It's all about delivery Human immunodeficiency virus (HIV) has proved to be a notoriously difficult virus to vaccinate against. Most immunization studies focus on altering components of the vaccine to improve immune responses. Cirelli et al. instead asked what would happen if they changed the delivery method rather than vaccine composition. Slow vaccine delivery-in small amounts over several days-was found to enhance HIV neutralizing antibodies when compared with standard methods where the vaccine is injected all at once. Rhesus monkeys developed more potent T follicular helper cell responses, and germinal center B cells showed improved SCIENCE sciencemag.org