Keiji Fukuda, WHO assistant director-general, announced the agency's updated figures at a two-day summit on influenza being held in the Mexican resort city of Cancun.
Fukuda said most of the cases were of young people with prior health problems, but he warned that the future of the disease remained uncertain, including its severity, clinical patterns and the structure of the virus.
He said "flexibility" was vital as the international health community prepares for the evolution of the pandemic.
Deccan Herald is on WhatsApp Channels | Join now for Breaking News & Editor's Picks