Why does influenza A virus pose a greater risk of pandemics compared to influenza B?

The influenza A virus poses a greater risk of pandemics primarily because it resides in natural animal reservoirs, particularly in birds and other animals, which can facilitate the transmission of the virus among different species. This zoonotic potential is significant, as it allows influenza A to acquire new genetic material through reassortment, especially when it infects different species. This process can lead to the emergence of novel strains to which the human population has little or no immunity, thus increasing the likelihood of widespread outbreaks or pandemics.

On the other hand, influenza B is primarily associated with humans and does not exhibit the same level of genetic diversity or capacity for reassortment as influenza A. Additionally, influenza B typically has a more stable evolutionary pattern and does not pose the same level of threat for cross-species transmission.

While other options touch on aspects of influenza and its impact, the presence of influenza A in diverse animal reservoirs gives it a distinct advantage in terms of pandemic potential due to the opportunity for the virus to mutate and easily spread to humans, thereby leading to outbreaks on a global scale.