During the pandemic, fake news has been proliferating rapidly, which is concerning.

proliferating 是动词 proliferate 的现在分词形式。proliferate 由前缀 pro-（表示"向前"）和拉丁词根 ferre（意为"携带"）组成，字面意思是"向前携带"，引申为"快速繁殖、扩散"的意思。在这里指谣言像生物繁殖一样快速传播扩散。