Final answer:
Attenuated viruses induce long-term immunity because they multiply slowly in the host, allowing the immune system to develop a comprehensive response without causing severe symptoms, thus mimicking a natural infection and providing effective immunization.
Step-by-step explanation:
Attenuated viruses often induce long-term immunity because they multiply slowly in the recipient and stimulate the immune system in a manner that mimics the wild-type strain. Live attenuated vaccines are created by weakening the disease-causing virus in the laboratory, so when introduced to the host, these viruses can still cause infection but do not grow very well. This allows the host’s immune system to develop an appropriate response over time, which can prevent major disease and lead to long-lasting immunity.
Moreover, the slow replication afaids in the maturation of a comprehensive immune response, involving both cellular and humoral immunity, and the development of memory cells. As a result, the host gains the ability to respond quickly to future exposures to the pathogen. However, there is a low but serious risk that these viruses might undergo back mutations to the disease-causing form.
In summary, because these attenuated viruses replicate at a pace that is slow enough for the immune response to develop without causing severe symptoms, they provide an effective vaccine strategy for long-term protection against various diseases.