Final answer:
Influenza A virus has a greater risk of causing pandemics than influenza B because it is more virulent, has a wider host range, and the potential for antigenic shifts, leading to new strains against which humans have no immunity.
Step-by-step explanation:
Influenza A virus poses a greater risk of pandemics compared to influenza B virus for several reasons. The influenza A virus is more virulent and has a wider host range, infecting various animals, which may serve as reservoirs for the virus. This increases the potential for antigenic shifts, where the virus acquires new genetic material, potentially leading to the emergence of a novel strain to which the human population has little to no immunity. This is less likely to occur with influenza B virus, which has a more limited impact due to its absence of significant animal reservoirs and tends to cause less severe outbreaks.
The potential for pandemics is further exacerbated because the influenza A virus can undergo both antigenic drift and shift. Antigenic drift involves minor changes, while antigenic shift can result in a major change due to the reassortment of viral genes. Dramatic changes in the hemagglutinin and neuraminidase proteins of the virus could result in new subtypes against which the human population has not developed immunity, leading to widespread illness and increased mortality rates.
Historically, significant pandemics, including those in the 20th century, have been caused by novel strains of the influenza A virus. Agencies such as the World Health Organization and the Centers for Disease Control and Prevention monitor influenza outbreaks closely due to the persistent threat posed by the potential for antigenic shift in the influenza A virus, which could result in a pandemic with a high mortality rate, as illustrated by historical pandemics and recent outbreaks.