CH 11: Vaccines

What is vaccination

Deliberate delivery of pathogen antigens that can trigger a primary immune response with little or no disease risk

What is the purpose of vaccination

To generate long-lasting immunological memory

Why does vaccination protect against future infection

The immune system responds with a faster and stronger memory response when it later sees the real pathogen

What kind of immune response does a vaccine first produce

A primary immune response

What kind of response happens after a vaccinated person encounters the real pathogen

A secondary or memory immune response

Why is the memory response better than a primary response

It is faster acting and more effective

What was the first medically prescribed vaccine

The smallpox vaccine

What disease was globally eradicated by vaccination

Smallpox

When was smallpox globally eradicated

1979

What was variolation

Immunization using dried material from a mild smallpox pustule

What virus was used for smallpox vaccination in the early 19th century

Cowpox virus

Why could cowpox protect against smallpox

Cowpox and smallpox share some similar surface antigens

What virus was later used in the smallpox vaccine

Vaccinia virus

What is a live-attenuated vaccine

A vaccine containing a live pathogen that has been weakened so it has reduced disease-causing ability

What does attenuated mean

Weakened or reduced in virulence

Can live-attenuated vaccines infect cells and replicate

Yes they can infect cells and replicate in the body

Why do live-attenuated vaccines usually produce strong memory

They mimic natural infection and activate many parts of the immune response

Which vaccine type typically produces the strongest immunological memory

Live-attenuated vaccines

Why do live-attenuated vaccines mimic natural infection best

The weakened pathogen can still infect cells and replicate like the natural pathogen

Are live-attenuated vaccines more common for viral or bacterial vaccines

They are more common for viral vaccines

What is the only bacterial live-attenuated vaccine mentioned

BCG vaccine for Mycobacterium tuberculosis

Is BCG routinely given in the United States

No it is not routinely given in the US

How have many live-attenuated vaccines been made historically

By growing the pathogen in cells from another species

How does growing a pathogen in non-human cells attenuate it

The pathogen adapts to the other species cells and becomes less able to grow in human cells

What happens to pathogenicity after attenuation

Pathogenicity in human cells decreases

What is another way live-attenuated vaccines can be made

A related non-pathogenic strain can be genetically modified to express proteins from the human pathogen

What is a killed or inactivated vaccine

A vaccine containing a whole pathogen that has been killed or inactivated

Can killed or inactivated vaccines replicate in the body

No they cannot replicate

Can killed or inactivated vaccines cause infection

No they cannot cause infection because the pathogen is inactivated

How are killed or inactivated vaccines produced

The whole pathogen is inactivated by chemical or physical treatment

Do killed or inactivated vaccines still trigger immune responses

Yes they still provide pathogen antigens for a primary immune response

Why do killed or inactivated vaccines usually produce weaker memory than live-attenuated vaccines

They do not mimic natural infection as well because they cannot replicate

What is a subunit vaccine

A vaccine containing selected pathogen antigens instead of a whole microbe

Do subunit vaccines contain whole microbes

No they contain only selected antigens

Can subunit vaccine antigens replicate in the body

No they cannot replicate

Why are subunit vaccines safer in terms of infection risk

They do not contain a whole live pathogen

What do subunit vaccines include

Antigens that best stimulate the immune system

Give an example of a subunit vaccine

Hepatitis B vaccine

What antigen does the Hepatitis B vaccine deliver

HBV surface antigen

Give another example of a subunit vaccine

TDaP vaccine

What does the TDaP vaccine deliver

Purified tetanus toxoid diphtheria toxoid and Bordetella pertussis antigens

Give another example of a subunit vaccine

HPV vaccine

What does the HPV vaccine deliver

Viral capsid proteins

What do some COVID vaccines deliver

Viral spike protein or mRNA encoding spike protein

What type of vaccine is an mRNA COVID vaccine considered in this class

Subunit vaccine

What is an adjuvant

A substance added to a vaccine to stimulate the innate immune system

Why might subunit vaccines need an adjuvant

The purified antigen may not contain PAMPs to activate innate immunity

What does an adjuvant help activate

The innate immune response

Why is innate immune activation important for vaccination

It helps activate dendritic cells and start a strong adaptive immune response

What are PAMPs

Pathogen-associated molecular patterns that stimulate innate immune receptors

What are PRRs

Pattern recognition receptors that bind PAMPs

Why do dendritic cells need innate stimulation

They upregulate co-stimulatory molecules and MHC needed to activate T cells

What may happen if a purified antigen lacks PAMPs

It may not activate the innate immune system strongly enough

What does an adjuvant mimic or provide

PAMP-like stimulation or microbial components

What is a toxoid vaccine

A vaccine containing an inactivated toxin that can trigger immunity without toxin disease

