The Immune System and Disease Prevention
3. Vaccination
Learning outcomes
- I can explain how vaccines work.
- I can describe the immune response triggered by vaccination.
- I can distinguish between vaccination and treatment.
- I can explain the concept of herd immunity.
- I can evaluate the role of vaccines in public health.
What Is Vaccination?
Vaccination is a method of preparing the immune system to recognize and respond to a particular pathogen.
A vaccine exposes the immune system to:
an antigen, or instructions that allow the body to produce an antigen.
This stimulates an immune response without requiring the person to experience the full disease that the vaccine is designed to prevent.
The immune system can then develop:
immunological memory.
If the real pathogen is encountered later, the immune system can respond more rapidly and effectively.
What Is a Vaccine?
A vaccine is a biological preparation designed to stimulate protective immunity against a particular infectious disease.
Different vaccines use different approaches.
They may contain:
- weakened pathogens
- inactivated pathogens
- parts of pathogens
- purified antigens
- harmless vectors carrying genetic instructions
- genetic instructions such as mRNA
Although the methods differ, the basic goal is the same:
teach the adaptive immune system to recognize a particular antigen.
Vaccines and Antigens
An antigen is a molecular structure that can be recognized by the adaptive immune system.
Pathogens contain many different antigens.
A vaccine introduces selected antigens, or information for producing them, so that the immune system can learn to recognize:
the target pathogen.
This occurs before the person encounters the actual disease.
The Immune Response to Vaccination
A simplified vaccine response can be represented as:
vaccination → antigen detected → lymphocytes activated → clonal expansion → antibodies and immune cells produced → memory cells remain
This is an example of:
adaptive immunity.
Step 1: Vaccination
The vaccine introduces an antigen, or instructions for producing an antigen, into the body.
The immune system recognizes this antigen as:
foreign.
Innate immune responses also help alert and activate the adaptive immune system.
Step 2: Antigen Presentation
Specialized immune cells can take up vaccine material and display antigen fragments.
This process is called:
antigen presentation.
Antigen-presenting cells include:
- dendritic cells
- macrophages
- B cells
Antigen presentation helps activate specific:
T lymphocytes.
Step 3: Lymphocyte Activation
The body contains many different B and T lymphocytes.
Only certain lymphocytes have receptors capable of recognizing a particular:
antigen.
When the correct cells encounter their matching antigen and receive the appropriate signals, they become:
activated.
Step 4: Clonal Expansion
Activated lymphocytes begin to divide.
This produces many cells capable of responding to the same antigen.
This process is called:
clonal expansion.
A small number of matching immune cells can therefore become:
a much larger population.
Step 5: Antibody Production
Activated B cells can develop into:
plasma cells.
Plasma cells produce:
antibodies.
Antibodies bind specifically to their matching antigens.
Depending on the pathogen, antibodies can:
- block infection of cells
- neutralize toxins
- mark pathogens for destruction
- help other immune mechanisms remove pathogens
Step 6: T-Cell Responses
Vaccination can also stimulate:
T lymphocytes.
Helper T cells help coordinate immune responses.
Some vaccines can also produce strong cytotoxic T-cell responses.
Cytotoxic T cells can recognize and destroy certain:
infected cells.
Therefore, protection does not depend only on antibodies.
Step 7: Memory Cells
After the initial immune response decreases, some B and T cells remain as:
memory cells.
These cells are extremely important.
They allow the immune system to remember the antigen for:
future encounters.
The Secondary Immune Response
Suppose the vaccinated person later encounters the actual pathogen.
Memory cells recognize the familiar:
antigen.
They can respond much more rapidly than during the original vaccine response.
The sequence becomes:
pathogen enters → antigen recognized → memory cells activate → rapid clonal expansion → strong immune response
The pathogen may be controlled before it causes serious disease.
Primary and Secondary Responses
First exposure
The immune system encounters an antigen for the first time.
The response takes time to develop.
This is the:
primary immune response.
Later exposure
Memory cells already exist.
The response is generally:
faster and stronger.
This is the:
secondary immune response.
Vaccination aims to create immune memory before exposure to the dangerous pathogen.
Vaccination Produces Active Immunity
Vaccination normally produces:
artificial active immunity.
It is:
artificial
because exposure occurs through vaccination.
It is:
active
because the person's own immune system responds and produces immune memory.
