Intranasal DNA Vaccine for Protection against Respiratory Infectious Diseases: The Delivery Perspectives

Xu, Yingying; Yuen, Pak-Wai; Lam, Jenny Ka-Wing

To evaluate the efficacy of DNA vaccine in humans, serum antibody titer or the enzyme-linked immunoSpot (ELISpot) assays are the commonly employed methods to measure the immunogenic response, although the induction of antigen-specific immune effectors by an immunization process does not imply that these antibodies or cytokines represent surrogates or correlates of vaccine efficacy. In early stage of vaccine development, in vitro serum antibodies and ELISpot assays are the direct detectable indicators of the clinical potential of a vaccine formulation. At later stage of development, morbidity and mortality (especially the improvement of survival rate after vaccination) in animals upon target pathogen challenge is a more certain way to confirm the protective efficacy of vaccines [28, 29] , as the ultimate goal of vaccine is to prevent the targeted disease. The efficacy of vaccine such as influenza vaccine could be monitored in human during subsequent influenza epidemic season [30, 31] or challenged with a controlled influenza virus [32] . However, some lethal virus challenge studies are difficult to conduct directly on human. Hence, the measurement of antibodies production and immune responses in humans remain the most direct way to assess vaccine efficacy. Longer study is required to investigate if the vaccine is indeed able to prevent disease.