  The Case for Pneumococcal Vaccination
Invasive pneumococcal disease (IPD) is defined as the isolation of
Streptococcus pneumoniae from a normally sterile site, usually the
blood.1 IPD is the cause of several serious clinical infections that
lead to substantial morbidity and mortality, including pneumonia,
bacteremia without focus and meningitis. IPD is also the leading cause
of meningitis in children aged 5 years of age and under.1 The risk of
infection is greatest in immunocompromised individuals as well as
immunocompetent people with chronic conditions such as cardiovascular
disease, chronic pulmonary disease and diabetes.1,4
The incidence of IPD in Sydney in
1997-1999 was approximately 14 per 100,000 people,
reaching almost 100 per 100,000 in the very young (2
years of age and under) and the very old (85 years
of age and over).1 In some groups of Indigenous
Australians, the rate is as high as 200 per 100,000
people.1 Antibiotic-resistant pneumococci are
becoming prevalent around the world, increasing the
importance of preventive measures such as
vaccination.5 Laboratory surveillance of IPD in
Australia during 2001 and 2002 showed that, of 1,355
isolates from non-Indigenous children, 86% belonged
to serotypes and 93% to serogroups represented in
the 7-valent pneumococcal conjugate vaccine.28
Reduced susceptibility to penicillin and
erythromycin was observed in 13% and 24% of
isolates, respectively.
Types of pneumococcal vaccines
available in Australia
Two types of pneumococcal vaccines
are currently available in Australia: a 23-valent
pneumococcal polysaccharide vaccine (23vPPV) for
older children and adults at risk of IPD; and a
pneumococcal vaccine with 7 capsular polysaccharides
conjugated to mutant non-toxic diphtheria toxin
(7vPCV) for children aged 6 weeks to 9 years. The
23vPPV contains antigens of the 23 most frequent or
virulent serotypes of pneumococci that cause
approximately 90% of bacteraemic pneumococcal
diseases, while the 7vPCV appears to confer at least
73-94% efficacy against IPD due to the serotypes
contained in the vaccine.1,5
Revaccination is often
required after 3-5 years because the pneumococcal
polysaccharide vaccine does not induce immunologic
memory.1,29
Several meta-analyses have assessed
the benefits of pneumococcal vaccination in adults,
including a recent Cochrane systematic review. The
Cochrane review was unable to demonstrate efficacy
of the polysaccharide pneumococcal vaccine against
either all-cause pneumonia or death in adults (with
or without chronic illness).4 Both of these are nonspecific outcomes for which the meta-analysis was
unable to exclude the possibility of a small benefit
from vaccination.
There were not enough cases of IPD
in randomised controlled trials to assess the effect
of vaccination, but case-control studies showed
significant efficacy in preventing IPD in adults and
immunocompetent older people (aged 55 years and
above). Two other systematic reviews of randomised
controlled trials and observational studies reported
similar findings; they showed that vaccination was
efficacious against IPD, but results were not
consistent for protection against all-cause
pneumonia.30,31
Results from other meta-analyses are
conflicting; one analysis found that the
pneumococcal polysaccharide vaccine was effective
against mortality and all-cause pneumonia in
nonindustrialised countries but not in
industrialised nations.32 Some researchers report
that the vaccine is effective against bacteraemic
pneumococcal pneumonia in low-risk healthy adults
but not in those at high risk,33-35 while others
suggest that the vaccine is no less efficacious for
high-risk persons.36
The discrepancies in the findings of
these metaanalyses are essentially related to
variations in the inclusion/exclusion criteria and
to varying interpretations of appropriate subgroups
for a very heterogeneous group of trials.
The efficacy of the pneumococcal
conjugate vaccination against IPD in children has
been more firmly established in randomised
controlled trials. A Cochrane review found that the
vaccination is effective in reducing the incidence
of IPD from all serotypes, and is also effective in
reducing the incidence of radiologically-confirmed
pneumonia (although there are still uncertainties
about the definition of consolidation on X-ray).5
A metaanalysis examining the protection against otitis
media found that pneumococcal conjugate vaccination
in infants and toddlers with recurrent acute otitis
media has only a modest effect on the prevention of
further episodes.37
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