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Chapter: Medicine Study Notes : Infectious Diseases


Jenner first vaccinated using cowpox against smallpox in 1796


Vaccination Principles


·        Jenner first vaccinated using cowpox against smallpox in 1796

·        Characteristics of immunity:

o   Specificity: response to specific antigen

o   Priming

o   Memory: brisk secondary response

·        Results of vaccine:

o   Most stimulate serum antibodies (IgG, IgM)

o   Some stimulate IgA (eg polio, rubella)

o   A few promote cell mediated reaction (eg BCG)

·        Types of vaccine: 

o   Live attenuated vaccine (eg OPV, MMR, VZ, BCG): full and long lasting immunity after a single dose (except OPV which requires 3 doses)

o   Inactivated vaccines: 

§  First dose gives a predominantly IgM response. Further doses raise IgG level (depending on potency of the vaccine, maturity of the immune system and time interval) 

§  Inactivated whole bacteria or viral vaccines: IPV, Hep A, Whole cell pertussis (being replaced). 

§  Modified toxins (toxoids) eg Diphtheria, Tetanus ® antibody response to toxin not infective agent 

§  Sub-unit vaccines: eg Hep B, HIB, Pneumococcus, Influenza – the main focus of modern vaccines – conjugated vaccines with fewer side effects and easy to grow from genetically engineered yeasts etc. 

o   Also passive immunity available from injectable IgG. Immediate protection lasting from weeks to months

·        Population protection:

o   Immunisation is delivered to individuals and provides individual protection and benefit

o   Also provides population protection (herd immunity): 

§  Some level of immunisation protects unimmunised people who would otherwise have caught it Þ don‟t need to immunise those for whom its contraindicated (eg too young or sick)

§  ­Virulence Þ ­coverage necessary to get herd immunity 

§  „Free riders‟ – because they perceive costs (needles, hassle, side effects) to be greater than perceived benefits ® weakens herd immunity

·        Efficacy and effectiveness: 

o   Efficacy: Does intervention provide a specific outcome (eg an IgG response) under ideal lab circumstances 

o   Effectiveness: Does it work under normal clinical circumstances 

o   Apparent paradox: as coverage ­, so does the proportion of cases that have been vaccinated (but lower absolute numbers of disease), due to vaccination failure. Can create the illusion that the vaccine is ineffective 

·        Vaccine failure: 

o   Primary vaccine failure: inadequate physiological response to the vaccine (eg freezing or overheating of the vaccine, or poor host response) 

o   Secondary vaccine failure: waning immunity

·        Degrees of protection:

o   Generally provides 80 – 95% protection (BCG 50%, Influenza 70%)

o   May protect against severe disease rather than infection (eg Diphtheria)

·        Vaccination coverage:

o   = Proportion of a population who have completed a specific course of immunisation

o   In Northern Region in 1996, 63% by 2 years but only 45% for Maori and 53% for Pacific islanders 

o   With measles: ­coverage ® ­time between epidemics as need a pool of 130 – 150,000 measles susceptible children to sustain an epidemic. Each epidemic ® 50,000 kids contract measles and therefore immune in future. 10,000 unprotected kids added to the pool each year. 

o   Policy measures: revise schedule to reduce the number of visits, immunisation certificates on enrolment at school/early childhood centre.

·        Surveillance: Generally poor systems 

o   Disease surveillance: notifications, discharge and mortality database, outbreak investigations, disease modelling

·        Coverage surveillance: registers and periodic surveys

·        Adverse event surveillance

·        Cold-chain monitoring


Vaccination Practice


·        Practical vaccination standards: 

o  Ensure correct storage and transport: maintain the „cold chain‟ at 2 – 8 C. Eg have dedicated fridge and check its minimum and maximum temperature daily 

o  Check vaccines due for each patient: either age groups (neonates, children, adolescents, adults, elderly) or specific exposure situations (occupational, travel, post-exposure) 

o  Discuss and obtain informed consent: Written consent only required for children if care giver not present

o  Check contra-indications

o  Administer vaccine

o  Manage adverse reactions:

§  Observe for 20 minutes afterwards 

§  Local or systemic reactions (fever, rash, joint pains): symptoms of immune activation. Offer Paracetamol. Especially whole cell pertussis. MMR may be followed about 7 – 10 days later by a 2 – 3 day fever and rash (but the vaccine is not infectious) 

§  Anaphylaxis: Distinguish from fainting (which is common). Treatment: ABC, Adrenaline

§  1:1000 IM injection, 0.01 ml/kg, O2 

§  Report to centre for Adverse Reaction Monitoring if serious (includes persistent screaming > 3 hours and > 5 cm swelling at injection site), but also convulsions, meningitis within 30 days

o  Manage records: practice notes, HBL claim record and immunisation certificate for parents

