The development of a needle-free vaccination delivery system has been identified by the Grand Challenges in Global Health (GCGH) initiative as one of the major challenges facing global health care today.
Millions of needles and syringes are used each day in health care. The World Health Organization (WHO) estimates that 12 billion injections are given each year. Only about 5% are used in the delivery of vaccines for immunization and prevention of infectious diseases. Even though vaccinations have saved lives over the years, there are some hurdles to overcome. One of these is the use of needles or “sharps” to deliver the vaccines.
According to Myron Levine of the Center for Vaccine Development, University of Maryland School of Medicine and member of the Global Alliance for Vaccines and Immunization (GAVI) “three fundamental themes remain in common worldwide: first, high immunization coverage of target populations generally must be attained for maximal public health impact; second, most current vaccines are administered parenterally using a needle and syringe; third, there is a broad recognition of the need to find ways to administer vaccines without the use of ‘sharps’ (that is, needles and syringes).”
The disadvantages of needle delivery of vaccine include:
(1) Pain and irritation of vaccination site. A large fraction of our population is scared of needles, probably as consequence of a previous bad experience. The majority of patients at the delivery end of vaccination are very young children under the age of two and needle pricks in this patient population can cause a lot of pain and distress. Needles may also cause discomfort at the injection site long after the shot has been applied.
(2) Lack of compliance. The World Health Organization’s Expanded Programme on Immunization (EPI) has recommended six basic vaccines for infants in developing countries: diphtheria, pertussis, and tetanus toxoids (DPT), bacillus Calmette-Guerin (BCG), and attenuated polio and measles. In developed countries such as the US, more vaccinations are required by health authorities. However, for the so-called “herd immunity” to work, a certain % of the population must comply with vaccination schedule.
(3) Safety. Vaccination with needles produces dangerous infectious waste that come with serious health threats to both patient and health care professionals. The reuse of unsterilized needles has facilitated the transmission of blood-borne infections such as HIV and hepatitis.
(4) Speed and efficiency. Recently, the threats of bioterrorism and pandemic flu have highlighted the need of fast, easy and safe vaccine delivery to the masses should the need arise. Definitely, vaccination using syringes and needles was not designed for these situations.
(5) Cost-efficiency and logistics. Doing away with syringes and needles can make vaccinations in less developed countries cheaper and more accessible. Syringes and needles need to be transported and stored for vaccination purposes. Injectible vaccines need to be refrigerated during transport.
Although needle-free delivery systems exist for many drugs, vaccines present a challenge because they usually consist of large molecules that cannot be easily delivered transdermally. Myron Levine summarized in a review article the different methods of administrating needle-free vaccines.
(1) Vaccines delivered through mucosal surfaces. Though theoretically possible, this form of delivery hasn’t caught on except perhaps with the use of the nasal spray.
(2) Oral vaccines. Specific vaccines can be given orally in the form of pills. Oral polio vaccine has already been around for awhile. Other vaccines can be delivered via this route including certain types of cholera vaccines and the new rotavirus vaccines. However, this delivery route presents some problems for very young infants who might not be able to swallow properly and whose digestive system may not be able to withstand the effects of the vaccines.
(3) Nasal vaccines. The nasal vaccine through the respiratory tract is a very popular alternative to the flu shot. The FluMist” nasal spray, made from live, attenuated, cold-adapted vaccine, has been approved by the FDA and is delivered using a single-use spraying device through the nostrils.
(4) Aerosol vaccine. This mode of administration through the respiratory tract has been tested for measles vaccine. This is an alternative to the nasal spray and can be used with liquid aerosol and dry power for mass immunization.
(5) Needle-free percutaneous jet injection. This device works by propelling liquid through a small skin pore under high pressure. The liquid is then transported to the dermis and underlying tissues and muscles. There are multiple dose injectors available, making this type of delivery fast and practical for mass immunizations. However, it has the disadvantage of a high incidence of local irritation at the vaccination site as well as the possibility of transmission of infectious diseases.
(6) Transcutaneous delivery. This is commonly known as the “vaccine patch” and is delivered via the skin. The adhesive patch is applied after a preliminary hydration, directly on the skin. The occlusive patch makes the skin permeable to the vaccine. The cutaneously applied antigens are then taken up by Langerhans cells found in the upper layer (epidermis) of the skin allowing the immune-processing cells to migrate to the lymph nodes.
