What is the difference between Influenza B and Influenza A?

From the Guidelines

Influenza A and Influenza B are two distinct types of influenza viruses that cause seasonal flu, with Influenza A being more common, genetically diverse, and capable of causing both seasonal epidemics and global pandemics, whereas Influenza B primarily affects humans, mutates more slowly, and typically causes less severe illness. The key differences between Influenza A and Influenza B lie in their genetic diversity, host range, and mutation rates. Influenza A viruses are categorized into subtypes based on hemagglutinin (HA) and neuraminidase (NA) surface antigens, and have been responsible for global pandemics, such as the 2009 H1N1 pandemic 1. In contrast, Influenza B viruses are separated into two distinct genetic lineages, Yamagata and Victoria, but are not categorized into subtypes, and undergo antigenic drift less rapidly than influenza A viruses 1. Some of the main similarities and differences between Influenza A and B include:

• Both cause similar symptoms, including fever, cough, sore throat, body aches, and fatigue
• Both are targeted by seasonal flu vaccines, which typically protect against both Influenza A and B strains
• Treatment for both types includes antiviral medications, such as oseltamivir (Tamiflu)
• Influenza A has a wider host range, including humans, birds, and pigs, allowing for genetic reassortment and the emergence of new strains
• Influenza B primarily affects humans and mutates more slowly than Influenza A. It is essential to note that the trivalent influenza vaccines available in recent seasons have contained one influenza B virus, representing only one lineage, which may not provide adequate protection against circulating influenza B viruses of the other lineage 1.

From the FDA Drug Label

Of 1,164 subjects with confirmed influenza, 89% had influenza A and 11% had influenza B. 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. Of 346 subjects with confirmed influenza, 65% had influenza A and 35% had influenza B.

The difference between Influenza B and Influenza A is not explicitly stated in terms of clinical characteristics or treatment outcomes in the provided drug label. However, it can be noted that:

• Influenza A was more prevalent in the studied population, accounting for 89% of confirmed influenza cases in one trial and 65% in another.
• Influenza B accounted for 11% and 35% of confirmed influenza cases in the respective trials. No conclusion can be drawn regarding the difference between Influenza B and Influenza A based on the provided information 2.

From the Research

Differences between Influenza B and Influenza A

• Influenza A and B are both responsible for significant morbidity and mortality, with influenza A being more prevalent in certain years or locations 3.
• The main difference between the two is the type of antiviral agents that are effective against them. Adamantanes, such as amantadine and rimantadine, are only effective against influenza A, while neuraminidase inhibitors, such as zanamivir and oseltamivir, are effective against both influenza A and B 3, 4.
• Influenza B is not affected by adamantanes, making neuraminidase inhibitors the primary treatment option for this type of influenza 5.
• Both influenza A and B can be treated with neuraminidase inhibitors, which work by inactivating the viral neuraminidase enzyme, limiting the extent of infection and speeding recovery from illness 4, 6.
• The emergence of resistant mutants is a significant challenge to the effectiveness of antiviral agents, with adamantanes being rendered ineffective due to resistance and neuraminidase inhibitors also being susceptible to resistance 7, 5.

Treatment and Prevention

• Vaccination is the most effective public health measure to combat influenza, with trivalent inactivated vaccine (TIV) and live attenuated influenza vaccine (LAIV) being available 5.
• Antiviral agents, such as neuraminidase inhibitors, can reduce the duration of fever and illness by one to two and one-half days and also reduce the severity of some symptoms, but must be used within 48 hours of the onset of influenza symptoms 3, 4.
• The use of antiviral agents is particularly important in high-risk patients, such as the elderly or those with comorbidities, to reduce mortality and morbidity 5.