This invention concerns improved single use caps or covers for vascular access devices such as needlefree connectors that are used, for example, in intravenous administration sets and extension sets. Removal of a single use cap or cover according to the invention from a vascular access device destroys the cap such that the cap cannot be reused. Said single use caps or covers will help ensure compliance with infection prevention protocols in healthcare settings, which will assist in reducing incidences of healthcare-associated infections (HAIs), particularly catheter-related blood stream infections. Assemblies and kits including said caps or covers, for example, IV administration and extension sets that include one or more needlefree connectors, as well as methods for using said caps or covers, are also described.