Different Types of Vaccines
Scientists have developed several vaccine technologies.
Important types include:
- live attenuated vaccines
- inactivated vaccines
- subunit vaccines
- toxoid vaccines
- viral vector vaccines
- mRNA vaccines
Each uses a different method to expose the immune system to appropriate:
antigens.
Live Attenuated Vaccines
A live attenuated vaccine contains a weakened form of a pathogen.
The pathogen has been altered so that it does not normally cause the disease it ordinarily would in people for whom the vaccine is appropriate.
Examples include vaccines against:
- measles
- mumps
- rubella
- chickenpox
Because the weakened pathogen can resemble natural infection closely, these vaccines can produce strong immune responses.
Inactivated Vaccines
An inactivated vaccine contains a pathogen that has been killed or otherwise made unable to reproduce.
The immune system can still recognize its:
antigens.
Examples include some vaccines against:
- polio
- hepatitis A
- influenza
Because the pathogen cannot reproduce, it cannot cause infection in the same way as the live pathogen.
Subunit Vaccines
A subunit vaccine contains selected components of a pathogen rather than the entire organism.
These components may include:
proteins or other antigens.
The immune system learns to recognize these specific structures.
An example is the:
hepatitis B vaccine.
Toxoid Vaccines
Some bacterial diseases are caused largely by:
toxins.
A toxoid vaccine contains an inactivated form of a toxin.
The immune system produces antibodies capable of recognizing the toxin.
Examples include vaccines against:
- tetanus
- diphtheria
The immune system is therefore prepared to neutralize the toxin if exposure occurs later.
Viral Vector Vaccines
A viral vector vaccine uses a modified virus to deliver genetic instructions for an antigen.
The vector enters some cells and provides instructions for producing the antigen.
The immune system then responds to:
that antigen.
The vector is designed so that it does not cause the disease being vaccinated against.
mRNA Vaccines
An mRNA vaccine contains messenger RNA carrying instructions for producing a particular antigen.
Cells temporarily use these instructions to make the antigen.
The immune system recognizes the antigen and develops:
adaptive immunity.
The mRNA is subsequently broken down by normal cellular processes.
Booster Vaccinations
Immune protection can decrease over time for some diseases.
A:
booster
is an additional vaccine dose given after the original vaccination series.
The booster exposes the immune system to the antigen again.
Memory cells respond, strengthening or refreshing the:
immune response.
Why Are Boosters Needed for Some Vaccines?
Several factors can influence how long vaccine protection lasts:
- type of vaccine
- characteristics of the pathogen
- changes in the pathogen
- age
- immune system differences
- time since vaccination
Some vaccines provide long-lasting protection after relatively few doses.
Others require periodic:
boosters.
Vaccination vs Treatment
Vaccination and treatment are not the same thing.
Vaccination
Usually occurs:
before disease develops.
Purpose:
prepare the immune system
Main goal:
prevention or reduction of disease
Treatment
Occurs when disease or infection is already present.
Purpose:
manage, control, or eliminate the disease
Examples include:
- antibiotics for susceptible bacterial infections
- antiviral medicines for some viral infections
- antifungal medicines
- supportive medical care
Prevention vs Cure
A vaccine generally does not work by:
curing an existing infection.
Instead, vaccination prepares the immune system for possible future exposure.
Therefore:
vaccination = prevention
while:
treatment = response to an existing medical problem
There are some specialized therapeutic vaccines, but routine infectious-disease vaccines are primarily preventive.
Why Vaccinate Before Exposure?
Adaptive immunity takes time to develop during the first encounter with an antigen.
If immune memory already exists when the pathogen arrives:
the response can begin much faster.
This gives the immune system an important advantage.
Vaccination and Disease Severity
Vaccines do not always prevent every:
infection.
Depending on the disease and vaccine, vaccination may reduce the probability of:
- infection
- symptoms
- severe illness
- hospitalization
- complications
- death
Therefore, vaccine effectiveness must be considered in relation to the particular:
outcome being measured.
What Is Herd Immunity?
Vaccination can protect individuals.
It can also sometimes provide protection at the:
population level.
When enough people in a population are immune to an infectious disease, transmission becomes more difficult.
This population effect is commonly called:
herd immunity or community immunity.
How Herd Immunity Works
Imagine a contagious pathogen enters a population.
