Measles remains an important cause of childhood mortality, and global eradication of the disease is being seriously considered. Because of limitations of the current live-attenuated vaccines, new vaccines and routes of administration are being investigated. In the article under review, the authors have measured measles-specific humoral and cellular immune responses after two doses of live-attenuated measles vaccine and found limited correlation between the two. This study highlights an important issue, namely that we cannot assume humoral and cellular immune responses to go hand in hand. However, it remains to be determined if assays with peripheral blood lymphocytes can be used as a correlate of protection from disease.