The protective measures have not only helped to
keep this virus in check but also have driven down
cases of regular flu and “has”reduced case of stomach flu by 90%
請問為什麼” “內不是have? 而是has

看了也充滿疑惑，求解，想知道是不是筆誤！

看起來是筆誤

這段除了原PO說的地方之外還有其他的錯誤，看得懂就好，遇到這種句子不用太糾結，很多外媒的文章與撰文者寫作功力都很參差不齊的～