210: Chapter 17

What was the impact of vaccines by the late 1900s?

• Greatly reduced cases of many infectious diseases

• Improved global public health

What disease has been successfully eradicated through vaccination?

Smallpox

What diseases are targeted for potential worldwide eradication?

• Polio

• Measles

• Mumps

• Rubella

What is a modern advancement in immunization beyond infectious diseases?

Vaccines are now available against some types of cancer

What is active artificially acquired immunization?

• Immunity gained through vaccines

• Antigens are introduced in a controlled way

• Body produces its own antibodies and memory cells

How are pathogens used in vaccines modified?

• Altered or inactivated

• Made less likely to cause disease

• Still trigger an immune response

How is vaccine effectiveness measured?

By measuring antibody titer in blood

• Titer = concentration of IgG and IgM antibodies

5 Types of vaccines

• Attenuated (Modified Live) Vaccines

• Inactivated (Killed) Vaccines

• Toxoid Vaccines

• Combination Vaccines of 2+ vaccines

• Vaccines Using Recombinant Gene Technology

What are some risks of vaccines?

• Mild side effects (fever, soreness, fatigue)

• Temporary immune reactions (inflammation, swelling)

• Rare allergic reactions

• Very rare serious adverse effects

• Some vaccines may not produce strong immunity in all individuals

What are the benefits of vaccination/immunization?

• Prevents infectious diseases

• Reduces severity of illness if infection occurs

• Creates immune memory for long-term protection

• Protects vulnerable populations (herd immunity)

• Has led to eradication or reduction of diseases (e.g., smallpox)

• Helps prevent spread of outbreaks in communities

Why is vaccination considered important for public health?

• Reduces transmission of infectious diseases

• Lowers overall disease rates in populations

• Protects people who cannot be vaccinated

What are attenuated (modified live) vaccines?

• Contain live pathogens with reduced virulence

• Can still replicate

• Causes a mild infection that triggers immunity

(Active virus stimulates strong immune response, causes mild infection)

Why do attenuated vaccines produce a strong immune response?

• Live organisms stimulate the immune system strongly

• Activate both antibody and cell-mediated immunity

What are the pros of attenuated vaccines?

• Very effective immune response

• Long-lasting immunity

• Stimulate both humoral and cell-mediated immunity

• Can spread to others and provide indirect “contact immunity”

What is contact immunity in attenuated vaccines?

• Vaccinated person may shed weakened virus

• Can expose others and indirectly stimulate immunity

What are the risks of attenuated vaccines?

• May cause disease in immunocompromised individuals (modified microbes may retain enough residual virulence)

• Not safe for pregnant women

• Rare chance of reverting to virulent (wild-type) form

How are attenuated (live) vaccines made?

• A whole live pathogen is grown in culture (LOTS of complex antigens)

• Then repeatedly sub-cultured for many generations

What happens to a pathogen during vaccine attenuation?

• It adapts to a “hospitable” lab environment

• Virulence genes mutate or lose function over time

• Becomes less able to cause disease

Why does sub-culturing weaken a pathogen?

• Natural selection favors survival in lab conditions

• Virulence is not needed in culture

• Mutations reduce disease-causing ability

What type of immune stimulus do attenuated vaccines provide?

• Whole “live” pathogen with many complex antigens

• Strong immune system activation

What is an example of an attenuated (live) vaccine combination?

MMR vaccine

• Protects against measles, mumps, and rubella

What is another example of an attenuated vaccine?

Chickenpox (Varicella-Zoster virus) vaccine

What are inactivated (killed) vaccines?

• Pathogens are killed and cannot replicate

• Cannot mutate, revert, or cause infection

• Still contain antigens to stimulate immunity

What are the two types of inactivated vaccines?

Whole-agent vaccines

Subunit vaccines

Whole agent vaccines

Deactivated but whole microbes

• Entire microbe is killed

• Still contains full set of antigens

• Cannot cause disease

Subunit vaccines

Antigenic fragments of microbes

• Contains only parts of the microbe

• Uses antigenic fragments

• More targeted immune response

What are the advantages of inactivated vaccines?

• Safe (cannot replicate or revert)

• Stimulate antibody (humoral) immune response

• Good for immunocompromised individuals

What are the disadvantages of inactivated vaccines?

• Weaker immune response than live vaccines (microbes do not replicate and provide many antigenic molecules)

• Often require booster doses or high doses

• No contact immunity stimulated

• Nonantigenic portions occasionally stimulate painful inflammatory

  response

Why do inactivated vaccines often need adjuvants?

• They increase antigen effectiveness

• Help strengthen immune response

What is a key limitation of inactivated vaccines regarding immunity spread?

• No contact immunity

• Cannot replicate in the body

What side effect can sometimes occur with inactivated vaccines?

• Local inflammatory reactions

• Sometimes due to non-antigenic components

Why don’t inactivated (killed) vaccines strongly stimulate the cell-mediated immune response?

• Cell-mediated immunity (T cells) is best activated by live, intracellular infection

• Inactivated vaccines do not replicate inside host cells

• Therefore, antigens are mainly presented as exogenous antigens (MHC II pathway)

• This mainly activates B cells and antibody production, not strong TC cell responses

• Weak intracellular “danger signals” → weak T cell activation

What are toxoid vaccines?