If almost everyone is susceptible:
infected → susceptible → susceptible → susceptible
The pathogen has many opportunities to spread.
If many people are immune:
infected → immune barrier → transmission chain interrupted
The pathogen has fewer opportunities to reach susceptible people.
Breaking Chains of Transmission
Community immunity works because infectious disease often spreads through:
chains of transmission.
If immunity prevents enough links in those chains, sustained transmission becomes more difficult.
Therefore:
more immunity → fewer successful transmissions → fewer opportunities for large outbreaks
The exact relationship depends on the pathogen and how well immunity prevents infection or transmission.
Herd Immunity Does Not Mean Everyone Is Immune
Even when community immunity is strong, some people may remain:
susceptible.
These may include:
- people who cannot receive a particular vaccine
- people whose immune systems respond poorly to vaccination
- some infants who are too young for certain vaccines
- people whose immunity has decreased
Reduced transmission can indirectly help protect these individuals.
Herd Immunity Threshold
The proportion of people who need immunity to strongly reduce sustained transmission is sometimes called the:
herd immunity threshold.
This threshold is not the same for every disease.
It depends on factors including:
- how easily the pathogen spreads
- how effectively immunity prevents transmission
- contact patterns
- distribution of immunity through the population
Highly contagious diseases generally require a:
higher level of population immunity.
Measles and Community Immunity
Measles is extremely contagious.
If vaccination coverage falls and susceptible people accumulate, outbreaks can occur.
This is why maintaining high vaccination coverage is especially important for diseases such as:
measles.
Herd Immunity and Different Vaccines
Not every vaccine produces the same population effect.
A vaccine that strongly prevents infection and transmission can contribute substantially to:
community immunity.
A vaccine that mainly reduces severe disease but has less effect on infection may provide excellent individual protection while having a smaller effect on:
transmission.
Therefore, herd immunity depends on the characteristics of both the vaccine and the pathogen.
Vaccines and Public Health
Public health focuses on protecting and improving the health of populations.
Vaccination is one of several tools used to prevent infectious disease.
Vaccination programs can:
- reduce disease incidence
- reduce severe illness
- prevent complications
- reduce deaths
- reduce outbreaks
- protect vulnerable people
- reduce pressure on healthcare systems
- contribute to disease elimination or eradication
Smallpox
One of the most important examples of vaccination in public health is:
smallpox.
Smallpox was a severe infectious disease caused by variola virus.
A coordinated global vaccination program eventually eliminated transmission.
In 1980, the World Health Organization declared:
smallpox eradicated.
Eradication
Eradication means reducing the worldwide incidence of an infectious disease to:
zero,
with no continuing natural transmission.
Eradication is extremely difficult.
Smallpox remains the major example of a human infectious disease eradicated globally through coordinated public-health action, with vaccination playing a central role.
Elimination
Elimination is different from eradication.
Elimination usually refers to reducing transmission of a disease to zero, or to a defined very low target, within a particular:
geographic area.
A disease eliminated from one country may still exist elsewhere and can potentially be:
reintroduced.
Polio Vaccination
Vaccination has dramatically reduced:
poliomyelitis, or polio.
Polio once caused large outbreaks and paralysis in many countries.
Global vaccination programs have eliminated wild poliovirus from most of the world, although eradication efforts continue.
This demonstrates both the power and the difficulty of international vaccination programs.
Vaccination and Measles
Measles vaccination has greatly reduced disease where high coverage is maintained.
However, measles can return when:
susceptible populations accumulate.
This illustrates an important principle:
successful vaccination programs must often be maintained even after a disease becomes uncommon.
Why Vaccination Programs Can Become Victims of Their Own Success
When vaccination greatly reduces a disease, people may stop seeing its effects.
The disease can begin to seem:
unimportant.
If vaccination coverage then falls, susceptible individuals accumulate.
The disease may return.
Therefore, low disease prevalence can actually be evidence that prevention programs are:
working.
Evaluating Vaccine Benefits
When evaluating a vaccine, scientists consider evidence about:
- effectiveness
- safety
- duration of protection
- reduction in severe disease
- effect on transmission
- disease burden
- population characteristics
A scientific evaluation should compare:
benefits and risks using evidence.
Vaccine Safety
Vaccines are tested before widespread use and continue to be monitored afterward.
Scientists examine:
- common side effects
- rare adverse events
- effectiveness
- safety in different populations
No medical intervention is completely:
risk-free.
