How many major viruses have their been in history?

Throughout history, there have been several major viruses that have significantly impacted human populations. Notable examples include the influenza virus, HIV, smallpox, and more recently, the coronaviruses SARS-CoV and SARS-CoV-2 (responsible for COVID-19). While it's challenging to quantify precisely how many "major" viruses there are, public health organizations often focus on a few dozen that have caused widespread outbreaks or pandemics. The list continues to evolve as new viruses emerge and are studied.