'Imperfect' Vaccines Risk Worse Disease
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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