The important scientific question is how the risks associated with vaccination compare with the risks of the disease and the expected benefits of vaccination.
Common Vaccine Reactions
Vaccination activates the immune system.
This can sometimes produce temporary effects such as:
- soreness at the injection site
- tiredness
- headache
- mild fever
- muscle aches
These symptoms often reflect:
immune activation.
They are not necessarily signs that the vaccine has caused the disease.
Rare Adverse Events
Some vaccines can have rare serious adverse effects.
This is why vaccine safety is monitored even after a vaccine has been:
approved and introduced.
Large vaccination programs can detect extremely rare events that might not appear during smaller clinical trials.
Vaccine Effectiveness
Vaccine effectiveness describes how well a vaccine performs under real-world conditions.
Effectiveness may be measured against different outcomes.
For example:
effectiveness against infection
is not necessarily the same as:
effectiveness against severe disease.
When interpreting vaccine data, it is important to ask:
Effective against what outcome?
No Vaccine Is Necessarily 100% Effective
A vaccinated person may sometimes still become infected.
This does not automatically mean that the vaccine:
failed completely.
The vaccine may still reduce:
- disease severity
- complications
- hospitalization
- transmission
- duration of illness
Protection exists on a spectrum rather than always being simply:
protected or unprotected.
Why Vaccination Programs Require Monitoring
Pathogens and populations can change.
Public-health authorities therefore monitor:
- disease cases
- vaccination coverage
- vaccine effectiveness
- adverse events
- pathogen variants
- population immunity
Recommendations may change when new evidence becomes available.
This is an example of science responding to:
new data.
Vaccine Development
Developing a vaccine involves several stages.
A simplified process is:
identify pathogen and antigens
↓
design vaccine candidate
↓
laboratory and preclinical studies
↓
clinical trials
↓
regulatory evaluation
↓
manufacturing and distribution
↓
continued safety and effectiveness monitoring
Clinical Trials
Vaccines are tested in clinical trials.
Different phases investigate questions such as:
- Is the vaccine acceptably safe?
- What dose should be used?
- Does it produce an immune response?
- Does it reduce the targeted disease outcome?
- What side effects occur?
Larger trials provide more information about:
effectiveness and safety.
Continued Monitoring
Monitoring does not stop when a vaccine is introduced.
Health systems continue collecting information from:
large populations.
This helps scientists identify:
- rare adverse events
- changing effectiveness
- duration of protection
- effects in different groups
Public-health decisions can then be updated using new evidence.
Challenges for Vaccination Programs
Vaccination programs can face challenges including:
- vaccine availability
- cost
- transportation
- refrigeration
- access to healthcare
- conflict and displacement
- misinformation
- vaccine hesitancy
- changing pathogens
- unequal global distribution
A vaccine can only protect populations if it can actually reach the people who:
need it.
The Cold Chain
Some vaccines must be stored within particular temperature ranges.
The system used to keep vaccines at appropriate temperatures during:
storage and transportation
is called the:
cold chain.
Maintaining the cold chain can be difficult in remote areas or places with unreliable infrastructure.
Vaccine Hesitancy
Vaccine hesitancy refers to delay in acceptance or refusal of vaccination despite the availability of vaccination services.
The reasons can be complex and may include:
- concerns about safety
- misinformation
- mistrust
- cultural factors
- previous experiences
- access difficulties
Clear communication and trustworthy evidence are important in addressing these concerns.
Vaccination and Antibiotics
Vaccines and antibiotics have completely different purposes.
Vaccine
Used primarily to:
prevent particular infectious diseases
Works by:
stimulating immune memory
Antibiotic
Used to:
treat susceptible bacterial infections
Works by:
killing bacteria or preventing their growth
Antibiotics do not replace vaccination.
Vaccines do not act like antibiotics.
Vaccination and Antiviral Drugs
An antiviral drug generally acts against a virus during or around an:
infection.
A vaccine primarily prepares the immune system:
before future exposure.
Therefore:
antiviral = treatment or prevention through a drug acting on viral processes
vaccine = immune preparation
Worked Example 1
A vaccine introduces an antigen.
What happens next?
Specific lymphocytes recognize the antigen and become:
activated.
They undergo clonal expansion and produce effector and memory cells.
Worked Example 2
A B cell is activated after vaccination.
