A virus is a microorganism that functions and replicates only inside the living cells of other organisms known as host cells. It causes damage to the host cells and often kills the host cell in the process. Some common examples of human diseases caused by viruses are common cold, SARS, influenza, chickenpox, cold sores, rabies, Ebola virus disease, AIDS (HIV), avian influenza, etc. Vaccinations are the most effective method for preventing viral diseases as they provide immunity against infections. Another method of dealing with viruses is the use of antiviral drugs that selectively interfere with the replication of virus. There are multiple types of vaccines based on how they are prepared; and these include live-attenuated vaccines, inactivated vaccines, toxoid vaccines, mRNA vaccines, and viral vector vaccines. Due to large-scale vaccination drives, there has been a considerable decline in morbidity and mortality associated with viral infections such as polio, measles, mumps, and rubella. This book provides a comprehensive understanding of the role of vaccines in the treatment of viral infections. It will serve as a valuable source of reference to students, virologists, public health experts, and clinicians.