season and the dominant viral strain. Studies show that:

• The A(H1N1) strain causes a relatively mild form of the disease.
• The B strain produces moderate illness.
• The A(H3N2) strain is the most severe, accounting for 99% of hospital admissions (per 100,000 population) and 80% of influenza-related deaths.

High-Risk Groups

Those at greatest risk include:

• Infants under one year old
• Pregnant women
• Adults over 65
• Individuals with chronic health conditions or comorbidities

Prevention

Vaccination remains the cornerstone of influenza prevention and should be administered annually, as the virus mutates and the dominant strain changes each year. Research suggests that people over 65 may not benefit as much from vaccination due to weakened immune systems, whereas younger individuals achieve stronger protection.

Treatment

When started early, antiviral therapy can produce excellent results and significantly reduce the risk of serious complications. However, resistance to drugs such as amantadine and neuraminidase inhibitors may limit their effectiveness.

Common Complications

The most frequent complications of influenza are pulmonary, particularly secondary bacterial pneumonia. These infections—often caused by Staphylococcus aureus, including methicillin-resistant strains (MRSA)—carry a high risk of mortality. Therefore, antibacterial therapy is often prescribed alongside antiviral treatment during the flu season.

Other pathogens such as Klebsiella pneumoniae, Aspergillus, and Pneumocystis jirovecii can also cause pneumonia during influenza infection. Although neuromuscular pain and cardiac complications are less common, they can occur at any age.

Patients with chronic conditions—including heart and lung disease, diabetes, kidney disorders, rheumatoid arthritis, schizophrenia, or a history of stroke—face a significantly higher mortality risk. These individuals are 30 times more likely to require hospitalization and may either recover or succumb to the illness.

Special Populations

Pregnant women generally have lower vaccination rates compared to non-pregnant women. People living with HIV/AIDS may still experience fever and symptoms despite vaccination, though immunization can delay disease progression by up to five months. For this reason, vaccination is recommended for all individuals aged 50 and above.

Organ transplant recipients also face heightened risks:

• 62% greater risk of viral and bacterial pneumonia
• 50% greater risk of transplant rejection and mortality

Conclusion

Protecting oneself and others through vaccination is both a personal and public health responsibility. Annual influenza immunization remains the most effective measure to safeguard individual and community health.

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