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FAQ
What was the deadliest pandemic in history?
The Black Death 1347 to 1351 killed an estimated 75 to 200 million people, potentially half the population of Europe. The 1918 Spanish Flu killed an estimated 17 to 50 million, possibly more. Smallpox killed an estimated 300 million people in the 20th century alone before its eradication was certified in 1980.
What is a PHEIC?
A Public Health Emergency of International Concern is a formal WHO alert under the International Health Regulations; since September 2025 a higher pandemic emergency level also exists. It lets the WHO issue temporary recommendations, which are non-binding, while the IHR themselves are legally binding. The WHO has declared 9 PHEICs since 2009, including COVID 19, Ebola, Zika, and mpox, most recently for Bundibugyo Ebola in May 2026.
What is R0?
The basic reproduction number R0 is the average number of people one infected person infects in a susceptible population. Measles has the highest R0 at 12 to 18. The original COVID 19 strain was estimated at roughly 2 to 3, with later variants such as Omicron considerably higher.
What is herd immunity?
Herd immunity occurs when enough people are immune to stop transmission. The threshold depends on R0. For measles it is 95 percent. For the original COVID 19 strain it was estimated at around two thirds, and more transmissible variants pushed estimates higher.
How are vaccines developed so quickly?
COVID vaccines used mRNA technology developed over 30 years. Massive government funding through Operation Warp Speed enabled parallel manufacturing. Regulatory agencies used emergency authorization pathways. No safety steps were skipped.
What is Disease X?
Disease X is the WHO designation for an unknown pathogen that could cause a future pandemic. Preparedness for Disease X requires flexible platform technologies, surveillance systems, and response capabilities that can be adapted to any pathogen.