CD4 and chronic hepatitis C virus infection: To prevent viral persistence effectively, strong T cell responses including CD4+ and CD8+ T cells and prolonged memory T cell response against HCV are considered as necessary because sterilizing immunity is not protective in chronic hepatitis C. For human use, recombinant viral vaccines, such as the MVA construct above, require careful assessment for adverse events; they are limited in use in pregnancy and cannot be used in immunosuppressed individuals due to the possibility of disseminated infection.