Vaccines

Vaccines are predominantly used for prevention; that means they should establish a protection in immunized people or animals which will protect them from a possible infection and the subsequent illness when they come into contact with the respective pathogens. Fundamentally, there are two kinds of immunization: active and passive. The latter is based on the administration of immunoglobulin preparations that can neutralize a specific virus. Therefore, passive vaccination is applied only in special cases, such as when the person to be protected recently had verifiable contact with a specific virus (postexposure prophylaxis), or if the risk of exposure to pathogens cannot be ruled out in the following weeks and an active vaccination is not possible, as in short-term planned trips to Third World countries (exposure prophylaxis). An example is the administration of antibodies specific for hepatitis B virus in cases of contamination with blood from people who have an acute or chronically persistent infection with this virus, and thus have high concentrations of infectious particles in the blood. Such accidents occur primarily in medical personnel by needlestick injury (10.1007/978-3-642-20718-1_19). In certain cases, the administration is performed in combination with an active vaccination (active–passive immunization). Specific immunoglobulin preparations are also administered when people have been bitten by animals that may be infected with the rabies virus (10.1007/978-3-642-20718-1_15). In the case of early application (together with an active vaccination), the antibodies can neutralize the virus, and impede its spread in the body. Since the time between contact with the virus and its spread in the organism is often very short, passive immunization is limited to a period shortly before or after exposure to the infective agent (usually within 4 days). Therefore, it is reserved for cases in which the contact with the potential pathogen is well documented and the type of infection is known, and when an appropriate immunoglobulin preparation is available. The protection afforded by antibody preparations lasts just a few weeks, as immunoglobulins are rapidly degraded in the organism. Therefore, postexposure administration of active vaccines is increasingly preferred, e.g. in the context of outbreak-control vaccination. In veterinary medicine, passive immunization is employed occasionally in young animals which were born in a flock with high infection pressure. This approach is applied, for example, in kennels when infections occur with canine parvovirus (10.1007/978-3-642-20718-1_20). However, its value is controversial, as the immunoglobulins administered hinder the more advantageous active immunization.