By Helen Pearson
Inadequate vaccines can encourage the emergence of nastier bugs, placing the unprotected at risk, a new mathematical model shows. The effect could undermine future vaccination programs.
Many vaccines save people from dying of a disease, but do not stop them carrying and transmitting it. Over a few decades this may cause more virulent strains to evolve, predict Andrew Read and his colleagues of the University of Edinburgh, UK(1).
In some situations, such as in areas endemic for malaria, deadlier disease strains could kill more people than vaccination saves. Most of the time the benefits of vaccination will be eroded.
Vaccines for HIV, and hepatitis B and C "give most cause for concern", says immunologist Charles Bangham, of Imperial College in London. These viruses are difficult for the body's immune system to eradicate, leaving them time to reproduce and evolve. Tearaway strains of flu also emerge regularly and evade existing vaccines.
Infections that linger in the body are more likely to meet a second bug, explains evolutionary biologist Dieter Ebert from the University of Fribourg in Switzerland. The competition drives pathogens to evolve faster, nastier killing tactics to get the most from their host.
Don't Encourage Them
Vaccines that encourage evolution include those that slow a disease-causing organism's growth or target its harmful toxin. These types are being pursued to fight diseases such as anthrax and malaria. The possibility that these might save individuals but harm populations "has not been considered before", says Ebert, and should be a factor in public-health policy.
Most existing vaccines, such as those for smallpox, polio and measles, are very effective as they use a different strategy. They stimulate a natural immune reaction which either kills off subsequent infections or blocks pathogen reproduction and transmission altogether.
Read does not advocate halting such programs. New vaccines should similarly aim to prevent pathogens getting a toehold, says Bangham; many in the pipeline do not.
Several different vaccines are being developed to fight malaria: results of clinical trials for one that interrupts the life cycle of microorganism Plasmodium falciparum were announced last week(2). 'Multivalent vaccines' that target several different parts of a pathogen or life cycle at once are the better choice, Read suggests.
Nature December 13, 2001
Many people will not realize that Nature is one of the most prestigious scientific journals in the world. I point that out to highlight the fact that the concern with vaccines is actually starting to be voiced by some well respected scientists.
Additional Comment from Dawn Richardson of PROVE:
Being healthy becomes an even more elusive goal if you primarily rely on vaccines to get there. When you read this article, keep in mind that children now receive as many as 39 doses of vaccines for 12 different viral and bacterial illnesses and there are literally hundreds of new vaccines in development.
It is also interesting to keep in mind that the bacteria strains chosen for inclusion in the pnuemococcal vaccine for children were specifically chosen because they are the strains that have evolved to be the most antibiotic resistant. It is very difficult to do fair and comprehensive risk/benefit analysis when there is so much about the unintended consequences of vaccines that have yet to even be studied.
More is not better - educated parents everywhere will continue to demand having options for their individual children and the legal right to exercise those options.
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