Vaccines have curtailed the spread of several infectious diseases, such as smallpox, polio and measles. However, vaccines against some diseases, including HIV-1, influenza and malaria, don’t work very well, and one reason could be the timing of antigen and adjuvant presentation to the immune system. Now, researchers have developed an injectable hydrogel that allows sustained release of vaccine components, increasing the potency, quality and duration of immune responses in mice.