Nigeria, Sept. 29 -- The pandemic has reached a grim milestone: one million people have now died of COVID-19, according to Worldometers.

On January 13, we published "Mystery China pneumonia outbreak likely caused by new human coronavirus" by Connor Bamford, a virologist at Queen's University Belfast. Since then, we have published more than 3,500 articles on the now not-so-novel coronavirus, officially named Sars-CoV-2. Despite this huge output from the world's leading experts, we have merely skimmed the surface of all there is to know about this perplexing pathogen. So much remains a mystery.

At this important juncture, we asked several experts from different fields what their burning question about the coronavirus is. Here is what they...