Practical Vaccinology

PRACTICAL SKILLS IN THE PUBLIC HEALTH

MANAGEMENT OF INFECTIOUS DISEASES (PHPC3015)
Chris Ka Pun Mok

Assistant Professor
The Jockey Club School of Public Health and Primary Care
Bacillus Calmette–Guérin

Diphtheria, Tetanus, acellular Pertussis

& Inactivated Poliovirus Vaccine

MMRV
Measles (麻疹)
Mumps (流行性腮腺炎)
Rubella (德國麻疹)
Varicella (水痘)

Human Papillomavirus
Evidence of the power of vaccine
The use of vaccine was the turning point to control COVID-19 pandemic

COVID-19 vaccines
-What is vaccine?

-Why do we need vaccine?

-How does vaccine function?

-How many types of vaccines?

-Pros and Cons of vaccination?

-How do we justify the performance of vaccine?

Consequence after infection

Immunity Immunity Immunity

-Immunity is induced after infection

 Host defense in human

Immunity
Adaptive
Macrophages, Neutrophils
Innate immune

Innate Immunity
cells
 Why do we still need vaccine?
Measles (1:12-18)
Smallpox (death rate:30%) Polio virus

Some pathogens are too lethal Some pathogens cause serious long-term
effect after recovery
Some pathogens are too transmissible

If we can induce immunity before infection or

quick enough after infection:
-Prevention of infection
-Reduce the disease severity (hospitalization)
-Reduce the chance of death
 What is vaccine?

-A vaccine is a biological product that can be used to safely induce an immune

response that provides protection against infection or disease on subsequent
exposure to a pathogen.

-Killed/Weaken/Component/Fragment pathogen

-Our body still regards them as “foreigners”

-Mimic similar defense as infection

-Develop immunity against the corresponding pathogen

-Do not cause uncontrollable harm or damage to the recipients

 How does vaccine function? First step: Recognition

Pathogen

Our immune system

Self or non-self?
 Dendritic Cell

Dendritic Cell

-having a branched form resembling a tree -Antigen Presentation: A process that dendritic celsl
-live under the skin or organs show different parts of the pathogen to our immune
-Professional presenter cells
 How does the vaccine work? (1)

Activate B cell response

Antigen presentation

-T cell will verify this is a component of a pathogen

Antibody (Immunoglobulin)
-Y-shaped protein

-Recognizes a unique molecule on the pathogen, called an antigen

-One antibody only recognize one type of antigen (Specificity)

-Pathogen is inactivated if the antibodies bind on the surface antigen

-This process is called “Neutralization”; To prevent infection

Immunoglobulin Classes

IgA, IgG and IgM are used against infection

IgM is the first type of antibody to be produced during

first infection. But the neutralizing affinity is lower.

IgG has the highest neutralizing affinity produce slowly

during the first infection but produce quickly during the
re-infection

IgA is produced temporally at the infection site to

prevent the next infection
 How does the vaccine work? (2)

Helper T cell Cytotoxic T cell

“Neutralization” “Cytotoxicity”
 Functions of vaccine

1.B cells >>> Antibody >>> Neutralization

2.T cells >>> Perforin/Granzymes >>> Cytotoxicity

 Infection vs Vaccination

During Infection:

Innate immunity

3-6 Months

However,
During Vaccination: No pathogen is replicating………..No strong innate immunity is triggered
The Missing Link

Adjuvant: Aluminum salt

Induces innate immunity
and cheats our immune
system to respond
**Not every vaccine requires adjuvant; Use or
not use adjuvant, depend on the antigen

DTaP-IPV
Combined Diphtheria, Tetanus, acellular
Pertussis and Inactivated Poliovirus Vaccine
Vaccine is still not strong enough even with adjuvant
Memory B and T cells

-Memory B and T cells form after

first vaccination
-Stay in the blood, spleen and
bone marrow
-Reactivated when infected by the
same pathogen

Protect the host from reinfection

Most of the vaccines need more than 1 dose
Second vaccination,
Strong and quick respond from memory

First vaccination,
Weak and slow response
No memory

Question: We only take one dose of Flu vaccine

Why?
How to determine the performance of vaccine?

