WCS39 Immunization Flashcards
HK Childhood Immunisation Program
Recent changes:
- MMRV vaccine (2nd dose): P1 —> 18 months
- 9-valent HPV vaccine (1st, 2nd dose): P5, P6
Vaccines NOT in HK universal programme:
- ***Haemophilus influenza type b vaccine (very low incidence in HK)
- ***Rotavirus vaccine (no deaths)
Vaccines in HK:
- BCG vaccine
- Hep B vaccine
- DTaP-IPV (Diphtheria, Tetanus, acellular Pertussis, Inactivated Poliovirus) vaccine
- Pneumococcal vaccine
- MMRV (新加Varicella) vaccine
- HPV vaccine (female)
(Mumps (腮腺炎)
Measles (麻疹)
Rubella (風疹, 德國麻疹)
Varicella (水痘))
Immunisation
Active: Antigen (whole / component)
- long-lasting response
Passive: Immunoglobulins (e.g. Zoster Ig, Hep B Ig)
- immune response last ***< few months
Vaccine types
- Live attenuated organism
- OPV, **BCG, **Chickenpox, ***MMR
- exception: Inborn errors of immunity (cannot give live attenuated) - Killed whole organism
- whole cell Pertussis, ***IPV, HAV - Inactivated exotoxin
- **diphtheria toxoid, **tetanus toxoid - Subunit
- acellular Pertussis, pneumovax - Subunit conjugated (e.g. with protein —> make it more immunogenic)
- **Haemophilus influenzae type B, **pneumococcal vaccine: PCV7, PCV10, PCV13
Live attenuated vaccines
- Attenuated (weakened) form of “wild” virus / bacteria
- ***Must replicate to be effective
- Immune response ~ natural infection
Disadvantage:
- Severe reactions possible (e.g. with babies with Inborn errors of immunity)
- ***Interference from circulating Ab (↓ replication of live attenuated organism)
- Unstable
Antibody and Live vaccines
Product given first
- Vaccine: wait 2 weeks before giving Ab
- Antibody: wait >3 months before giving vaccine
(E.g. Kawasaki Ab: high dose needed: 9 months separate from other vaccines)
Inactivated vaccines
- Cannot replicate
- ***Minimal interference from circulating Ab (∴ no need separate from IVIG)
Disadvantages:
- Generally not as effective as live vaccines
- Generally ***3-5 doses
- Immune response mostly ***humoral (may have some T cell response)
- Ab titre fall over time
Vaccination and Immunisation
Can have vaccination but no immunisation
- if host did not mount immune response to vaccine
- e.g. outdated vaccines
Primary vaccine failure: No response to vaccine at all
Secondary vaccine failure: have a response but lose it
Immunological challenges for new vaccines
Ability to generate memory B + T cells in host immune system
Vaccines
- Haemophilus influenzae type b vaccine
- Chickenpox vaccine (introduced in mid-2014)
- Rotavirus vaccine
- Influenza
- Pneumococcal vaccine
Barriers to overcome for universal Hib vaccination
- ***Disease burden low in
- Hong Kong (incidence of Hib meningitis <5 yo: 3 per 100,000)
- Singapore
- Korea
- China - Cost of vaccines
- Haemophilus influenzae type b vaccine
- Relatively low disease prevalence in East Asia
- Conjugate Hib vaccine effective
- Risk-benefit ratio for individual infant is overwhelming for vaccination
- Issue of universal vaccination in HK not settled
- ONLY used in ***private sector in HK with 50% coverage
—> Hib disease incidence already dropped to <1 per 100,000 under 5 yo
- Chickenpox vaccine (introduced in mid-2014)
- Composition: ***Live virus (Oka-Merck strain)
- Efficacy: 95% (65-100%)
- Duration of immunity: > 7 years
- Schedule:
1st dose: **1 year old
2nd dose booster: **18 months, introduced because of waning immunity
Varicella
Varicella epidemiology
- Reservoir: Human
- Transmission: Airborne droplet, Direct contact with lesions
- Temporal pattern: Peak in ***winter and Early spring (US)
- Communicability: 1-2 days before —> 4-5 days after onset of rash (may be longer in immunocompromised)
Pathogenesis:
Respiratory transmission of virus
—> Replication in **nasopharynx and regional LN
—> Repeated episodes of **viraemia (Primary, Secondary, etc.)
