The Centers for Disease Control and Prevention has told clinicians, health departments, and the public that a widely used class of immune medications can raise the risk that an ordinary mosquito or tick bite becomes a severe brain infection. The agency issued the notice on August 11, 2026, through its Health Alert Network advisory system as CDCHAN-00532, and it names the drugs directly.
The medications are B-cell-depleting and B-cell-modulating agents, led by monoclonal antibodies that target the CD20 protein. The advisory lists rituximab and its biosimilars, ocrelizumab, ofatumumab, ublituximab, obinutuzumab, and ibritumomab tiuxetan as the anti-CD20 antibodies currently approved in the United States. Drugs in this broader class are prescribed for B-cell cancers, for many autoimmune conditions, and for transplant rejection.
