Vaccination of infants works best in high transmission areas, the study found

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The most promising malaria vaccine candidate should be rolled out through mass vaccination campaigns — rather than the WHO's routine infant vaccinations — in parts of Africa with low malaria transmission, says a study.

Researchers used computer simulations to predict the health benefits of introducing the RTS,S/AS01 vaccine through different deployment programmes in a range of transmission settings. The vaccine is in Phase 3 trials and could be approved by WHO as early as 2015.

They found that vaccination of infants and schoolchildren through the WHO's Expanded Program on Immunization would work well in areas with high transmission, which includes much of rural Africa.

But in low transmission areas, which are increasingly common in Africa — especially in cities — and also in South America and South-East Asia, mass vaccination may be much more effective, they reported in PLoS Medicine last week (17 January).

This is because in areas with high transmission rates, malaria mostly affects very young children; but in areas with low transmission, all age groups are affected, and so an infant-focused vaccination would miss most of the cases, the paper says.

So far research has focused on high transmission areas, and this is also where vaccine trials take place. For this reason the impact of the vaccine in low transmission areas has been highly uncertain, the paper says.

"We made varying assumptions about the intensity of malaria transmission at the beginning of the vaccination programme and the duration of protection offered by the vaccine against the background of a health system similar to the one in Tanzania," Nicolas Maire, a co-author of the study and project leader for scientific computing at the Swiss Tropical and Public Health Institute, Basel, Switzerland, told SciDev.Net.

The researchers used 'ensemble modelling' that included 14 individual models to simulate transmission of the Plasmodium falciparum parasite, and say it is the first time this technique has been used to analyse the impact of a malaria vaccine.

This approach enables greater accuracy because a wider range of parameters can be included into simulations, the researchers said.

Peter Gething, a researcher at the University of Oxford, United Kingdom, said: "What emerges is that the level of underlying transmission is absolutely key — what works best in one place won't necessarily be optimal elsewhere."

"This is where detailed maps like those from the Malaria Atlas Project can come in to help plan strategies for targeting the vaccine roll-out," he added.

Last month (21 December) Gething and his team published a new malaria map in Malaria Journal. The map reveals "for the first time the startling variations in malaria risk, even over short distances", according to a press release.

Julia Nunes, a programme officer for the PATH Malaria Vaccine Initiative, United States, told SciDev.Net: "The model-generated estimates could be used at the global level to assist in understanding how best to use the vaccine, anticipate demand, and secure appropriate financing".

Link to full paper in PLoS Medicine

Link to full paper in Malaria Journal   [7.59MB]