Preclinical trial

Vaccine

Weight loss
Death
Replication

-Large quantity -Symptoms are similar to human

-Easy to handle -Measure the protection and safety
-Outcome is obvious
How to determine the performance of vaccine?
Clinical Trial
 From Laboratory to licensure

Phase IV

Sometimes it may take over 10 years!!!!

Vaccine coverage, Virus transmission (R0) and herd immunity

How do we achieve this?

Vaccine coverage = 1- (1/R0)

Pollard and Bijker, 2021, Nature Reviews
How does vaccine benefit us?
-individual Correlate of Protection (CoP)
-community
-Antibody that provides protection to infection

Method 1 Method 2

-Human challenge experiment after vaccination -Compare the antibody level between those are
infected and uninfected in the population

Measure the antibody level

-It is impossible to justify the performance of a vaccine by testing the antibody of everybody
-Variation among individuals
Effect of antibody waning, memory and protection from infection

Scenario 1 Scenario 3
vaccination infection vaccination

Scenario 2
vaccination infection

Pollard and Bijker, 2021, Nature Reviews

How to determine the performance of vaccine?

Vaccine efficacy

WHO website
Types of vaccine

Live pathogen

Killed pathogen

Pathogen component

Pathogen Genome
Live attenuated vaccine
-Using similar pathogen from other animals or a weaken pathogen
-The pathogen still has a slower or weaker replication
-Mimic the infection and trigger immune response
-Immunity can be long-lasting

Example 1: Smallpox vaccine

-Cowpox, first vaccine to prevent smallpox
-Reduced case-fatality rate from 25% to 1%

Example 2: TB vaccine
-BCG (Bacillus Calmette–Guérin), prevent tuberculosis
-Bacteria naturally causing tuberculosis in cattle

-Side effects in infant, elderly or patients with chronic disease

 What is Tuberculosis? Gram-negative, rod shape bacteria
1 Replicate very slow

2 Airborne

Mycobacterium. Tuberculosis

3
 BCG (Bacillus Calmette–Guérin) vaccine 卡介苗
-Contains live bovine (cow) tuberculosis bacillus that have been
weakened

-1952: United Nations International Children‘s Emergency Fund and

WHO sponsored HK a 3 years BCG vaccination program

Stage 1: School Children; Non-compulsory

Stage 2: Adults >15 years old; 94% were positive to the pre-
vaccination test

Stage 3: School Children (collaborated with Schools) + New-born

(collaborated with hospitals)

-1961: 79.3% of new-born received BCG vaccine; <5 years old: TB

death rate dropped 73%, TB meningitis dropped 68% (vs 1952)
Example 3: Cold adaptive influenza vaccine (CAIV)

-Developed in 1960s
-Cold adaptive means the influenza viruses are engineered and only grow effectively at “Cold” temperature (25 oC vs 37oC)
-Intranasal administration
-Advantage: 1) Provide good immune response 2) Non-transmissible 3) No needle
-Disadvantage: People with immunosuppression cannot be used
-The pathogen is killed but keep the integrity
-Formaldehyde (“Fixation”), pH, Temperature, Radiation

Advantage:
-More stable and safe

Disadvantage:
-Reduced immune response
-The pathogen need to be grown manually
-Need large facilities to grow the pathogen

Example 1: Rabies vaccine

-Aimed to attenuate the virus as rabies vaccine
-Dry the affected nerve tissue from rabbit
-The first man-made inactivated virus
-Use after infection (virus goes to brain slowly)

Example 2: Polio vaccine

-Inactivated Polio vaccine for prevent polio virus
-Need three doses
 Attenuated or Inactivated?
Albert Sabin Jonas Salk
Inactivated poliovirus vaccine (IPV) (1955)

-Very effective. By 1957, annual cases dropped from

58000 to 5600, and by 1961, only 161 cases remained.
-Expensive
-Safe

Live attenuated oral poliovirus vaccine (OPV) (1959)

