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A pandemic (from the Greek pan, “all,” and demos, “people”) is the worldwide spread of a previously unknown disease. Steps toward a pandemic include outbreaks (the emergence of a disease in a specific city or country) and epidemics (a rise in infections that’s dramatically or suddenly higher than what’s expected). But definitions vary among health agencies about what “worldwide” means, so a disease may reach lots of countries but not be called a pandemic. The last generally agreed-upon pandemic was in 2009, when a new flu strain called H1N1 emerged.

Pandemics don’t make diseases any deadlier per se; for instance, you could have a pandemic of a virus with a zero-per-cent mortality rate in which lots of people get sick but no one is killed. But when potentially fatal diseases such as COVID-19 reach pandemic status, they get harder to predict and fight, meaning the most at-risk groups are likelier to be infected.

  • Learn more here about how pandemics are defined and how Canadian health officials are trained to respond to them.

You can also check The Globe and Mail’s digest of the latest news about COVID-19′s spread around the world.