• Chemically or thermally inactivated toxins

• Used to stimulate active immunity

• Teach the immune system to recognize toxins

What type of immunity do toxoid vaccines stimulate?

• Antibody-mediated (humoral) immunity

• Strong B cell/antibody response

What are the advantages of toxoid vaccines?

• Stimulate antibody production

• Provide protection against toxin-producing bacteria

What are the disadvantages of toxoid vaccines?

• Require multiple doses in childhood

• Need boosters about every 10 years

• Contain few epitopes → weaker stimulation

Why don’t toxoid vaccines strongly stimulate cell-mediated immunity?

• They are inactivated toxins, not living pathogens

• Do not trigger strong intracellular infection signals

• Mainly activate B cells, not T cells

Give an example of a toxoid vaccine.

Tetanus vaccine

What kind of memory cells are produced after toxoid vaccination?

• Mainly memory B cells

• Because toxoid vaccines stimulate antibody (humoral) immunity

• Little to no strong memory T cell (cell-mediated) response

• Overall memory is focused on antibody production against the toxin

What are recombinant DNA vaccine techniques?

• Use genetic engineering to modify pathogens or their genes

• Can remove virulence genes or produce specific antigens

How are virulence genes used in recombinant vaccine development?

• Virulence genes are selectively deleted

• Pathogen becomes safe but still antigenic

How do recombinant techniques improve vaccine production?

• Produce large amounts of very pure antigens

• Allow precise targeting of immune response

• Reduce risk of infection

What are live recombinant vaccines?

• Live organisms genetically modified to express antigens

• Stimulate strong immune responses

What are DNA vaccines?

• Use genetic material (DNA) encoding antigens

• Host cells produce the antigen internally

• Triggers immune response without whole pathogen

Why are recombinant vaccines considered advanced?

• Highly specific antigen targeting

• Safe (no full virulent pathogen needed)

• Can be mass-produced efficiently

How does an mRNA vaccine enter the body?

• Delivered in a lipid RNA nanoparticle via syringe

• Enters human cells after injection

What happens when the mRNA vaccine enters a cell?

• Lipid capsule fuses with the cell membrane

• Releases mRNA (genetic instructions) into the cytoplasm

What does the cell do with the mRNA from a vaccine?

• Ribosomes read the mRNA instructions

• Cell produces the target (viral) protein

What happens to the mRNA after it is used?

• mRNA is broken down by the cell

• It does not stay in the body long-term

How does the immune system respond to an mRNA vaccine?

• Cell displays the target protein on its surface

• Immune system recognizes it as foreign

• Triggers antibody and T cell response

What immune outcome does an mRNA vaccine produce?

• Formation of memory B and T cells (plus active and plasma cells)

• Faster response upon future infection

Why are mRNA vaccines considered safe?

• Do not contain live virus

• Do not alter DNA

• mRNA is quickly degraded after protein production

What are combination vaccines?

• Vaccines that contain two or more vaccines in one injection

• Protect against multiple diseases at the same time

Why are combination vaccines used?

• Reduce number of injections needed

• Improve vaccination compliance

• Provide protection against multiple pathogens efficiently

What is a benefit of combination vaccines on the immune system?

• Stimulate immune responses to multiple antigens at once

• Still produce memory cells for each component vaccine

What is a potential advantage of combination vaccines for patients?

• Fewer shots and clinic visits

• Less discomfort and better schedule adherence

What is a disadvantage of combination vaccines (2+ vaccines in one shot)?

• More complex immune exposure at once may slightly increase side effects

• Harder to determine which component caused a reaction if side effects occur

• Some antigen combinations may reduce individual immune response strength

• Can be more difficult to develop and standardize compared to single vaccines

What is immunization?

• Process that protects individuals from infectious disease

• Helps slow the spread of contagious diseases in populations

How does immunization affect disease spread?

• Reduces number of susceptible individuals

• Slows or stops transmission of pathogens in a community

What is herd immunity?

• Protection of a population when most people are immune

• Makes it difficult for a pathogen to spread

At what level of immunity does herd immunity typically occur?

Usually when ~75% or more of the population is immune

Why does herd immunity protect unvaccinated individuals?

• Pathogen cannot easily spread between people

• Breaks chains of transmission

What are common minor risks of vaccines?

• Pain at injection site

• Mild malaise (feeling unwell)

• Fever

What are rare but serious risks of vaccines?

• Anaphylactic shock (severe allergic reaction)

• Very rare residual virulence in attenuated vaccines

What vaccine-related claims are NOT supported by research?

Vaccines do NOT cause autism, diabetes, or asthma

How have vaccines changed in safety over time?

• Modern vaccines are significantly safer than older versions

• Improved purification and technology reduce risks

What is a limitation of passive immunotherapy?

• Can cause serum sickness (allergic reaction)

• Temporary protection only (antibodies degrade)

• No immune immune memory B cells are formed

Why doesn’t passive immunotherapy provide long-term immunity?

• Patient does not produce their own antibodies

• No activation of memory immune cells