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Researchers are constantly working to develop new vaccines and improve old vaccines. One of the chief motivating factors is reducing the rate of illness in the developing world. The use of live vaccines, which are among the most effective for many diseases, is often impractical in places where refrigeration is not possible. The production of inexpensive and practical vaccines for use in developing countries is key to eliminating many of the diseases that are prevalent in those parts of the world. Scientists are working on various vaccine alternatives, including:

• Edible vaccines. Scientists are in the process of developing a type of vaccine that can be administered by eating genetically engineered fruit and vegetables. For example, potatoes have been genetically engineered to produce a response against E. coli antigens and bananas are being developed to protect against Norwalk virus, which is a common cause of diarrhea.
  
  
• Skin patch vaccines. Vaccines that could be administered through a skin patch are currently being tested in both laboratory mice and humans. Antibody response to the bacteria E. coli, for example, has been observed in humans who used a skin patch vaccine.
  
  
• Nasal spray vaccines. A nasal spray to replace the flu vaccine was recently approved by the Food and Drug Administration for use in people aged 5 to 49 who are not pregnant. This live vaccine is thought to be more effective than the traditional flu shot because it replicates the way in which the flu virus enters the body – through the respiratory system – therefore producing a better immune response. It is thought that this method of vaccination could be used for other diseases.