·        Anti-immunisation views:

o  Risks outweigh benefits: some diseases now rare and specific vaccines have serious side effects 

o  Alternative health views: disease part of growing up (so was death!) and natural infection develops immune system

o  Plus a variety of beliefs/values that will be hard to shift

o  Main reasons for non-immunisation is „passive rejecters‟ – don‟t get around to it

·        Contraindications:

o  Acute illness or fever > 38 C: defer vaccine.  Otherwise will blame the illness on the vaccine!

o  Living with an immune suppressed person: use IPV rather than OPV 

o  Reaction to previous dose: encephalopathy with 7 days of DTP vaccines or immediate severe allergic reaction. If true anaphylaxis seek specialist advice 

o  Immune suppression: don‟t give live vaccine. Likely to have reduced response to inactivated vaccines 

o  Pregnancy: theoretical risk from live virus vaccines

o  If in doubt, refer to a paediatrician

·        False contraindications:

o  Mild illness, URTI, fever < 38.5 C

o  Asthma, hay fever, eczema

o  Prematurity and low birth weight in an otherwise healthy child – these especially need vaccination 

o  Previous clinical history of illness: no harm done from vaccinating and many clinically diagnosed cases of an illness are in fact something else

o  On antibiotics, inhaled or low dose steroids

o  Stable neurological conditions (cerebral palsy, Down)


Currently Vaccine Schedule


·        Current Vaccination Schedule from February 2002:


o  Covers Hep B, Diphtheria (child dose = D, adult dose = d – smaller), Tetanus, acellular Pertussis, Polio (now all intravenous = IPV, not oral), Hib, Measles, Mumps, Rubella



o   For unimmunised adults:

§  Give jabs over same timeframe

§  Don‟t need HIB, don‟t give paediatric dose of diphtheria (too big) and more inclined to use

§  IPV

·        Additional vaccination in specific age groups:

o   Neonates: 

§  Babies of HBsAg +ive mothers: Hepatitis B immune globulin (HBIG) and vaccine at birth, vaccine at 6 weeks, 3 months and 5 months. Also offer vaccination to household and sexual contacts. 

§  BCG if possible Tb exposure

o   Women of child bearing age who are susceptible to Rubella should be offered MMR

o   Adults: Td (after injury and at 45 and 65 – used to be 10 yearly) + annual influenza

o   Elderly: annual influenza + pneumococcal (5 yearly)

·        Specific exposure situations:

o   Splenectomy: Pneumococcal vaccine

o   Occupational:  Health care workers (eg Hep B) or HAV to food workers

o   Travel:  See Topic: Travel Medicine

·        Future Developments:

o   Inclusion of Varicella Zoster and pneumococcal for children 

o   Research into Group B meningococcal (currently 10 year epidemic, 250 cases per year), Rotavirus and RSV, non-infectious diseases including cancer


Vaccine Preventable Diseases


·        Measles and Pertussis are the main ones still happening that we shouldn‟t have

·        Hepatitis B:   


o  Body fluids (blood, semen), including transfusion & contaminated needles 

o  Mother to baby (vertical transmission): 95% risk of infection – vaccinate at birth and give Anti-HBs – immune globulin

o  Organ transplant 

o  Child to child (horizontal transmission). Must get into blood – e.g. grazes, stubbed toes. Very resilient virus. Children are most likely to have asymptomatic seroconversion


·        Diphtheria: 

o   Corynebacterium diphtheriae ® respiratory and cutaneous infection (grey membrane on throat). Exotoxin causes cardiac toxicity and ascending paralysis. Spread by nasal droplets 

o   1 imported case in last 20 years.  Till 1945 killed 100 babies a year.  High is USSR in 90s.

o   Vaccine: inactivated diphtheria toxoid, boosters every 10 years.  > 80% efficacy

·        Tetanus: 

o   Clostridium tetani from soil and animal faeces ® muscular rigidity due to neurone specific toxin, 10% mortality 

o   3 notifications per year (old ladies in the garden).  Common in environment Þ no herd immunity

o   Vaccine: Inactivated toxoid, boosters every 10 years, 100% efficacy

·        Pertussis:  

·        Bordetella Pertussis = Whooping Cough

·        Treatment: if < 4 weeks duration: erythromycin. Doesn‟t impact illness after paroxysmal phase is established, but will ¯ infectivity

·        Admit if under 6 months and/or cyanosis or apnoea in paroxysms

·        Polio:

o   Enterovirus spread by faeces and saliva

o   Presentation:

