The World Health Organization raised its pandemic alert to phase six, formally declaring that the H1N1 influenza strain first identified in Mexico had become a pandemic.
Officials stressed that the severity of most cases remained moderate, but said sustained community transmission on more than one continent met the technical threshold for a pandemic. Health ministries were urged to prepare surveillance, antiviral stockpiles and hospital surge capacity.
Vaccine production began within months, though supply was heavily concentrated in wealthy countries, an imbalance that later shaped debate over equitable access during subsequent health emergencies.
