There are two different types of flu vaccines, trivalent and quadrivalent.
Trivalent vaccines protect against 3 strains of the flu, A/H3N2, A/H1N1, and influenza B. Trivalent vaccines are available in:
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Traditional flu shots, approved for anyone 6 months and older
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Intradermal shots, which use a shorter needle, approved for anyone 18-64
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High dose shots approved for people over 65
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Cell based shots created using viruses grown in animal cells and approved for anyone over 18
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Recombinant shots created using DNA technology, approved for people 18-49 with severe egg allergies
Quadivalent vaccines protect against 4 strains of the flu, A/H3N2, A/H1N1, and 2 strains of influenza B. Quadrivalent vaccines are available in:
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Traditional flu shots, approved for anyone 6 months and older
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Nasal spray, approved for healthy people from 2-49, except
pregnant women
The flu vaccine will protect you for one flu season.
Detail :
http://www.flu.gov/prevention-vaccination/vaccination/
Thanks & Regards
Rajendra Tripathy.