Vaccine hesitancy refers to a delay in acceptance, or refusal of vaccines despite the availability of vaccine services. Vaccine hesitancy is complex and context specific, varying across time, place and vaccines. It is influenced by factors such as complacency, convenience and confidence. The term covers outright refusals to vaccinate, delaying vaccines, accepting vaccines but remaining uncertain about their use, or using certain vaccines but not others. Among the hesitant are groups known as "anti-vaxxers" or "anti vax", who are generally against vaccination.