Immunization without needles

Key Points Needles and syringes are the most commonly used method for administering vaccines. They are responsible for numerous cases of transmission of HIV, hepatitis B virus and hepatitis C virus, which have arisen from the reuse of needles and syringes. Development of needle-free methods of immunization is a high priority. Current options for needle-free immunization can be classified into four categories: liquid-jet injection, epidermal powder immunization, and topical application (which are all types of cutaneous immunization), and mucosal immunization. Liquid-jet injection has been used for immunization for more than 50 years. Multi-use-nozzle jet injectors have been used for mass immunization, but this practice was discontinued because of concerns about cross-contamination. At present, disposable-cartridge jet injectors are used for immunization in clinics. Epidermal powder immunization delivers dry particulate vaccine to the epidermis. It effectively targets Langerhans cells. Topical vaccine application is being developed for immunization. Various methods — including topical adjuvant patches, colloidal carriers, and physical methods, such as ultrasound, microneedles, tape stripping and thermal microporation — are being used to improve vaccine penetration of the skin and to provide adjuvant activity. During mucosal immunization, vaccines are delivered through the ocular, oral, nasal, pulmonary, vaginal or rectal route. Various methods — including the use of adjuvants (such as the cholera toxin B subunit and bacterial ghosts) and the encapsulation of vaccines in carriers (such as liposomes and microspheres) — are being developed for mucosal immunization. In the past decade, considerable progress has been made towards needle-free immunization. At present, several companies are developing needle-free methods of immunization. Most current immunization procedures make use of needles and syringes for vaccine administration. With the increase in the number of immunizations that children around the world routinely receive, health organizations are beginning to look for safer alternatives that reduce the risk of cross-contamination that arises from needle reuse. This article focuses on contemporary developments in needle-free methods of immunization, such as liquid-jet injectors, topical application to the skin, oral pills and nasal sprays.