High Adherence to Seasonal Malaria Drugs Fails to Show Clear Protection in Nigerian Children

Seasonal malaria chemoprevention, known widely as SMC, has become one of the most ambitious preventive interventions in modern tropical medicine. The strategy involves administering monthly courses of antimalarial drugs to young children during the months of peak malaria transmission, when rainfall and humidity drive mosquito populations to their highest densities. In principle, the approach protects the most vulnerable age group during the most dangerous weeks of the year. A new community-based study from Ogbomoso, in Oyo State, Nigeria, has now examined how well this intervention actually performs under real-world conditions, and the results offer a nuanced picture that is more complicated than the simple success story many might expect.

The research, conducted by a team from Ladoke Akintola University of Technology and partner institutions and published in BMC Infectious Diseases, enrolled 1,257 children aged between 3 and 59 months across four Local Government Areas of Ogbomoso. Of these, 804 children came from communities where SMC had been implemented over two annual cycles, while 453 children were recruited from comparison communities where the programme had not been rolled out. The study was designed as a comparative, cross-sectional post-intervention investigation, meaning that researchers measured both drug adherence and malaria infection status at a single point in time after the intervention had been delivered, rather than following children prospectively through the transmission season.

One of the most striking findings concerns adherence itself. The researchers verified whether children had completed the full SMC regimen using caregiver-held SMC cards, and they found that 96.8 percent of children in the SMC communities had adhered to the complete course of treatment. This figure is remarkably high and suggests that the delivery machinery of the programme, from community health workers to caregivers, functioned well in this setting. When the team examined which socio-demographic factors influenced adherence, only caregiver education emerged as statistically significant, with a p-value of 0.031. This hints that even in a programme with near-universal uptake, the household’s educational background may shape how faithfully the monthly drug courses are administered.

The diagnostic approach of the study deserves particular attention because it reveals how much the choice of laboratory method can shape conclusions in malaria research. All children were screened using malaria rapid diagnostic tests, or mRDTs, which detect parasite antigens in a finger-prick blood sample within minutes. A subset of samples was then subjected to polymerase chain reaction, or PCR, a molecular technique that amplifies parasite DNA and can detect infections at far lower parasite densities than antigen-based tests. Rapid diagnostic tests returned prevalence figures of 16.8 percent in SMC communities and 15.2 percent in non-SMC communities, a difference that was not statistically significant. PCR, by contrast, detected malaria infection in 9.5 percent of children in SMC communities compared with 5.7 percent in non-SMC communities, a difference that reached statistical significance with a p-value of 0.0236.

At first glance, the PCR result might appear alarming, suggesting that children in drug-protected communities carried more parasites than those outside the programme. But the authors were careful to interrogate this apparent paradox. When they adjusted for measured individual-level and study-level covariates in multivariable logistic regression, the difference between SMC and non-SMC communities was attenuated and no longer held. The researchers also flagged a fundamental design limitation: because SMC implementation aligned exactly with Local Government Area boundaries, the exposed and comparison groups were recruited from geographically distinct areas. Residual community-level confounding, in which unmeasured differences between LGAs such as ecology, housing quality, or health service access drive the observed differences, cannot be ruled out despite statistical adjustment. The authors explicitly state that these findings should not be interpreted as evidence of a causal relationship between SMC exposure and malaria positivity.

This methodological caution matters enormously for how the study should be read by policymakers. Cross-sectional comparisons between communities that differ in ways beyond the intervention itself are vulnerable to confounding, and the geographic separation of the groups makes it impossible to fully disentangle the effect of SMC from the effect of place. The higher crude PCR prevalence in SMC communities may reflect underlying population differences rather than any biological effect of the drugs. The authors suggest that the findings highlight the need for continued surveillance and complementary malaria control measures alongside SMC, rather than casting doubt on the intervention itself, which has strong evidence from randomized trials in other settings.

Within the study population, one factor did emerge as a robust and independent predictor of infection. Children aged 37 to 59 months had significantly higher adjusted odds of malaria infection than infants younger than 12 months, with an odds ratio of 2.47 and a 95 percent confidence interval of 1.33 to 4.60, corresponding to a p-value of 0.004. This age gradient is biologically plausible. Infants are partially protected by maternal antibodies transferred across the placenta and, in many settings, by the relative protection of being carried close to their mothers, reducing exposure to biting mosquitoes. As children grow, become more mobile, and spend more time outdoors, their exposure to infected vectors increases while maternally derived immunity wanes, producing a window of heightened vulnerability in the toddler and preschool years.

The relationship between adherence and infection status was examined in both directions, and the results were suggestive but inconclusive. Children who tested positive by either rapid diagnostic test or PCR had higher odds of non-adherence to the SMC regimen, which would fit the intuitive expectation that children who miss doses are less protected. However, these associations did not reach statistical significance, likely because adherence was so uniformly high that too few children fell into the non-adherent category to provide the statistical power needed to detect a difference. With 96.8 percent of children completing the full regimen, the study effectively had very little variation in the exposure of interest, a phenomenon that researchers describe as a restriction of range problem.

The broader context of this work is Nigeria’s position as the country bearing the largest burden of malaria in the world, with young children accounting for the overwhelming majority of deaths. Seasonal malaria chemoprevention, recommended by the World Health Organization for areas of highly seasonal transmission, typically combines sulfadoxine-pyrimethamine with amodiaquine, abbreviated as SP and AQ, delivered across consecutive monthly cycles during the rainy season. The strategy has demonstrated large protective effects in trial settings across the Sahel, but translating trial efficacy into programme effectiveness depends on coverage, adherence, drug quality, and the intensity of ongoing transmission. Studies like this one, which measure what actually happens in communities after implementation cycles, are essential for understanding where the gaps between promise and performance lie.

Ultimately, the study delivers two messages simultaneously. The first is encouraging: a community-based SMC programme in southwestern Nigeria achieved near-complete adherence among its target population, demonstrating that caregivers and health systems can deliver a complex, multi-cycle preventive regimen at scale. The second is a call for humility and continued investment: even with high adherence, malaria infection remained detectable in a meaningful fraction of children, and the observational design could not cleanly attribute differences in infection to the intervention. The authors’ insistence that their findings may reflect underlying population differences, rather than a failure of SMC, underscores a central lesson of implementation science. Preventive tools work best not in isolation but as part of layered strategies that include insecticide-treated nets, environmental management, prompt diagnosis and treatment, and vigilant surveillance capable of detecting shifts in both parasite prevalence and drug effectiveness over time.

Subject of Research: Adherence to seasonal malaria chemoprevention and malaria positivity among children under five in Nigeria

Article Title: Adherence to seasonal malaria chemoprevention and malaria positivity among under-five children in Ogbomoso, Oyo State, Nigeria

Article References: Adherence to seasonal malaria chemoprevention and malaria positivity among under-five children in Ogbomoso, Oyo State, Nigeria. (n.d.). https://doi.org/10.1186/s12879-026-14577-9

Image Credits: AI Generated

DOI: 10.1186/s12879-026-14577-9

Keywords: malaria, seasonal malaria chemoprevention, SMC adherence, under-five children, Nigeria, Oyo State, rapid diagnostic test, PCR, cross-sectional study, public health, tropical medicine, parasitology