The controversial new malaria vaccine

Health News,  August, 1995  

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The world's "most wanted" safe, effective vaccines include ones against malaria, HIV (the AIDS virus), tuberculosis and - in the developed world - products against respiratory syncytial virus and pneumonia. Transmitted by the bite of an anopheles mosquito, malaria is the world's biggest killer among infectious diseases and on the rise. The World Health Organization (WHO) estimates that 300 to 500 million cases of malaria occur each year, resulting in over two million deaths worldwide. The main risk areas include tropical Africa, S.E. Asia, parts of India, southern China, Latin America, Haiti and some Pacific islands, especially New Guinea and Papua. Malaria is a protozoal infection spread by mosquitoes that feed on human blood usually between dusk and dawn. The incubation period (time from mosquito bite to appearance of symptoms) is 10-60 days but can be longer. The malaria parasites enter the liver where they multiply, then spill out into the circulation in large numbers (invading red blood cells), producing flu-like fevers, chills, headache, muscle aches, fatigue, perhaps vomiting and a cough. Untreated malaria can be fatal. It's diagnosed by detecting the telltale parasites with a special blood test. Of the four types of malarial parasite that attack humans, only Plasmodium falciparum is lethai, and a drug-resistant strain, not treatable by traditional antimalarials, has emerged as a major killer in many tropical countries.

Treatment must be swift to prevent coma and respiratory or kidney failure. The antimalarial drugs used to cure (or prevent) the illness depend on the infecting strains. Forms resistant to chloroquine have emerged in many tropical areas and mefloquine (Lariam) is the drug of choice against chloroquine-resistant malaria. Preventive medication should be taken by anyone visiting malaria-infested areas, starting before departure and continuing for one month after returning. Yet surveys reveal considerable misinformation (even among physicians) about the best antimalarials to take and noncompliance among travellers - many of whom stop taking the drugs too soon or skip doses.

An unorthodox and much-debated synthetic malaria vaccine has recently been developed by a Colombian biochemist and physician, Dr. Manuel Patarroyo. Named Spf66 by its originators at the Immunology Institute in Bogota, this vaccine shows some preventive action against malaria infection, even against drug-resistant falciparum parasites. But when first announced in 1987 few took this vaccine seriously. The scientif ic community exhibited widespread skepticism toward the Colombian vaccine - partly because it originated from research in a small country and because of its unusual manner of preparation. Synthetically crafted from malaria proteins chemically linked together, it was designed to prevent disease by producing antibodies that would inactivate one peptide (protein) in the malaria parasite.

Some of the early skepticism about this vaccine has been dispelled by studies showing that it can protect a certain percentage of those inoculated. The vaccine has been shown to stimulate the immune system's T cells, and the antibodies it induces do recognize real malaria parasites rather than just the vaccine's synthetic peptides. Although many scientists reserve judgement on this vaccine, trials in Colombia and Tanzania show it to have a 30-40 per cent efficacy rate in preventing the disease, especially in children. A large trial in Tanzania found that vaccine shots reduced childhood deaths from P falciparum malaria by about one third. That's an important result, because previously successful trials of the vaccine were conducted in South America, where the rate of malaria is far lower than in the worst affected regions of Africa. Many tropical medical experts had pessimistically expected that the protection offered by the Colombian vaccine would be swamped by the huge numbers of malaria parasites to which Tanzanian children are exposed (averaging 300 mosquito bites a day).

Besides its unusual structure, this vaccine is also remarkable because Dr. Patarroyo willingly forfeited any profits from its commercialization and donated all proceeds to the WHO as a humanitarian gesture. The WHO will decide when it's ready for full-scale production, probably only in a few years.

Experts in the field say it's too early to tell if the vaccine will be a viable weapon against malaria. Some significant unknowns remain. Only one of SPf66's three main antigens has belongs to a "blood-stage" of the malaria parasite, and no one knows if the vaccine can be manufactured reliably in large quantities. Researchers believe it may be necessary to improve Spf66 - perhaps by incorporating other antigens into the vaccine- to make it more effective, and also usable for travellers.

The debate over what happens next continues. WHO and many Western public-health officials call for more research. Patarroyo argues that - in the absence of any rival vaccine at a similarly advanced stage of development - it's mandatory to plan further clinical trials. "We have to use whatever weapons we have", For many vaccines, a 30-40 per cent protective efficacy rate (from three vaccine shots) wouldn't be enough to merit widespread use, but even a 30 per cent reduction in the enormous toll of malaria might be worth a try A more effective vaccine may soon emerge that uses some of the Colombian findings but attacks the malaria parasite at different stages of its life cycle.

COPYRIGHT 1995 Strategic Inc. Communications Ltd.
COPYRIGHT 2008 Gale, Cengage Learning