What toxin is targeted by the tetanus vaccine

C tetani toxin

If tetanus vaccine is given alone what may be added

A chemical adjuvant

In TDaP what can provide adjuvant-like stimulation

Bordetella pertussis antigens

Which vaccine type contains an attenuated pathogen

Live-attenuated vaccine

Which vaccine type contains a whole but killed pathogen

Killed or inactivated vaccine

Which vaccine type contains only certain antigens

Subunit vaccine

Which vaccine types cannot infect cells and replicate

Killed or inactivated vaccines and subunit vaccines

Which vaccine type can infect cells and replicate

Live-attenuated vaccine

Which vaccine type may rarely cause disease in immunocompromised people

Some live-attenuated vaccines

Which vaccine type generally produces the strongest memory

Live-attenuated vaccine

Which vaccine types can cause side effects from immune response

Live-attenuated killed or inactivated and subunit vaccines

Why can any vaccine cause fever or soreness

Because all vaccines trigger an immune response

Which vaccine type may require an adjuvant

Subunit vaccine

Main difference between live-attenuated and killed vaccines

Live-attenuated vaccines can replicate while killed vaccines cannot

Main difference between killed and subunit vaccines

Killed vaccines contain a whole inactivated pathogen while subunit vaccines contain only selected antigens

Main difference between live-attenuated and subunit vaccines

Live-attenuated vaccines contain a weakened whole pathogen while subunit vaccines contain only selected antigens

Why are live-attenuated vaccines not always preferred

They may rarely cause disease in vulnerable people and can have safety concerns

What are the two polio vaccine types

Live-attenuated oral polio vaccine and inactivated polio vaccine

What does the inactivated polio vaccine protect against

Paralysis

What does the inactivated polio vaccine not fully prevent

Intestinal infection and person-to-person transmission

What does the oral live-attenuated polio vaccine prevent

Infection and person-to-person transmission

What is the rare risk of oral live-attenuated polio vaccine

The attenuated virus can rarely mutate back to a pathogenic form

Where is live-attenuated polio vaccine recommended

In countries where infection risk remains high

Where is inactivated polio vaccine preferred

In low-risk countries

Why must polio vaccine choice balance benefits and drawbacks

Live vaccine blocks transmission better but has rare reversion risk while inactivated vaccine is safer but does not stop transmission as well

What is a conjugate vaccine

A vaccine where a carbohydrate antigen is linked to a protein antigen

Why are conjugate vaccines important for infants

Infants have weak TI-2 responses to repetitive carbohydrate antigens

What are TI-2 antigens

Thymus-independent type 2 antigens such as repetitive bacterial capsular carbohydrates

Do infants produce strong TI-2 responses to encapsulated bacteria

No infants produce weak TI-2 responses

Why are bacterial capsules difficult for infants to respond to

They are repetitive carbohydrate structures that normally trigger weak infant TI-2 responses

What would happen if an infant received only capsular carbohydrate antigen

It would not generate strong protective antibody memory

How does a conjugate vaccine solve weak infant TI-2 responses

It links the carbohydrate to a protein so B cells can receive T-cell help

What concept explains how conjugate vaccines work

Linked recognition

What does linked recognition mean in conjugate vaccines

A B cell binds the carbohydrate but presents protein peptides to a helper T cell

What type of response does a conjugate vaccine create

A thymus-dependent B-2 response to a carbohydrate antigen

What does the B cell receptor bind in a conjugate vaccine

The capsular carbohydrate antigen

What does the B cell present after taking up the conjugate vaccine

Peptides from the linked protein antigen

Which cell provides activating help in a conjugate vaccine

A helper T cell

What does the helper T cell signal cause in conjugate vaccines

B cells produce antibodies and memory against the carbohydrate antigen

What antibody specificity results from a conjugate vaccine

Antibodies specific to the capsular carbohydrate antigen

Give an example of a conjugate vaccine

H influenzae vaccine

Give another example of a conjugate vaccine

N meningitidis vaccine

What is herd immunity

A large majority of immune individuals protects a small minority of non-immune individuals

How does herd immunity protect non-immune people

It lowers the chance they encounter an infected person

How does herd immunity affect chains of infection

It disrupts chains of transmission