—> **Multiple tissues (e.g. skin), including **sensory ganglia, infected during viraemia
—> **Crops of rashes (with various stages: 四代同堂)
—> Red —> **Vesicles —> Crusting
Varicella complications:
- Bacterial infection of lesions
- CNS manifestations (***Reye’s syndrome, Cerebellar ataxia)
- Pneumonia (rare in children)
- Death ~1 in 60,000
Groups at ↑ risk of complications of Varicella:
- ***Normal adults (without prior chicken pox)
- Immunocompromised person
- Newborns with maternal rash onset within ***5 days before —> 48 hours after delivery
- Ig not yet developed in mother even mother has viraemia
Congenital Varicella Syndrome:
- Result from maternal infection during pregnancy
- Period of risk may extend through first 20 weeks to pregnancy
- Atrophy of extremity with skin scarring, low birth weight, eye and neurologic abnormalities
- Risk ~2%
Zoster following vaccination
- Most cases in children
- Risk from ***wild virus 4-5 times higher than from vaccine virus
- Mild illness without complications
- Rotavirus vaccine
Surface antigen
- VP4 neutralisation antigen
- VP7 neutralisation antigen
- 1st gen live RV in late 1990’s linked with intussusception after licensure
- 2nd gen live RV, necessary to do phase III trial
- RV vaccines are safe and efficacious (but only in industrialised, middle income countries)
- Not used in HK, most children manage diarrhoea very well —> minor morbidity
- Influenza vaccine
Recommended group:
- Children 6-23 months (reduce deaths / hospitalisation)
- Children 2-5 yo (reduce hospitalistion)
- Pregnant women (reduce severity)
- Elderly persons (>=65) in residential care homes
- Long-stay residents of institutions for the disabled
- Elderly >=65
- Persons with chronic illness
- Health care workers
- Poultry worker (prevent flu to spread among animal and human)
Challenges in vaccination in healthy children:
- Influenza does not carry high mortality
- only childhood vaccine that requires annual re-vaccination
- uncertain time interval between vaccine availability and influenza starts to circulate
- School Outreach Vaccination in HK from 2019/2020 for all primary schools and kindergartens
- Pneumococcal vaccine
Over 92 different serotypes of pneumococci
Clinical diseases:
- ***Meningitis (serotypes 10A, 15B, 19F, 23F)
- ***Empyema (serotypes 1, 3, 5, 7F, 8, 19A)
- ***Necrotising pneumonia (serotypes 3)
- Septic shock
Efficacy (Not very good):
- 8% against clinical pneumonia
- 36% against CXR-positive pneumonia
- Serotypes 3 in PCV13 vaccine is not effective —> no reduction in IPD (invasive pneumococcal disease)
PCV13 additional serotypes (比其他疫苗多左3, 19A, 6A serotype) cause significant disease burden even with vaccination
Mechanism:
Immunisation
—> Immunogenic response (Vaccine type specific Ab (***IgG))
—> Direct protection against Colonisation (e.g. Nasopharynx) + Disease
Pneumococcal disease and vaccine
- Heavy disease burden
- PCV10 ~ efficacy to PCV13
- 2+1 (2 priming dose + 1 booster) or 3+0 schedule —> similar impact
- serotype replacement and vaccine failure (***serotype 3)
—> need to add other previously non-covered serotype - surveillance of IPD (with ***serotype testing) is a MUST before and after PCV vaccination
Major barrier for using PCV is ***vaccine price
COVID
Characteristics:
- ↓ Type 1 IFN
- ↑ TNF-α, IL-1/6/18
- Lymphopenia indicator of disease severity
- SARS Ab and memory B are short lived (<1 year)
- ***Intranasal route may be better for COVID vaccine
Evolution of immunisation program and prominence of vaccine safety
Prevaccine —> Increasing coverage —> Loss of confidence due to adverse effects of vaccine —> Outbreak —> Resumption of confidence —> Eradication —> Vaccinations can be stopped
