evidence: "Factors that may decrease vaccine response among immunocompromised populations include older age, primary immune deficiency, lower lymphocyte counts, decreased kidney function, being on immunosuppressive drugs or high dose corticosteroids and current or recent cancer treatment," she said. "For example, a study looking at mRNA vaccine effectiveness in immunocompromised populations found 59–71% effectiveness against infection for immunocompromised people versus 90–94% overall.