Download clinical-evidence-brief

Clinical evidence brief
Immunisation
3. National immunisation program
Immunisation is the process of obtaining
‘immune status’ through vaccination.
To ensure immunisation rates remain at a high
level, Australia has a comprehensive National
Immunisation Program (NIP). The NIP Schedule
includes 16 vaccines for mass childhood
immunisation programs and influenza and
Hepatitis A for at-risk adults.
1. Public health benefits
The public health benefits of immunisation
include:
• reduction in illness, disability and death
• control, prevention and eradication
of disease
• protection of both the individual and the
community from vaccine preventable
diseases (VPD)
• a cost effective health strategy.
2. Herd immunity
Herd immunity is the effect achieved when
a significant portion of a population is
vaccinated providing a measure of protection
for individuals who do not have immunity.
Only a small fraction of the population can
be left unvaccinated for this method to be
effective. Unvaccinated individuals may
include those who cannot safely receive
vaccines for various reasons such as impaired
immunity, failure to respond adequately to
vaccination, or egg allergies.1,2
The control of highly infectious diseases,
such as measles, requires 95% of the
population to be vaccinated to prevent the
transmission of the disease. Diphtheria,
a less infectious disease, requires a lower
percentage of the population to be vaccinated
and as a result there have been no cases of
diphtheria in Australia since the 1970s. The
pneumococcal vaccine which was introduced
to protect children against diseases caused
by the bacterium, Streptococcus pneumoniae,
has also been shown to provide protection for
susceptible unvaccinated elderly people due
to a reduction in circulation of the bacterium
in the community.3
3. Vaccines4,5
Vaccines contain active components such as
attenuated live viruses, inactivated viruses,
modified or partial forms of the virus or
bacteria or the toxin produced by the bacteria.
The antigen in the vaccine is altered from its
original form so it no longer causes disease but
produces an immune response.
Active components used in a vaccine are:
• Live viruses used in vaccines are weakened
(or attenuated) limiting the virus’ ability to
replicate and are able to induce an immune
response without causing severe disease.
The advantage of live, attenuated vaccines
is that only one or two doses usually provide
whole of life immunity. However, these
vaccines cannot be given to people with
severely impaired immunity, as a greatly
weakened immune system may not be able
to limit reproduction of the vaccine virus.
Women receiving live viral vaccines must
be advised against falling pregnant within
28 days of vaccination.
• Inactivated viruses are inactivated by
formaldehyde so the pathogenic effects
are rendered inactive but the antigenicity
is preserved. The virus is incapable of
replication after vaccination but it is still
recognised by the body’s immune system.
These vaccines can be given to people with
impaired immunity. Several doses may need
to be given to achieve long-term immunity,
and persons with impaired immunity may
not respond to even multiple doses.
• Part of the virus or bacteria is used in
certain vaccines to induce immunity
e.g. hepatitis B vaccine is composed of
a protein from the surface of the virus,
haemophilus influenzae type b (Hib) vaccine
2013
only the outer coating or polysaccharide
is used and joined to a protein so that
the immune system responds to it.
These vaccines can be administered to
people with weakened immunity, although,
if the person’s immune system is too
weak, they may not develop a satisfactory
immune response.
• Toxins produced by the bacteria are
chemically inactivated to produce
a vaccine that is known as a toxoid.
E.g. diphtheria and tetanus-containing
vaccines. Tetanus vaccination stimulates
the production of antitoxin, which protects
against the toxin produced by the organism.
Having tetanus infection does not induce
a long‑term immune response and nonimmune individuals who contract tetanus
must be fully vaccinated to protect against
future exposure.
References
1 National Prescribing Service. Why be vaccinated. At: www.
nps.org.au/medicines/immune-system/vaccines-andimmunisation/for-individuals/why-be-vaccinated
2 Understanding childhood immunisation booklet (revised June
2010). Immunise Australia Program. At: www.immunise.health.
gov.au/internet/immunise/publishing.nsf/Content/IMM52-cnt
3 The Science of immunisation. Australian Academy of Science
November 2012. At: www.science.org.au/policy/documents/
AAS_Immunisation_FINAL_LR_v3.pdf
4 The Australian Immunisation Handbook 9th Edition. At: www.
health.gov.au/internet/immunise/publishing.nsf/Content/
Handbook-home
5 Vaccine and its Components Fact Sheet. National Council for
Immunisation Research and Surveillance. At: www.ncirs.edu.au/
immunisation/fact-sheets/vaccine-components-fact-sheet.pdf
Practice points
These practice points are taken from the
Immunisation inPHARMation, Facts Behind the
Fact Card article.
