The phrase "serious damage" refers to significant harm or injury that has been caused to something or someone. It means there has been a severe negative impact or destruction on a particular object, person, or situation. Full definition
Even when they're just screening they can do serious damage by filtering out great resumes. (careerdigital.com)
Climate change is unlikely to be catastrophic in the near term, but it has the potential for serious damages in the long run. (dotearth.blogs.nytimes.com)