In 1918 flu pandemic, not wearing a mask was illegal in some parts of US. What changed?

When the novel coronavirus pandemic hit Asia, people across the region were quick to wear masks, with some places like Taiwan and the Philippines even making them mandatory in certain scenarios.

from CNN.com - RSS Channel - App International Edition https://www.cnn.com/2020/04/03/americas/flu-america-1918-masks-intl-hnk/index.html
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