WASHINGTON, D.C. - The current recommended childhood immunization schedule requires a minimum of 14 injections of vaccine for children and young adults up to age 16. To accommodate future vaccines in development, the Centers for Disease Control and Prevention (CDC) is exploring alternative methods to using a needle and syringe for immunizations.
Bruce G. Weniger, MD, MPH, assistant chief for Vaccine Development, Vaccine Safety and Development Activity at the CDC's National Immunization Program, said future vaccination technologies include aerosol vaccines delivered as nose spray, immunization through skin contact, eating plants that contain vaccines and new oral vaccines.
In 1989, the recommended immunization schedule required basically eight injections, plus the oral polio vaccine. The 1998 recommended schedule requires a minimum of 14 injections, and in some cases up to four injections are received in the same visit.
Various surveys indicated between 21% to 60% of physicians and parents object to giving three injections and even higher percentages object to giving four injections. The visits are then deferred, the parents are forced to take off more time from work, or they don't come back and the child remains unprotected.
In the last 15 to 18 years, four new diseases (hepatitis B, Haemophilus influenzae type b, varicella and hepatitis A) have become vaccine preventable. In the next few years, new vaccines for rotavirus, Lyme disease, respiratory syncytial virus, Pneumococcus and Meningococcus will likely be available. However, the news is not all good.
"The problem is, it will be difficult to incorporate these future vaccines into our immunization programs," Weniger said at a recent National Foundation for Infectious Diseases press conference and symposium on infectious diseases.
A traditional solution to excessive injections to is to combine separate vaccines into the same vial or syringe. Weniger mentioned the combined diphtheria-tetanus-pertussis and measles-mumps-rubella vaccines, and added that vaccine combinations against up to seven diseases may eventually be available.
"The problem is that these vaccines are very difficult and expensive to produce. Every time you add a new vaccine to the mix, you have to start all over again and prove that the new product is safe and will continue to be effective in preventing disease in the child," he said. "There have been problems overcoming chemical incompatibility or immunological interference."
Another alternative is to do away with the needle, Weniger said. Fifty years ago, needle-free injection devices were developed that squirted a high-pressure, fine-stream of vaccines through the skin into the soft tissue and muscle.
The devices were initially used to curb the fear of children with diabetes who had to take daily insulin injections. Since then, dozens of such devices have been developed, and high-speed devices have been used during mass immunization campaigns.
"Some of the previous devices have raised concerns over safety because they used the same nozzle tip to vaccinate different patients, and the fear is that microscopic amounts of blood might be transferred from patient to patient," Weniger said. "So, we [CDC] are working with industry to develop a new generation of devices that will use completely disposable nozzles."
One such device, Biojector 2000, is already approved for use in the United States and is used in a number of immunization clinics around the country, he added.
Although needle phobia is reduced, these devices are not yet entirely pain-free. The use of a multichannel injector is also being explored: "If we cannot reduce the pain, can we reduce the number of separate injections? Can we deliver them in one simultaneous injection, having only a single painful event?" Weniger said.
Oral or nasal vaccines are the obvious ideal solution, Weniger said. In addition to the oral polio vaccine already being used, Food and Drug Administration licensure of the oral rotavirus vaccine (RotaShield, Wyeth-Lederle) is expected at any time.
DNA vaccines are different than traditional vaccines. They provide the blueprints of the organism and let the body's cells manufacture the components that stimulate the immune response.
Another option for minimizing injections is to genetically engineer oral vaccines to protect against additional diseases. Live Salmonella typhi vaccine has been engineered experimentally to carry antigens for Shigella, Escherichia coli and malaria, he said.
Using plants for immunizations is another area of interest. Through genetic engineering, plants can now synthesize the vaccine. Potential plants include corn, potato, tobacco, tomato, alfalfa, lettuce and spinach. An advantage of this technology is the small expense involved with producing the vaccine, which would be extremely beneficial in the developing world.
"This technology offers the possibility of a relatively low cost of manufacturing," Weniger said. "I'm a little more skeptical about the possibility of going to the doctor's office where the child will be handed a banana or brussel sprout or whatever, and be immunized by eating that fruit or vegetable. The shelf life of fresh vegetables is not very long and it's not practical to ship vegetables around the country.
"In addition, too much of a good thing may not be so good. Vaccine dosages have to be controlled; too much of a vaccine can have side effects," he said.
Weniger suggested the more likely possibility is that manufacturers will use the plant to synthesize the vaccine, which will extracted in traditional packaging such as drops, injections or pills.
The use of adjuvants is the latest exciting area in immunizations.. These additional chemicals added to the vaccine make it work better. A recent example of this is being used to develop a promising malaria vaccine.
Encapsulating various vaccines in protective shells or coatings is yet another alternative method for immunization delivery. Some vaccines now injected may be able to be delivered orally if these shells can protect them from the acid in the stomach.
You can express your views on this article, or other relevant themes, in the Infectious Diseases in Children Specialty Forums.