§  Usually asymptomatic or mild (fever, headache, nausea, vomiting 

§  Only 1% of infected get severe clinical disease: severe muscle pain, neck and back stiffness ® flaccid paralysis

o   Last wild virus infection in 1962.  Occasional imported and vaccine associated cases

o   Vaccine:

§  Live oral polio (OPV) > 90% protection after 3 doses. < 1% of recipients develop diarrhoea, headache or muscle pains. 1 in 2.5 million recipients or close contacts develop paralysis (more common in immunosuppressed) = Vaccine Associated Polio Paralysis (VAPP) 

§  Inactivated polio vaccine (IPV) for immunocompromised (will be used more widely when it can be combined with other jabs)

·        Haemophilus influenzae type B (HIB):   

·        Caused by Haemophilus Influenza Type B

·        Incidence ~ 20 cases pa (dropped from 160 in 1992 prior to vaccination)

·        Presentation:

o  Incubation for 2 – 4 days

o  Acute, febrile illness, toxic looking child 

o  Snore, mouth always open, drooling, prefers to sit upright. Soft inspiratory stridor, louder expiratory stridor

o  No cough (cf croup)

·        Management:

o  Blood cultures

o  Intubate first, then give iv antibiotics (if given first, pain ® panic ® respiratory arrest) 

o  Cefotaxime 25 – 50 mg/kg/8hr iv (max 2g) due to ­penicillin resistance

o  Amoxycillin 50 mg/kg/4 hr iv (max 2g) if penicillin sensitive

·        Other illnesses caused by H Influenzae type B:

·        Measles:  

·        Highly contagious paramyxovirus spread by coughing and nasal droplets 

·        Treatment: Supportive, antibiotics for 2ndary infection

·        Complications:

o  Otitis media (10%)

o  Pneumonia (1 – 5%) 

o  Encephalitis (0.1%): 15% die and 25% left severely disabled. 1 in 100,000 develop the fatal grey matter degenerative disorder Subacute Sclerosing Panencephalitis (SSPE)

·        Vaccine: 

o  Live attenuated virus. Now MMR2 given at 4 years to ­ time between epidemics and address 2 – 5% chance of primary vaccine failure in first dose 

o  Mild fever, malaise or rash develops in about 1% 7 – 10 days after vaccination

o  1 in 1 million develop encephalitis (1,000 fold less likely than if infected with wild virus)

o  Contraindicated during pregnancy and in immunocompromised hosts 

·        Mumps 

·        Contagious paramyxovirus spread by saliva and droplets

·        ~ 80 notified cases per annum.  Used to be 3 – 4 year epidemics, now longer

·        Presentation:

o  Incubation 2 – 3 weeks

o  70% develop fever and swelling and tenderness of salivary glands

o  15% have aseptic meningitis

o  0.2% develop encephalitis

o  20% of post-pubertal males have painful orchitis

o  Case fatality is 0.02% - usually from encephalitis

·        Infective 1 week before and after parotid swelling starts 

·        Rubella:

o  Togavirus spread by nasal droplets

o  Presentation:

§  Incubation 2 – 3 weeks 

§  Fever, headache, mild conjunctivitis, erythematous maculo-papular rash, lymphadenopathy (especially posterior triangle), arthritis, arthralgia

§  50% develop the rash and lymphadenopathy

§  50% of adolescents and adults have arthralgia or even frank arthritis

§  1 in 5,000 have encephalitis

o  Complications:

§  Congenital rubella syndrome: 90% of embryos of mothers infected in 1st trimester will abort or have major abnormalities (severely retarded, seizures, deafness, cardiac defects). Frequent problems after birth 

§  Rate of congenital rubella is 5 times the US rate

o  ~ 60 notifications per annum (1600 in 1995)

o  Vaccine:

§  98 % protective 

§  To protect the unborn child only – relies on herd immunity. Need to vaccinate guys as well otherwise they will maintain a population reservoir which women with vaccine failure will catch 

§  5% of adolescents and adults have arthralgia and 1% have non-infectious rash

§  Contra-indicated in pregnancy and immunosuppressed

·        Influenza:

o  Virus types A (H3N2 and H1N1) and B

o  Causes Fever, rigors, headache, myalgia, protraction.  Estimated 400 deaths per annum. 

o  Vaccine: inactivated subunit vaccine for new strains (resulting from „antigenic drift‟). 60 –90% effective. Contraindicated if egg allergy

o  Pandemics result from „antigenic shift‟

·        Tb: BCG:  See Mycobacteria,

·        Pneumococcal Disease:  See Streptococcus Pneumoniae

·        Varicella Zoster: See Infectious Diseases,


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