Socioeconomic and political
problems prevent many developing
nations from receiving vaccines
•
Inability to develop effective vaccines
for some pathogens
•
Vaccine-associated risks discourage
investment in developing new
vaccines
Vaccination Problems
•
3 general types of vaccines
–
Attenuated (live)
–
Killed (inactivated)
–
Toxoid
Vaccine Types
Also called modified live vaccines
•
Uses pathogens that are living but
have reduced virulence so they don’t
cause disease
•
Attenuation is the process of reducing
virulence
–
Viruses often attenuated by raising them in tissue
culture cells for which they aren’t adapted until
they lose the ability to produce disease
–
Bacteria can be made avirulent by culturing
under unusual conditions or through genetic
manipulation
Attenuated Vaccines
•
Can result in mild infections but no
disease
•
Contain replicating microbes that can
stimulate a strong immune response due
to the large number of antigen molecules
•
Viral vaccines trigger a cell-mediated
immune response dominated by T
H
1 and
cytotoxic T cells
•
Vaccinated individuals can infect those
around them, providing herd immunity
Attenuated Vaccines
•
Attenuated microbes may retain enough
virulence to cause disease, especially in
immunosuppressed individuals
•
Pregnant women should not receive live
vaccines due to the risk of the modified
pathogen crossing the placenta
•
Modified viruses may occasionally revert
to wild type or mutate to a virulent form
Problems with Attenuated
Vaccines
•
Can be either whole agent vaccines
produced with deactivated but whole
microbes, or subunit vaccines produced
with antigenic fragments of microbes
•
Both types are safer than live vaccines
since they cannot replicate or mutate to a
virulent form
•
When microbes are killed must not alter
the antigens responsible for stimulating
protective immunity
Inactivated Vaccines
Inactivated Vaccines (cont.)
•
Formaldehyde is commonly used to
inactivate microbes by cross-linking their
proteins and nucleic acids
•
Recognized as exogenous antigens and
stimulate a T
H
2 response that promotes
antibody-mediated immunity
•
Do not stimulate herd immunity
•
Whole agent vaccines may
stimulate a inflammatory response
due to nonantigenic portions of the
microbe
•
Antigenically weak since the
microbes don’t reproduce and don’t
provide many antigenic molecules
to stimulate the immune response
Problems with Inactivated
Vaccines
•
Administration in high or multiple
doses, or the incorporation of an
adjuvant, can make the vaccine more
effective
–
Adjuvants are substances that increase
the antigenicity of the vaccine
–
Adjuvants may also stimulate local
inflammation
–
High and multiple vaccine doses may
produce allergic reactions
Problems with Inactivated
Vaccines
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