What can it become?
It may differentiate into a:
plasma cell
that produces antibodies or into a:
memory B cell.
Worked Example 3
A vaccinated person encounters the pathogen several years later.
Their immune system responds rapidly.
Why?
They already possess:
memory cells
capable of recognizing the pathogen's antigen.
Worked Example 4
A person receives antibiotics after developing a bacterial infection.
Is this vaccination?
No.
The antibiotics are being used as:
treatment.
Vaccination primarily prepares immunity before disease occurs.
Worked Example 5
Most members of a population are immune to a particular infectious disease.
An infected person enters the population, but transmission chains repeatedly encounter immune individuals.
What population effect is being demonstrated?
Herd immunity, or community immunity.
Worked Example 6
A vaccine prevents severe disease very effectively but only partially prevents infection.
Can vaccinated people still become infected?
Yes.
Protection against infection and protection against severe disease are different:
outcomes.
Worked Example 7
Vaccination coverage falls substantially for a highly contagious disease.
What may happen?
The number of susceptible people may:
increase.
This can make sustained transmission and outbreaks more likely if the pathogen is introduced.
Worked Example 8
A vaccine causes temporary arm soreness and a mild fever.
Does this automatically mean the vaccine caused the infectious disease?
No.
Temporary symptoms may result from:
immune activation.
Evaluating Vaccination in Public Health
A complete evaluation should consider both individual and population effects.
Individual level
Vaccination may:
- reduce risk of disease
- reduce severe illness
- reduce complications
- create immune memory
Population level
Vaccination programs may:
- reduce transmission for diseases where vaccines limit infection or infectiousness
- reduce outbreaks
- indirectly protect vulnerable people
- reduce healthcare burden
- contribute to elimination or eradication
Challenges
Programs must also consider:
- safety
- access
- cost
- logistics
- public trust
- vaccine effectiveness
- pathogen evolution
Therefore, vaccination is both an:
immunological tool
and a:
public-health strategy.
Common Mistake: Vaccines Kill Pathogens Directly
Vaccines generally do not directly attack pathogens.
Instead, they:
prepare the immune system.
Antibodies, immune cells, and other defenses respond when the pathogen is encountered.
Common Mistake: Vaccination and Treatment Are the Same
Vaccination is primarily:
preventive.
Treatment is used to manage an infection or disease that already exists.
Common Mistake: Vaccines Always Prevent Infection Completely
Different vaccines provide different forms and levels of protection.
Some strongly prevent infection.
Others may be particularly effective at preventing:
severe disease.
Common Mistake: Herd Immunity Means Everyone Is Vaccinated
Community immunity depends on the amount and distribution of:
effective immunity.
Not every person must necessarily be immune for transmission to decrease.
However, the required level varies considerably among diseases.
Common Mistake: Herd Immunity Protects an Individual Completely
Community immunity:
reduces opportunities for transmission.
It does not guarantee that a susceptible individual cannot become infected.
Common Mistake: Vaccines Weaken the Immune System
Vaccination stimulates the adaptive immune system to:
develop a specific response and memory.
The purpose is to prepare immune defenses for later exposure.
Common Mistake: A Disease Becoming Rare Means Vaccination Is No Longer Needed
If a pathogen is still circulating somewhere, falling vaccination coverage can allow:
susceptible populations to accumulate.
The disease may then return.
