Study: Some Vaccines Could Do More Harm Than Good
January 3, 2002
The Associated Press
and Agence France-Presse
A new study claims that some future malaria vaccines that donÕt entirely wipe out the disease might unintentionally serve to make it more deadly.
The study, published in the journal Nature, uses mathematical analysis to examine the effect of partially effective, or "imperfect," malaria vaccines.
In some scenarios, the study says, a hypothetical vaccine designed to reduce the growth rate or transmission of the malarial parasite caused it to evolve into a more virulent strain.
"The thrust of our paper is that [parasites] can become more nasty, and certain types of vaccines can promote the nastiness of the disease,"said Andrew Read, a researcher at the Institute of Cell, Animal and Population Biology at the University of Edinburgh in England.
On the other hand, vaccines specifically designed to block infection resulted in less virulent strains.
The researchers examined malaria because it provides a good example of a disease likely to require "imperfect"vaccines, Read said.
"We're now moving into an era of vaccines which deal with diseases where natural immunity isn't that good to begin with,"he said.
"The vaccines aren't going to be that good, and malaria is a classic example of that; the malaria vaccines probably won't be very good,"he said.
Scientists not connected to the study cautioned that it is based on a theoretical model, which uses untested assumptions that may be incorrect. They noted that no human population vaccinated for any disease has shown evidence of what Read's team posits.
"I think of this as adding one more item to the list of things that we should watch for as vaccines are used,"said Dr Marc Lipsitch, an expert in epidemiology at the Harvard School of Public Health.
"It raises a theoretical possibility that many people may not have thought
of before...[but] it's not actually sounding an alarm that something is happening
or is about to happen."
In other malaria news, a Thai software site has launched a downloadable program that it says will keep mosquitoes at bay by emitting a low-frequency sound from computer speakers.
Thaiware.com programmer Saranyou Punyaratabunbhu said his Anti-Mosquitoes Program, which has been downloaded 15,000 times, produces a sound that is inaudible to humans but which hampers the irritating insects' ability to fly.
"Instead of having to plug in extra mosquito-killers, you could just use your computer to drive them away," Saranyou told The Nation newspaper, adding that he was inspired by existing devices that used the same concept.
"You'd just be using your computer for more purposes than normal,"he added.
When a mosquito flies into a zone where low-frequency sounds in the 15 to 20 kiloherz range are being emitted, a sort of ÒturbulenceÓ is created that makes it difficult for them to fly, the report said.
Messages posted on a thaiware.com bulletin board generally gave good reviews of the program, but some users said it caused headaches, particularly at the lower 15 kiloherz level.
"I can tell that there are fewer mosquitoes around, but the program should be developed so that it has fewer side-effects on human beings and the environment," one said. "My dog was lying by the computer and it suddenly began staring at the speakers when I launched the program."
Mosquitoes are more than a headache in Thailand, which suffers high rates of potentially lethal mosquito-borne diseases including malaria and dengue fever.