Influenza vaccination increases anti-JC virus antibody levels during treatment with Natalizumab: Case report.

Background: Natalizumab (NTZ) is an effective therapy for multiple sclerosis (MS). A common concern related to NTZ therapy is the risk of developing progressive multifocal leukoencephalopathy (PML).

Clinical Case: A patient that after seven years on NTZ therapy, testing on every 3 months repeated evaluations negative for anti-JCV status became positive (>3 units) 4 weeks after receiving influenza vaccine. Despite continuous therapy on NTZ for additional 2 years her anti-JCV index progressively declined to a level 0.6 units

Conclusion: Our case raises the consideration to include vaccination as a factor that can affect JCV index and should be tallied during NTZ treatment mitigation.