Final answer:
A monovalent vaccine is a vaccine prepared from only one strain or species of microorganism. It provides immunity against a single pathogen and is particularly effective against diseases that do not mutate frequently, allowing the same vaccine formulation to be used over time.
Step-by-step explanation:
Definition of a Monovalent Vaccine
A monovalent vaccine is a type of vaccine that is prepared from only one strain or species of microorganism. In other words, it targets a single pathogen or a single strain of a pathogen. This is in contrast to polyvalent vaccines, which are designed to immunize against two or more strains or species of microorganisms. The key goal of a monovalent vaccine is to provide immunity against a specific pathogen, and they are especially useful when the pathogen doesn't mutate frequently, allowing the same vaccine to be used over a long period of time as seen with diseases like measles, mumps, and rubella, which have low mutation rates.
One common example of a pathogen that requires continuous vaccine redesign is influenza. Because of its high mutation rate, new influenza vaccines need to be developed frequently to keep up with the changing strains. On the other hand, measles, mumps, and rubella viruses mutate so infrequently that the same monovalent vaccines can provide long-term protection against these diseases.