Discussing childhood
immunisation with parents4,12
It has been estimated that immunisation
currently saves three million lives per year
throughout the world while remaining one of
the most cost effective health interventions.
When immunisation rates in the community
are very high the number of cases of certain
diseases can be reduced. For example,
Haemophilus influenzae type b (Hib) vaccine
was introduced into the Australian NIP
schedule for all children in 1993. In 1992,
there were 560 cases of Hib disease notified
but in 2006, only 22 cases were notified.
Despite a very good record of effectiveness
and safety, there are still people who have
reservations about immunisation.
To make informed decisions, parents need
to understand the benefits and risks of
vaccination, or not vaccinating, their children.
Parents do not usually understand how
immunisation protects the child, and the
diseases are often not seen as serious.
When discussing concerns about
immunisation with parents or adults,
it is important to recognise that a logical
demonstration of the weaknesses in
arguments against immunisation needs to
be combined with listening and other good
communication skills.
Two useful resources to assist pharmacists in
discussing immunisation issues with parents
are Immunisation Myths & Realities, A Guide
for Providers and Understanding childhood
immunisation, accessible at www.immunise.
health.gov.au
Onset, extent and duration of
immunity2
Immunity does not occur immediately
after vaccination. Activation of the normal
immune response takes approximately two
weeks. Many vaccines require several booster
doses to be given for full immune response
to occur and, even when all the doses of
a vaccine have been given, not everyone
will be immune. Measles, mumps, rubella,
tetanus, polio, hepatitis B and Hib vaccines
protect more than 95% of children who have
completed the recommended immunisation
course. Three doses of whooping cough
vaccine will protect about 85% of children
immunised, and will reduce the severity of
the disease in the other 15% of children if
they do catch whooping cough. One dose
of meningococcal C vaccine at 12 months of
age will protect more than 90% of children
immunised.1,8
The protective effect of immunisation
is not always lifelong. Some vaccines,
such as tetanus, can last up to 30 years,
then a booster dose may be required.
(Note: A booster dose may be required
earlier (e.g. after 10 years) in the presence
of a tetanus prone wound.) Other vaccines,
such as whooping cough, give protection
for about five years after a full course.1,8
A two‑dose course of hepatitis A vaccine
given 6–12 months apart is thought to give
protection for about 20 years.1,2
Contraindications to vaccines 2,8
There are only two absolute contraindications
applicable to all vaccines:
• a known anaphylactic sensitivity to any
component of the relevant vaccine
• anaphylaxis following a previous dose of
the relevant vaccine.
Further contraindications to live attenuated
vaccines are:
• immunosuppressed people regardless
of whether the suppression is caused by
disease or treatment
• adults treated with systemic
corticosteroids in excess of 60 mg of
prednisolone (or equivalent) per day
(vaccination should be postponed until
at least three months after treatment
has stopped)
• pregnancy.
For further explanation, see the Australian
Immunisation Handbook 9th edition.
If a child has an acute febrile illness (current
temperature ≥ 38.5°C) the vaccination should
be postponed for 2–3 days until the child
is well.
The following are NOT contraindications to
any of the vaccines in the NIP Schedule:
• family history of any adverse events
following immunisation
• family history of convulsions
• previous pertussis-like illness, measles,
rubella, mumps or meningococcal infection
• prematurity (vaccination should not
be postponed)
• neurological conditions including cerebral
palsy and Down’s syndrome
• contact with an infectious disease
• asthma, eczema, atopy, hayfever or ‘snuffles’
• treatment with antibiotics
• treatment with locally acting (inhaled or
low-dose topical) steroids
• child’s mother is pregnant
• child to be vaccinated is being breastfed
• woman to be vaccinated is breastfeeding
• history of neonatal jaundice
• low weight in an otherwise healthy child
• recent or imminent surgery.