-A candy form, easy to administer

-Effective OPV
-Cheap (15cent vs >1 dollar)
-Strong mucosal (intestinal) immunity, better protection Current situation:
-The vaccine (virus) can transmit by close contact so
that it can provide passively vaccinate others -Most of the countries use IPV
-Some countries still use OPV
-Causing paralytic disease in rare cases (Vaccine- -Fractional dose IPV is testing
associated paralytic poliomyelitis VAPP) in poor countries
-Mutation occurs and become virulence virus
(circulating Vaccine-Derived Polioviruses cVDPVs)
-Exotoxin is produced by bacteria to cause disease
-Toxoid means that the exotoxin is inactivated by chemical or heat
-The inactivated exotoxin still can induce immune response by not
toxic anymore
-Diphtheria (白喉), Tetanus (破傷風), Pertussis (百日咳)

Concept
-Antibody target to the surface protein of virus
through “Neutralization”

-Produce and purify the surface antigen as

vaccine

Hepatitis A/B vaccine:

Inactivated for Hep A
Subunit for Hep B
Hepatitis A viruses
-Food and water borne disease
-Cause gastrointestinal disease

Hepatitis B viruses
-Transmitted by blood or body fluid
-Infect Liver and cause liver cirrhosis and liver
cancer
 -Virus-like particle means virus with the coat but no genomic
material inside
-Borrow yeast as the host to produce the coat of the virus
Strains that most likely cause cancer

-HPV vaccine for protect Human papillomavirus (人類乳頭狀瘤病毒)

-Infect into cell, integrate its DNA into human cell and cause uncontrolled grow
-Can infect women and men
-HPV can cause Cervical (F), Penile (M), Anal and Oropharyngeal cancers (F/M)
-Prevent Warts (疣)
-Children ages 11–12 (2 doses); After 15, (3 doses)
-Not recommended for age >26 years (High +ve)
 -Astrazeneca, COVID-19 ERVEBO, Ebola

Ring vaccination
-Borrow another non-pathogenic virus to express the
targeted viral protein
-Gram-negative bacteria secrets Outer Member Vesicle (OMV)
-The OMV carries specific antigen of the bacteria
-These OMVs are immunogenic and can be used as vaccine

-Group B Meningococcal vaccine (乙型腦膜炎球菌)

-Cause meningitis and sepsis
-Used in infant and children
-Not included in the vaccine program of HK; Low prevalent
-There is a unique type of sugar expressing on the surface of bacteria

-The antigens of bacteria are conjugated with/without link to a protein

-Stimulate both strong T and B cell response

-Pneumococcal vaccine for Streptococcus pneumoniae (肺炎鏈球菌)

-Cause sepsis, meningitis and pneumonia
-There are 94 types but only some are pathogenic

In Hong Kong, two pneumococcal vaccines are used:

1) 23-valent pneumococcal polysaccharide vaccine (23vPPV)

- high risk and >2 years old
- >65 years old

2) 13-valent pneumococcal conjugate vaccines (PCV15)

- <2 years old
DNA/mRNA vaccine
-DNA transcript to RNA, RNA translate to protein
-However, the mRNA needs to be modified to reduce the
immune response
-Negative charge on the DNA/RNA
-Lipid nanoparticle (LNP) can bring the DNA/RNA into the cell
-LNP can be act as an adjuvant

Advantage:
-No need to grow the pathogen
-Express the target antigen only
-Strong immune response

Disadvantage:
-Strong/Unknown side effect
-Need ultra low temperature to keep the vaccine (-80oC)
-The vaccine need to be diluted before use
 Essential accident in vaccine development (1)

-Respiratory syncytial virus (RSV)

-Respiratory virus like flu
-Cause Pneumonia in young children
-58,000 children younger than 5 years old are hospitalized per year

In 1966, a vaccine was tested in the United States against RSV

Tested subjects: Children under 2
RSV subunit vaccine Results: No protection, worse than control after RSV infection,
Two kids died because of enhanced disease symptoms

RSV vaccine development was stopped until recent years……

 Essential accident in vaccine development (2)
Dengue fever
-Dengue virus (4 serotypes)
-Mosquito-borne illness
-Dengue hemorrhagic fever, can cause serious bleeding, a sudden
drop in blood pressure (shock) and death
-Antibody Dependent Enhancement (ADE)>>> Dengue use the
antibody to bring itself into the cell

