In the WHO pandemic phases, which phase indicates efficient/sustained human-to-human transmission?

• A. Phase 6: Efficient/sustained human-to-human transmission is occurring
• B. Phase 1: Low risk of cases in humans
• C. Phase 3: Human-to-human transmission is nonexistent to low
• D. Phase 5: Significant human-to-human transmission is occurring

Answer: (A)

Think about how the WHO tracks the spread of a virus from initial spillover to global impact. Efficient and sustained human-to-human transmission means the virus can spread easily between people and keep doing so across many places over time, not just in scattered cases or small clusters. That level of spread is reached in the pandemic phase, when transmission is increased and continues across multiple regions worldwide. Earlier stages describe limited transmission, small clusters, or outbreaks in a few areas, but not the global, ongoing spread that defines a pandemic.