Researchers quantify the risk of children suffering severe outcomes from malaria

Reviewed by Emily Henderson, B.Sc.Sep 15 2021

For the first time in more than two decades, a team from the KEMRI-Wellcome Trust Research Programme and University of Oxford have quantified the risk of children suffering severe outcomes from malaria. They found:

• reducing malaria transmission by a quarter will halve the rate of children needing emergency care for severe, life-threating malaria.
• Tens of thousands of children are admitted every year to hospital with severe malaria. These findings can have a significant impact on many thousands of young children.
• The research supports current intervention policies - focusing on younger children - as the most effective strategy for preventing severe malaria disease.
• By understanding and predicting the age-pattern at which children are hospitalised under different settings, resources can be focused on the children with the highest risk of needing emergency care.

The research, published in Science, analysed over 6000 paediatric hospital admissions from 35 hospitals across each Africa, matching patients to populations where the chances of childhood infection varied from very low to very high. They looked for typical indicators of severe disease in children, including anaemia, cerebral symptoms, and respiratory distress.

The Wellcome-funded study represents the first quantitative analysis of the relationship between community infection risks and admission rates with malaria for over 25 years. The authors report that when transmission is low, fewer than one child in every thousand will need to seek emergency care; this rose to 3-4 children in every thousand under high transmission. By quantifying the rate at which children are hospitalised under different transmission settings, the research allows hospitals to anticipate demand for paediatric emergency care using measures of community parasite exposure.

Across Africa tens of thousands of children are admitted every year to hospital with severe malaria posing a heavy burden on the health system. Our findings support continued our efforts to reduce the infection risks in children under five years of age rather than worrying this would delay the development of immunity."

Dr Alice Kamau, Kenya Medical Research Institute-Wellcome collaboration in Kenya, and co-first author

Reductions in transmission will likely delay first exposure to malaria into later childhood. It had been feared that exposure later in life would deny children the opportunity to develop immunity under the protection of inherited maternal antibodies, which decay after birth. This could have led to more severe outcomes for children as transmission is reduced.

Fortunately, while the study found that admitted children tended to be older in areas of lower transmission, this was significantly offset by far lower overall rates of admission with severe malaria. In areas of higher infection risk, the burden of admissions was concentrated in children under two, highlighting the impact of naturally acquired immunity to severe, life-threatening disease.

Across all types of community malaria risk, malaria admissions were relatively uncommon after the fifth birthday confirming that targeting the under-fives remains the best strategy for preventing severe disease.

'There have been concerns that with a reduction in malaria transmission through intervention would lead to a delayed immunity, shifting the malaria burden into older age groups. Our data show that the age of severe malaria is shifted to older age groups with declining transmission intensity. Despite this shift to older children in lower transmission settings, the overall severe malaria burden remains very low and severe malaria remains predominantly a problem of children below five years of age.' says Senior author Professor Bob Snow from the Kenya Medical Research Institute-Wellcome-Oxford University collaboration in Kenya,

Understanding and predicting changes in the age-pattern of disease burden is important to ensure age-targeted control focused on those with the highest risk of developing clinical disease. Crucially, the work supports the continuation of targeted infection prevention strategies with the aim of preventing life threatening disease among young children.

"Quantifying the relationship between infection risk and severe disease outcomes allows us to better formulate intervention policies that are targeted in the right areas, protect the most vulnerable age groups and maximize limited resources", says Dr Rob Paton, from the University of Oxford, co-first author.

The authors are continuing their collaboration, moving on to conduct further analyses of paediatric malaria admissions in the region.