Here's why store shelves are empty again in parts of the U.S.

The recent spread of the omicron variant among supply chain workers, sour weather and even a recall of bagged salads and vegetables have caused Americans to once again find barren shelves at supermarkets or retail stores. 

While industry leaders hope this latest supply chain foul-up will be a short-term frustration, it comes amid the ongoing challenges they’ve faced during the pandemic: shipping delays, congestion at ports, labor shortages and more. 

Doug Baker, vice president of industry relations for the Food Marketing Institute, a trade group, said the latest Covid-19 variant and the bad stretch...