Definition According to the ORGANIZATION@1 -LRB- WHO -RRB- , a pandemic can start when three conditions have been met : emergence of a disease new to a population ; agents infect humans , causing serious illness ; and agents spread easily and sustainably among humans .

Common killers and pandemics According to the ORGANIZATION@1 , a pandemic can start when three conditions have been met : the emergence of a disease new to the population .