In April 2016, a clinical trial of Dengvaxia in Philippines

800,000 children was administrated with the vaccine
Several children died; few hundreds suspected deaths
Pose an increased risk of severe dengue illness to those who have
not infected dengue virus before

Vaccination rate of other vaccine dropped from 82% to 21%

Vaccine hesitancy
 Vaccines in our life
Born/Childhood
Travel Health Service

-Cholera vaccine
-Japanese Encephalitis vaccine
-Meningococcal vaccine
-Rabies vaccine
-Typhoid vaccine
-Yellow fever vaccine

On demand
-Influenza vaccine
-COVID-19 vaccine

MMRV
Measles (麻疹)
Mumps (流行性腮腺炎)
Rubella (德國麻疹)
Varicella (水痘) Can you find what types of vaccine are they?
How do we utilize the vaccine…….?
Our impression on the power of vaccine

Vaccination
Infection of SARS-COV-2 even I had received X
doses of COVID-19 vaccine

My symptoms

Fever, Sore Throat, Coughing, Running nose, Headache, Muscle pain

 COVID-19 vaccine

World Economic Forum

It took only less than 1 year…..Why?

 Emergency Use Listing Procedure (EUL)
Fast Track
-A risk-based procedure for assessing and listing the data of the vaccine (quality, safety and performance) which
have not (yet) undergone stringent regulatory assessment

Eligibility

-Public health emergencies of international concern (PHEICs) declared by WHO’s Director-General

-The disease is (likely) causing outbreak/pandemic
-No Licensed product is available
-The product is manufactured under a functional quality management system
-be intended for completion of development (validation and verification) and submission WHO prequalification
-Examples: COVID-19, EBOLA, ZIKA
 Virus Inactivated mRNA

How do we make the choice?

 Two stages of COVID outbreak in Hong Kong
-At the beginning of the outbreak, we knew the infection caused
high mortality, prevalent in HK was low because of the “zero
covid policy” (0.1-0.01%)

-Both mRNA (Biontech) and virus inactivated

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-Original Wuhan Strain (Wild type) was circulating 70
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Conclusion: Biontech trigger higher antibody level than Sinovac
Sinovac showed less side effect after vaccination

BNT162b2 CoronaVac

n 366 360 p-value

Pain at injection site 283 129 <0.001
Fever 111 12 <0.001
Headache 107 47 <0.001
Muscle Pain 193 73 <0.001
Fatigue 237 134 <0.001
Anorexia 33 2 <0.001
Sore throat 9 13 0.394
Cough 6 8 0.601
Stuffy nose 6 5 1
Runny nose 8 15 0.142
Vomiting 0 0 -
Stomach ache 4 4 1
Diarrhoea 20 14 0.381
No complain 23 107 <0.001

People with strong allergic response may not be able to receive Biontech
Other factors:

Stock availability

Facility and manpower for handling

Number of dose required

Storage

Cost
 20
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 Omicron is coming to town~~
-was discovered in S.Africa, Nov2021
-More than 30 amino acid mutation in the spike
-Our vaccine still use the Wuhan strain
Antibody level

Antibody level
The presence of Omicron specific antibody does
not explain everything……
Vaccine efficacy

3 doses of either Biontech and Sionvac reduce the severity of Omicron infection

McMenamin et al, 2022, Lancet ID

Higher antibody level in vaccinated individuals
during breakthrough infection
Memory is playing the
protective role

(Protection threshold)

Cheng et al. JCV, 2022

Vaccinated + Infection
Not vaccinated + Infection
COVID-19 can maintain T cell but not Antibody response to the Omicron

T cell recognizes the unmutated area of the virus

Helper T cell Cytotoxic T cell

-Reduce the disease severity √

-Prevention of infection ×
-Reduce the chance of death √
Data from the HK government
 Conclusion

- When original strain was circulating, high antibody level should be

maintained in the population to reduce infection and transmission

- Although Biontech should be prioritized (High antibody level), Sinovac

can be used for those who cannot receive mRNA vaccine

- In Omicron outbreak, it is known that both vaccines cannot prevent the

infection (Breakthrough).