Late adverse effects of vaccines2
Long term surveillance of vaccines is
conducted to ensure unanticipated adverse
effects are detected. Through the systematic
collection of data and analysis of reports,
some vaccines have been shown to cause
serious late events, although the rate is always
hundreds to thousands times less frequent
than the disease complication. For example:
• Approximately one in 1,000,000 doses
of MMR vaccine among children causes
acute encephalitis occurring 8–9 days after
vaccination. In comparison, one in 500 cases
of naturally-acquired measles results in
severe acute encephalitis.5
• Vaccines containing diphtheria and tetanus
have been implicated in causing brachial
neuritis with an incidence of approximately
one in 100,000 (adults).
• One additional case of Guillain-Barre
syndrome has been detected in every one
million people vaccinated against influenza.5
Although late adverse effects have been
reported following immunisation, there is
strong epidemiological evidence that there is
no causal association between:
• sudden infant death syndrome (SIDS) and
any vaccine
• autism and MMR vaccine
• multiple sclerosis and hepatitis B vaccine
• inflammatory bowel disease (IBD) and MMR
vaccine
• diabetes and Hib vaccine
• asthma and any vaccine.
Practice points
Seasonal influenza vaccines normally contain
three strains of virus; two current influenza
A subtypes, H1N1 and H3N2, and influenza
B, representing recently circulating viruses.
The H1N1 influenza A strain (known as swine
‘flu) is incorporated in the 2013 seasonal
influenza vaccines. However, the current
influenza vaccines will not give protection
against the H5N1 (avian) virus.
Although seasonal influenza vaccines contain
minimal amounts of egg protein, they can
be used in certain egg-sensitive individuals.
Referral to a specialist immunologist is
recommended in such cases, however.5,6
It is important that people in at-risk groups
continue to have annual influenza vaccines.
If a child under the age of nine years is
receiving the vaccine for the first time,
they will require two doses at least one
month apart.2
Vaccination is best given in autumn;
however, it can be given as early as February.
Influenza vaccine can be administered
concurrently with other vaccines, including
pneumococcal polysaccharide vaccine and
all the scheduled childhood vaccines.
Annual influenza vaccination is
recommended for the following groups:13
• all people aged 65 years and older
• Aboriginal and Torres Strait Islander
people over 15 years of age
• children (≥ six months of age) and adults
with chronic illnesses including:
• heart conditions
• lung/respiratory conditions including
asthma
• diabetes (and other chronic metabolic
diseases)
• kidney disease
• impaired immunity
• chronic neurological conditions
including multiple sclerosis and seizure
disorders
• haemoglobinopathies (a range of
genetically inherited disorders of red
blood cell haemoglobin)
• pregnant women
• residents of nursing homes and other
long-term care facilities.
In addition, it is important that people who
care for, or who are in close contact with,
people who are at particular risk, also avoid
spreading the infection. Annual influenza
vaccination is also strongly recommended
for travellers and people providing essential
community services.
The National Health and Medical Research
Council (NHMRC) also recommends that
influenza vaccination can be given to
any person aged 6 months or more who
wishes to reduce the chance of becoming ill
with influenza.
Influenza vaccination should be delayed when
a person has a high fever or a moderately
severe illness, but can generally be given once
the illness is resolved.
Avian flu14
There are many different subtypes of type
A influenza viruses. Influenza A viruses are
constantly changing, and it is possible for
viruses that infect birds to adapt over time to
infect and spread among humans. Influenza A
(H5N1) virus is a highly pathogenic influenza
A virus subtype that occurs mainly in birds.
It does not usually infect people, but about
160 human cases have been reported by the
World Health Organization since January
2004. Most of these cases have occurred
as a result of people having direct or close
contact with infected poultry or contaminated
surfaces. So far, the spread of H5N1 virus from
person‑to‑person has been rare and has not
continued beyond one person.
There is currently no commercially available
vaccine to protect humans against the H5N1
virus that is emerging in Asia and Europe.
However, vaccines are being developed.
Studies to test a vaccine to protect humans
against H5N1 virus began in April 2005, and
a series of clinical trials is in progress. As a
pandemic vaccine needs to be a close match
to the actual pandemic virus, commercial
production cannot begin prior to emergence
and characterisation of the pandemic virus.
On current trends, it appears likely that most
developing countries will have no access to a
vaccine during the first wave of a pandemic
and perhaps throughout its duration.
PSA4007
Seasonal influenza vaccine3