4.2 What COVID-19 cost, and why worse is possible

That is equivalent to more than four in five people living in the Netherlands. On top of the deaths came lost schooling, lost income and years of disruption.

As pathogens go, COVID-19 was not the worst nature could produce. Most people who caught it survived. A virus that spread as easily and killed a much larger share of the people it infected would be a different kind of event.

A further risk comes from human design rather than nature. Biotechnology keeps getting cheaper and more widely available. That is mostly good news: it gave us mRNA vaccines within a year. But the same tools could be used to make pathogens more dangerous, by accident or on purpose. The International AI Safety Report 2026, written by over 100 experts from more than 30 countries, notes that advances in AI's scientific abilities have "heightened concerns about misuse in biological weapons development".

This course stays at that level of detail on purpose. Specifics about how such harm could be caused are hazardous to spread, and you don't need them to understand the problem.