- Memory immunity and T cell response still can reduce severity and
death to the infection of new variants
 Human influenza vaccine
H3N2
-Inactivated influenza vaccine was licensed for military used in 1945 Flu B
(Thomas Francis Jr and Jonas Salk) H1N1

-Human influenza A H3N2, H1N1 and 2 influenza B are circulating in

the world

-If persons with weakened immunity and elderly persons get infected,
it can be a serious illness and may be complicated by bronchitis,
pneumonia, encephalopathy, or even death in the most serious cases.

-Influenza vaccine has two forms of composition

1) Trivalent (H1, H3, 1 FluB) 2) Quadrivalent (H1, H3, 2 FluB)

-Flu vaccine trigger antibodies against the hemagglutinin (HA)

-They evolve every year to escape the human immunity

(infection/vaccination)

-Influenza vaccine need to be updated every year

Seasonal influenza vaccine in Hong Kong

The Seasonal Influenza Vaccination Subsidy Scheme (VSS)

Three types of influenza vaccines are widely used nowadays

Whole Virus Inactivated Vaccine

- The live viruses are grown in embryonic eggs or vero cells
(Monkey cell line)
- Inactivated by formalin or heating
- High safety profile, maintaining complete viral antigenic
components with high immunogenicity
- Some people have allergy to eggs

Split-Virion Influenza Vaccine

- Modified version of inactivated vaccine
- Using splitting agents and conditions to disrupt the viral
envelope and split open the virion particles Virus-like particle

- RNA, large protein or chemicals are discarded

- Higher concentration of antigens
- Higher purify >> more safe

Live Attenuated Influenza Vaccine

- Cold adapted, replicate in lower temperature (25 oC)
- Given through nasal spray
- Provide strong immunity
- Use in children only
- Safety concern >> mutation
One for Northern Hemisphere and One for Southern Hemisphere

Predict the virus

Prepare vaccine candidates

Inject into the animal to collect sera

Test if the sera can neutralize the virus

Test the candidates

Confirmed by WHO meeting

The whole process take around 6-9 months

 Problems faced by influenza vaccine

- The vaccine candidates need to be confirmed at least 6 months ahead, sometimes the prediction may
be wrong

- The eggs maybe affected by avian influenza outbreak

- HUMAN flu virus may adapt into AVIAN eggs during the production. Reduce the protective effect of the
vaccine

- The scale of producing flu vaccine by cells is still small

- Antibody will drop after vaccination (Recommend to take before the flu season)

- Elderly respond poorly to the flu vaccine (Immunosenescence,免疫老化)

Solution?
 Limitation of vaccine

-Not everyone respond well to the same vaccine

-Virus may evolve
Elderly, Immunocompromised patients….
Influenza virus
Einav G et al, 2021, NEJM

-Side effects
-Antibody waning (Not good for elderly) From pain to Guillain-Barre, Myocarditis
Our Future: 1, 2, 3, 4 or more doses……..

Dreamstime.com
 Universal Vaccine

-Ideally, universal vaccine means one can protect all pathogens

-In reality, we refer to the one that protects against all subtypes within a given pathogen family

-Most of the vaccines target to a specific pathogen only. For example: COVID-19 or Flu vaccine
 How does Universal Vaccine work?

-Normally, different antibodies target to different sites (epitope)

-SARS-CoV-2 infect cell through the binding on spike
between Spike and cell receptor
-Most epitopes are specific to one type of coronavirus
-Antibodies can block the interaction
-However, few sites are similar between different CoVs

-If our vaccine can stimulate these ”Cross-reactive” antibodies,

it can protect different CoVs
Clinical trial of universal vaccine for influenza virus
 Key message

-A vaccine is a biological product that can be used to safely induce an immune response that
confers protection against infection/disease on subsequent exposure to a pathogen.

-Vaccine can achieve: 1) Prevention of infection 2) Reduce the disease severity 3) Reduce the
chance of death

-Vaccine targets to protect individual and community

-Vaccine induce antibody and T cell responses

-There are different type of vaccines (9)

-The performance of vaccine can be justified by correlate of protection and vaccine efficacy

-Selection of vaccine depends on multiple factors

Thank you