Final answer:
At the end of a pandemic, a virus that can only live in humans would decline as the population builds immunity, potentially leading to its extinction unless it evolves or finds new susceptible hosts.
However, the interconnectedness and urbanization of the global population means that the threat of new pandemics continues, as new viruses emerge and spread.
Step-by-step explanation:
If a virus can only live in humans, at the end of a pandemic, the virus would typically decline in presence. This decline happens because of increased immunity in the population, either through recovery from infection or via vaccination. With fewer susceptible hosts, the virus loses its ability to spread effectively.
However, if the virus cannot find new hosts, it faces the risk of extinction. Viruses depend on a contiguous population to maintain their existence. For example, the measles virus requires a population of around 300,000 to sustain itself.
Once global herd immunity is achieved, or the population drops below the required threshold, the chain of transmission is broken, leading to a die-out of the virus, at least until another susceptible population emerges.
The global population however, is now highly interconnected and urbanized, which provides a fertile ground for new viruses to emerge and spread, creating a cycle where new strains have the potential to spark fresh outbreaks.
Therefore, modern pandemics can be mitigated through international cooperation, surveillance, quick response systems, and medical advances like vaccination programs.
Still, the threat of new pandemics remains, as evidenced by recent outbreaks of influenza strains and the COVID-19 pandemic.