Is Influenza A (influenza type A) more severe than Influenza B (influenza type B) in terms of symptoms?

From the Guidelines

Influenza A is generally considered to cause more severe symptoms than influenza B, particularly in terms of fever resolution and viral shedding. The severity of influenza symptoms can vary significantly between individuals, but studies have shown that influenza A viruses tend to lead to more intense symptoms, including fever, body aches, headaches, fatigue, and respiratory symptoms [@\1@]. This increased severity is thought to be due to the greater genetic variability of influenza A viruses, which can undergo antigenic shifts and create novel strains to which humans have little immunity. Influenza A is also responsible for most pandemics throughout history.

• Key symptoms of influenza A include:
  • Higher fever
  • More severe body aches
  • Increased fatigue
  • More pronounced respiratory symptoms
• In contrast, influenza B tends to cause milder symptoms, although some cases can still be severe, especially in vulnerable populations like children, the elderly, and those with compromised immune systems.
• Both types of influenza respond to the same antiviral medications, including oseltamivir (Tamiflu) 75mg twice daily for 5 days, which works best when started within 48 hours of symptom onset [@\1@].
• Annual vaccination remains the best prevention strategy against both influenza types, as it can help reduce the severity and risk of complications from influenza infection.

From the FDA Drug Label

There was no consistent difference in treatment effect in subjects with influenza A compared with influenza B; however, these trials enrolled smaller numbers of subjects with influenza B and thus provided less evidence in support of efficacy in influenza B. The FDA drug label does not provide a direct comparison of the severity of symptoms between influenza A and influenza B. No conclusion can be drawn regarding the severity of symptoms between the two types of influenza. 1

From the Research

Comparison of Influenza A and B Symptoms

• The severity of influenza A and B infections in children is similar, with no significant differences in clinical features or outcomes, management, treatment at intensive care unit, or length of stay 2.
• In adult patients, influenza A H3N2 infection was found to be more severe than A H1N1 or B in terms of fever, leukopenia, and C-reactive protein, while gastrointestinal symptoms were more common in influenza B 3.
• There is no clear evidence to suggest that influenza A is more severe than influenza B in terms of symptoms, as the severity of the infection can vary depending on the subtype and the population being studied.

Clinical Features of Influenza A and B

• Fever, myalgia, and other symptoms such as headache, general malaise, and sore throat are equally frequent in influenza A H3N2, A H1N1, and B infections 3.
• Gastrointestinal symptoms such as nausea, epigastralgia, and diarrhea are more prominent in influenza B 3.
• The clinical presentation, outcomes, and management of influenza A and B infections can vary depending on the age group and population being studied 2, 3.

Treatment and Prevention of Influenza

• Neuraminidase inhibitors, such as oseltamivir and zanamivir, are effective in treating and preventing influenza A and B infections 4, 5, 6.
• The use of quadrivalent vaccines containing both lineages of B viruses is recommended for optimal protection against severe influenza illnesses in children 2.
• In geriatric patients, oseltamivir has the most abundant evidence for reducing mortality and complications, while peramivir and baloxavir are alternative options for preventing and treating influenza 6.