Vaccines are known to prevent infection but a recent study
shows that when it comes to their protective potential,
we've only just scratched the surface. "[They] can be
a powerful strategy for reducing antibiotic resistance
in a community," observe researchers in a report published
in the March 2 issue of the Lancet. The research
group from Emory University in Atlanta, Georgia, reached
this conclusion while investigating the benefits of a
heptavalent conjugate vaccine against Streptococcus
pneumoniae-mediated invasive pneumoccocal disease
(IPD).
According to Canada's National
Advisory Committee on Immunization (NACI), an average
of 15 children under the age of five die annually due
to S pneumoniae infection. Of course, not only
young children are affected — approximately 2,200
cases of hospitalized pneumonia and 9,000 cases of non-hospitalized
pneumonia are attributed to this microbe every year.
The US Food and Drug Administration
approved the vaccine against this agent in 2000 and
Health Canada followed suit soon after, making it the
first pneumoccocal conjugate vaccine accepted for use
in Canada. Has this move paid off? The answer is a resounding
"yes" — as the recent report indicates, rates of
antibiotic-resistant S pneumoniae infection are
falling due to the introduction of the heptavalent vaccine.
NOT
JUST FOR KIDS
Looking at the period from 1994-2002, the research team
headed by lead author Dr David S Stephens calculated
cumulative incidence rates for IPD using US Census data.
They observed striking results — IPD incidence
rates fell from a mean of 30.2 (1994-99) to 13.1 per
100,000 people in 2002. Among children under two, there
was an 82% decrease in incidence; children between two
and four years saw a 71% drop in infection rates. These
were the groups targeted to receive the vaccine. Significant
benefits were also seen in adults — a 54% drop
in infection rates occurred among those aged 20-39,
rates fell by 25% among those aged 40-64 while those
over 65 saw a drop of 39% in IPD incidence.
Surprisingly, the vaccine has had
an effect even among groups who were not vaccinated,
through a mechanism known as 'herd immunity.' Among
immunized populations, susceptible individuals are less
likely to become infected due to a decreased reservoir
of the infectious agent.
Most interestingly, according to
the authors, was the drop seen in S pneumoniae
antibiotic resistance following introduction of the
vaccine. After having more than doubled from 4.5 to
9.3 between 1994 and 1999, resistance fell to 2.9 per
100,000 people by 2002.
The bacterium is the leading cause
of IPD among young children in Canada. The aboriginal
population appears to be particularly susceptible to
this infectious agent. According to a 2002 NACI report,
among some Canadian aboriginal populations "the overall
incidence was 27 per 100,000" with fatality rates of
9%. "Of the reported cases, 30% were children under
two years." Because this pathogen poses such a serious
health threat, it's fortunate that we have the conjugate
vaccine to add to Canada's disease fighting arsenal.
Lancet Mar 2, 2005;365:855-63
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