Epidemics of infectious diseases are occurring more often, and spreading faster and further than ever, in many different regions of the world. The background factors of this threat are biological, environmental and lifestyle changes, among others.

A potentially fatal combination of newly-discovered diseases, and the re-emergence of many long-established ones, demands urgent responses in all countries. Planning and preparation for epidemic prevention and control are essential.

These diseases have been selected because they represent potential international threats for which immediate responses are critical. Nearly all of them are subject to WHO’s International Health Regulations (2005) monitoring and are part of the Global Health Security Agenda.

Perhaps the greatest threat outlined in the manual is an influenza pandemic, which is both unpredictable and inevitable. In the worst-case scenario, there will be no protective vaccine for six months or longer after the virus is identified, and even there will be a global shortage of doses.