Malaria prevention works in Tanzania.

Giving infants regular doses of medicine preempts malaria in the short term, but experience has shown that the children become particularly vulnerable to the illness once they stop taking the drugs. A new study finds that giving a common antimalarial drug to babies only intermittently during their first year works better. While getting the drug, the infants resist the bloodborne parasites that cause the illness, and the children don't appear as vulnerable later.

Scientists working in a part of southern Tanzania that's rife with malaria gave 332 infants a tablet of sulphadoxine-pyrimethamine --crushed and mixed with water--when the babies were 2, 3, and 9 months old. The team gave 329 others crushed inert tablets. The scientists had randomly assigned the babies to one of the two groups at birth. Of the babies, 77 percent received their three scheduled treatments or placebos.

Only 39 of the drug-treated children contracted malaria during the year. In contrast, 88 of the babies getting placebos were so diagnosed, the scientists report in the May 12 LANCET.

In an earlier study, babies who had received other anti-malarial drugs every week between ages 2 and 11 months subsequently experienced a striking increase in malaria.

In a new study, the researchers visited the children at ages 12, 15, and 18 months. The youngsters showed no marked susceptibility to malaria during their second year of life even though they were no longer getting the drug, says study coauthor David Schellenberg of the Hospital Clinic of Barcelona.

This indicates that the babies had built some immunity against the disease during the intermittent dosing, Schellenberg says. The researchers now suggest that health authorities should consider giving sulphadoxine-pyrimethamine as a preventive against malaria.