Microorganisms and Disease
The influenza vaccine is administered each year because

the vaccine is sufficiently toxic to make it necessary to administer only a small amount at any one time
mutations in the viral hemagglutinin may allow the virus to evade the immune response elicited by previous vaccines
it is a polysaccharide vaccine that does not confer long-term protection
None of these

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Microorganisms and Disease
Prontosil is

an effective antibacterial when used in in-vitro cultures
an effective antibacterial when used in animals
an effective antibacterial both in animals as well as in in-vitro cultures
not used as an antibacterial agent

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