Introduction Infectious diseases are diseases which are clinically proved to be caused by pathogenic microbial organisms ,such has viruses , bacteria, multicultural parasites, protozoa, fungi and deviant proteins well-known as prions. These pathogenic microbial organisms are capable of causing disease in both plants animals. Infectious diseases are sometimes referred to as contagious diseases or communicable diseases. Ways in which infectious diseases are transmitted Transmission of infectious diseases may arise through different mechanisms depending on the type of diseases, for instance, infectious Respiratory diseases are usually transmitted through contact with infected droplets by coughing, kissing, singing, sneezing and talking. Gastrointestinal infectious diseases are frequently transmitted through ingestion of infected water and food with infectious pathogenic microbes. Infectious Sexually transmitted illnesses are usually transmitted through unprotect sex with infected person with infectious disease. Furthermore these diseases are easily transmitted through contact with infected objects such as towels and coins. In addition infectious pathogenic microbes may also penetrate through the skin surfaces. Finally infectious diseases can be transmitted through biological or mechanical vectors such have mosquitoes and butterflies respectfully (Weber, 2004). Importance of vaccines and immunization in prevention of infectious diseases Vaccination and immunization have been used globally in preventing, eradicating and controlling infectious diseases ,for instance the world health organization have eradicated successfully small pox disease, in the world today through immunizations programmer and campaigns. Vaccination and immunization help in preventing the occurrence of a disease and if they do, disease burden is reduced, and death is avoided. Vaccines work in such way that, when a person is immunized against a particular disease, the person reacts to the foreign antigens by producing antibodies which fight against the foreign antigens, in addition memory cells are created which assist the immunity system to fight against the new infection attacks of a that particular disease, these memories normally last for many years or even for a life time (Slenczka, 1999). Importance of emerging and re-emerging diseases Emerging and re-emerging infections are diseases of public health importance and their infection s occurrence rates in humans’ beings is increasing every year and even intimidates to rise in the near future. Examples of these diseases are bird flue, dengue fever, rabies, malaria, Ebola and many other diseases of infectious origin. Many aspects, or a group of factors, contribute to the emergency and re-emergency of these infectious diseases for instance societal factors, availability and accessibility of health care, human behavior, food production and environmental and climatically changes. New infectious illness may materialize from genetic modification in existing pathogenic organisms; well known infectious diseases may be extended to new populations and geographic regions and; and due changes in climatically conditions increasing the variability of humans to infectious diseases, unknown infectious disease may emerge