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Subunit

Rather than introducing an inactivated or attenuated micro-organism to an immune system (which would constitute a "whole-agent" vaccine), a subunit vaccine uses a fragment of it to create an immune response. One example is the subunit vaccine against hepatitis B, which is composed of only the surface proteins of the virus (previously extracted from the blood serum of chronically infected patients but now produced by recombination of the viral genes into yeast). Another example is edible algae vaccines, such as the virus-like particle (VLP) vaccine against human papillomavirus (HPV), which is composed of the viral major capsid protein. Another example is the hemagglutinin and neuraminidase subunits of the influenza virus. A subunit vaccine is being used for plague immunization.