Check Your Understanding
1. Define vaccination.
2. What is a vaccine?
3. What is an antigen?
4. Why are antigens important in vaccination?
5. Describe the immune response that occurs after vaccination.
6. What is antigen presentation?
7. What happens when a matching lymphocyte recognizes a vaccine antigen?
8. What is clonal expansion?
9. What is the role of plasma cells?
10. What is an antibody?
11. How can antibodies protect against infection?
12. What role can T cells play after vaccination?
13. What are memory cells?
14. Why are memory cells important?
15. Compare the primary and secondary immune responses.
16. Why is the immune response usually faster after later exposure?
17. What type of immunity is normally produced by vaccination?
18. What is a live attenuated vaccine?
19. What is an inactivated vaccine?
20. What is a subunit vaccine?
21. What is a toxoid vaccine?
22. Explain how an mRNA vaccine works.
23. What is a booster vaccination?
24. Why are boosters required for some vaccines?
25. Explain the difference between vaccination and treatment.
26. Why is vaccination normally given before disease develops?
27. Define herd immunity.
28. Explain how community immunity can interrupt chains of transmission.
29. How can community immunity help protect susceptible people?
30. Why is there no single herd immunity threshold for every disease?
31. Why do highly contagious diseases generally require high levels of population immunity?
32. Explain why a vaccine does not necessarily need to prevent every infection to provide important protection.
33. What is vaccine effectiveness?
34. Why must we specify the outcome when discussing vaccine effectiveness?
35. Give three benefits of vaccination programs to public health.
36. How did vaccination contribute to smallpox eradication?
37. Why can diseases return when vaccination coverage falls?
38. Why is continued vaccine safety monitoring important?
39. Give three challenges involved in running vaccination programs.
40. Explain how vaccination can protect an individual while also contributing to protection at the population level.
Key Terms
- Vaccination: Administration of a vaccine to stimulate protective immunity.
- Vaccine: Biological preparation designed to stimulate immunity against a disease.
- Antigen: Molecular structure recognized by the adaptive immune system.
- Antibody: Specific antigen-binding protein produced by plasma cells.
- B lymphocyte: Immune cell involved in antibody-mediated adaptive immunity.
- T lymphocyte: Immune cell involved in coordinating responses or attacking infected cells.
- Plasma cell: Activated B-cell descendant that produces antibodies.
- Memory cell: Long-lived immune cell that enables a rapid response during later exposure.
- Clonal expansion: Multiplication of activated antigen-specific lymphocytes.
- Primary immune response: Adaptive response following first exposure to an antigen.
- Secondary immune response: Faster response following later exposure to the same antigen.
- Active immunity: Immunity generated by a person's own immune response.
- Artificial active immunity: Active immunity produced through vaccination.
- Booster: Additional vaccine dose used to strengthen or restore immunity.
- Live attenuated vaccine: Vaccine containing a weakened form of a pathogen.
- Inactivated vaccine: Vaccine containing a pathogen that cannot reproduce.
- Subunit vaccine: Vaccine containing selected components of a pathogen.
- Toxoid vaccine: Vaccine containing an inactivated bacterial toxin.
- Viral vector vaccine: Vaccine using a modified virus to deliver genetic instructions for an antigen.
- mRNA vaccine: Vaccine containing messenger RNA instructions for producing an antigen.
- Herd immunity: Population-level reduction in transmission when enough people have effective immunity.
- Vaccine effectiveness: Measurement of how well a vaccine protects under real-world conditions.
- Eradication: Permanent worldwide reduction of natural disease transmission to zero.
- Elimination: Reduction of disease transmission to a defined target within a particular geographic area.
- Cold chain: Temperature-controlled system used to store and transport vaccines.
Key Takeaways
- Vaccines prepare the adaptive immune system before future exposure to a pathogen.
- Vaccines expose the immune system to antigens or instructions for producing antigens.
- Specific B and T lymphocytes are activated during the vaccine response.
- Activated lymphocytes undergo clonal expansion.
- Plasma cells produce antibodies.
- T cells can coordinate immune responses and help target infected cells.
- Vaccination produces memory cells.
- Memory cells allow a faster and often stronger response during later exposure.
- Vaccination usually produces artificial active immunity.
- Vaccines can use weakened pathogens, inactivated pathogens, pathogen components, toxoids, viral vectors, or genetic instructions such as mRNA.
- Booster doses can strengthen or restore immune protection.
- Vaccination and treatment are different: vaccination is primarily preventive, while treatment addresses an existing infection or disease.
- Vaccines differ in their ability to prevent infection, transmission, symptoms, and severe disease.
- No vaccine necessarily provides complete protection to every individual.
- Herd immunity occurs when population immunity makes sustained transmission more difficult.
- Community immunity can indirectly protect people who remain susceptible.
- The amount of population immunity required depends on the disease, vaccine, and patterns of contact.
- Vaccination programs can reduce disease, complications, hospitalizations, and deaths.
- Vaccination was central to the global eradication of smallpox.
- Maintaining vaccination coverage is important because diseases can return when susceptible populations accumulate.
- Vaccine safety and effectiveness continue to be monitored after vaccines are introduced.
- Access, logistics, cost, misinformation, and public trust can affect vaccination programs.
- Vaccination is an important example of using knowledge of adaptive immunity and immune memory to prevent infectious disease.