Why the world is still arguing over face masks, 20 months into the pandemic

The science behind masks is clear. Yet debates still rage in multiple countries over their use, and some regions have recently removed mandates that people wear them in crowded spaces.

Spikes in transmission were met with lockdowns; international travel was heavily restricted; and though domestic constraints frequently proved controversial, hygiene measures like social distancing, hand-washing and mask-wearing were strongly encouraged -- if not legally mandated.

But those days are behind us. Pandemic management now differs widely from country to country -- with the face mask just one example of the world's increasingly fractured approach to Covid-19.