http://dailynews.yahoo.com/h/nm/20011212/hl/vaccines_2.html
Wednesday December 12 5:20 PM ET
By Amy Norton
NEW YORK (Reuters Health) - Experimental vaccines that would provide only some
protection against disease could potentially make the public health situation
worse, according to UK researchers.
They urge caution in going ahead with any ``imperfect'' vaccines, such as
those being developed for malaria.
Imperfect vaccines are those that do not completely prevent people from
being infected with a pathogen. For instance, a number of candidate vaccines
for malaria seek to stop the disease parasite from proliferating in the blood
of an infected person, as opposed to blocking infection altogether.
The concern, according to Professor Andrew F. Read of the University of
Edinburgh, is that such vaccines could encourage the evolution of ``nastier''
pathogens that would be even more deadly to unvaccinated people.
He and his colleagues used a mathematical model to look at how, over the
years, imperfect vaccines could aid in the emergence of more virulent
pathogens. They report the findings in the December 13th issue of Nature.
Read cautioned, however, that their report is not meant to create concern
about standard vaccines.
``It is our feeling...that most vaccines in current use are near-perfect,''
he told Reuters Health. But, he explained, this is because these vaccines boost
a person's natural immunity to a given disease.
``What we are concerned about,'' Read said, ``is future generations of
vaccines which will deal with diseases like malaria where even natural immunity
isn't very good.''
His team's mathematical model showed that vaccines designed to halt a
pathogen's spread or reduce its toxicity in the body could eventually spur the
survival of more virulent pathogens. This could, in turn, boost death rates
among people who do get sick--possibly even outweighing the lives saved by
vaccination.
This research, according to Read, points out that there are ''evolutionary
risks'' in giving imperfect vaccines, and that if they are used, public health
experts should closely monitor the virulence of pathogens in the environment.
SOURCE: Nature 2001;414:751-756.
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