No vaccine currently exists to protect against infection with the sexually transmitted bacterium Chlamydia trachomatis, which can cause female infertility and ectopic pregnancies and is the leading cause of preventable blindness in developing countries. Now, however, investigators at Harvard Medical School, in Boston, present a promising candidate vaccine consisting of UV light–inactivated C trachomatis tightly conjugated to charged nanoparticles carrying an adjuvant to boost the immune response (Stary G et al. Science. 2015;348[6241]:aaa8205).