Limitations of Vaccines
Vaccines bolster the body's immune system to better attack viruses in the "complete particle" stage, outside of the organism's cells. They traditionally consist of an attenuated (weakened or killed) version of the virus. These vaccines can, in rare cases, harm the host by inadvertently infecting the host with a full-blown viral occupancy. Recently "subunit" vaccines have been devised that consist strictly of protein targets from the pathogen. They stimulate the immune system without doing serious harm to the host. In either case, when the real pathogen attacks the subject, the immune system responds to it quickly and blocks it.
Vaccines are very effective on stable viruses, but are of limited use in treating a patient who has already been infected. They are also difficult to successfully deploy against rapidly mutating viruses, such as influenza (the vaccine for which is updated every year) and HIV. Antiviral drugs are particularly useful in these cases.
Read more about this topic: Antiviral Drug
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