Epidemic: The occurrence of an illness/ health condition in a given area that is clearly in excess of expected frequency.
In simple words, when a health condition/ illness occurs in much greater numbers than usual (expected frequency), it is termed an epidemic.
Pandemic: An epidemic occurring over a very wide area, crossing international boundaries, and usually affecting a large number of people.
In simple words, a pandemic is an epidemic that involves multiple countries/ geographical regions and affects a large number of people. Here, the geographical spread is key, not necessarily the severity of the disease (as evidenced by number of deaths/ serious illness, for instance).
The presence of a pandemic is determined and declared by the World Health Organization (WHO) under International Health Regulations (IHR).
Pandemic risk is driven by the combined effects of
- spark risk (where a pandemic is likely to arise) and
- spread risk (how likely it is to diffuse broadly through human populations)
Most new pandemics have occurred due to animal-human interaction resulting in zoonotic transmission of disease agent(s) from animals to humans.
A zoonotic spark could arise from the introduction of a pathogen from either domesticated animals or wildlife. Zoonoses from domesticated animals are concentrated in areas with dense livestock production systems, including areas of China, India, Japan, the United States, and Western Europe. Wildlife zoonosis risk is distributed far more broadly, with foci in China, India, West and Central Africa, and the Amazon Basin.
After a spark or importation, the risk that a pathogen will spread within a population is influenced by
- pathogen specific factors including genetic adaptation; mode of transmission, and
- human population-level factors such as
- the density of the population and the susceptibility to infection;
- patterns of movement driven by travel, trade, and migration; and
- speed and effectiveness of public health surveillance and response measures
Situational awareness—in the context of pandemic preparedness—can be defined as having an accurate, up-to-date view of potential or ongoing infectious disease threats (including through traditional surveillance in humans and animals) and the resources (human, financial, informational, and institutional) available to manage those threats.
Situational awareness supports policy decisions by tracking if and where disease transmission is occurring, detecting the most effective methods to reduce transmissibility, and deciding where to allocate resources. During a pandemic, situational awareness allows for monitoring to understand the course a pandemic is taking and whether intervention measures are effective.