I was in SE Asia when H1N1pdm9 hit. There were 60m cases in the US that year, and 14,000 deaths that year in the US, and 75,000 deaths since 2009. It predominantly affected younger people[1], and barely hit elderly people. The CDC estimates it killed 150k to 500k people the first year it circulated across the world. I was wearing a mask in Macau, and my kids aged 12 and 9 years-old in the US at the time were not as almost all Americans were not wearing masks. The WHO declared an end to the pandemic in August 2010, but it causes illness, hospitalizations, and deaths each year as a seasonal flu the same way COVID-19 probably will in the coming years.

[1] https://www.cdc.gov/flu/pandemic-resources/2009-h1n1-pandemi...