Merck & Co.’s blockbuster vaccine Gardasil has had a roller-coaster ride in China. A post-Covid surge in demand for the cancer-preventing shot quickly deflated last year, to the point the US pharmaceutical giant made the call earlier this week to halt shipments.

Shares of Merck are sliding in early trading after the drugmaker surprised Wall Street with a lower-than-expected 2025 sales forecast due partly to a pause in shipments of one of its top-selling products to China.