Adenovirus-based
vaccines are demonstrating promising clinical potential for multiple
infectious diseases, including
COVID-19. However, the immunogenicity of the vector itself decreases its effectiveness as a boosting
vaccine due to the induction of strong anti-vector neutralizing immunity. Here we determined how dissolvable microneedle patches (DMN) for skin immunization can overcome this issue, using a clinically-relevant adenovirus-based
Plasmodium falciparum malaria vaccine, AdHu5-PfRH5, in mice. Incorporation of
vaccine into patches significantly enhanced its thermostability compared to the liquid form. Conventional high dose repeated immunization by the intramuscular (IM) route induced low
antigen-specific
IgG titres and high anti-vector immunity. A low priming dose of
vaccine, by the IM route, but more so using DMN patches, induced the most efficacious immune responses, assessed by parasite growth inhibitory activity (GIA) assays. Administration of low dose AdHu5-PfRH5 using patches to the skin, boosted by high dose IM, induced the highest
antigen-specific serum
IgG response after boosting, the greatest skewing of the antibody response towards the
antigen and away from the vector, and the highest efficacy. This study therefore demonstrates that repeated use of the same
adenovirus vaccine can be highly immunogenic towards the transgene if a low dose is used to prime the response. It also provides a method of stabilizing
adenovirus vaccine, in easy-to-administer dissolvable microneedle patches, permitting storage and distribution out of cold chain.