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Promising new technologies from recombinant DNA and biodegradable polymer research will change the way vaccines are produced and will simplify how immunity is induced and maintained (Michalek et al., 1995; Walker, 1994). Two recent papers demonstrate the feasibility of large-scale agricultural production of recombinant vaccine antigens (Ma et al., 1995) and functional recombinant human antibodies (Haq et al., 1995) in quantities that would satisfy virtually any contingency requirement. Engineered human secretory antibodies could be enterically coated and incorporated into foods for passive protection of soldiers from common diarrheal diseases and enterotoxin reactions that affect nutrition and performance (Hyams et al., 1991, 1993; Sarraf et al., 1997).

The advantages of passive and active immunization2 via the oral route are multiple. Recombinant vaccines may be encapsulated in biodegradable polymers to prolong shelf life and provide controlled-release, targeted delivery or protection from denaturation by stomach acid and intestinal enzymes until the product is absorbed in the gastrointestinal tract (Michalek et al., 1994; Morris et al., 1994). Combining encapsulated vaccines or antibodies with nutritious foods makes them more convenient and acceptable to use and removes the logistical and anxiety factors associated with the need for periodic inoculations. In addition to enhancing soldier performance and autonomy, systems for oral immunization will save time and money. It will no longer be necessary for soldiers to delay deployment so that they may assemble for vaccination. Because the new vaccines can be self-administered, they can be taken without need of medically trained personnel. Oral vaccination also eliminates dangerous medical waste and the risk of contamination, which are concerns when needles are used. Taken together, it is now feasible to provide complete passive and active protective immunity along with good nutrition in Meals, Ready-to-Eat (MREs). These new technologies should become an exciting and active area of applied research with

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Passive immunity is an unsustainable state of immunity produced by transfer of antibodies from an immunized donor (after convalescence or complete immunization regimen) to a nonimmune recipient. Protection may be sustained only if regular treatments of antibody are given. In other words, antibody from an immune donor is put into a nonimmune recipient, thus conferring a state of immunity. In this review, passive immunity is used to indicate the prevention or reduction of ''traveler's diarrhea" or infections that affect soldiers within the first few days of deployment.

Active immunity is a sustainable state of immunity that results from vaccinations or recovery from an infectious illness. This kind of immunity is antigen specific and can result in logarithmically increasing amounts of antibody and other forms of immunity upon re-exposure to antigen. The most important aspect of active immunity is that immunological memory is induced. Immunological memory results from clonal expansion of lymphocytes specific for the antigen during the primary response. These lymphocytes reside in lymphatic tissues and circulate in the blood. After immunization, there may be many thousands of antigen-specific lymphocytes circulating or residing in tissues. Upon re-exposure to antigen, the rate and magnitude of the specific secondary immune response is orders of magnitude greater than the primary response. Immunological memory resulting from active immunization is more valuable for protecting soldiers than is passive immunity.



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