Antimalarial Drug Efficacy Remains High in Mozambique and Liberia Despite Regional Resistance Concerns
Key Insights
Two major therapeutic efficacy studies in Mozambique and Liberia demonstrate that artemisinin-based combination therapies maintain high cure rates above 90% WHO thresholds despite emerging resistance concerns in East Africa.
In Mozambique, four antimalarial combinations showed PCR-corrected efficacy rates of 97.6-100%, with artemether-lumefantrine maintaining consistent performance over multiple years of surveillance.
Liberian study results confirm both artemether-lumefantrine and artesunate-amodiaquine (search) remain highly effective with 94-100% cure rates, supporting continued use as first-line treatments.
Two comprehensive therapeutic efficacy studies conducted in Mozambique and Liberia provide reassuring evidence that artemisinin-based combination therapies (ACTs) remain highly effective for treating uncomplicated malaria (search), despite growing concerns about antimalarial resistance emerging in East Africa.
Mozambique Study Demonstrates Sustained ACT Performance
A multi-site study conducted across five sentinel sites in Mozambique from March 2022 to December 2022 evaluated four different ACT regimens in 829 children aged 6-59 months with uncomplicated Plasmodium falciparum (search) malaria (search). The research, following WHO in vivo protocol guidelines, tested artemether-lumefantrine (AL), artesunate-amodiaquine (search) (AS-AQ), dihydroartemisinin-piperaquine (DP), and artesunate-pyronaridine (search) (AS-PY) across three regions with varying malaria transmission intensities.
The PCR-corrected efficacy results exceeded WHO thresholds at all sites. AL demonstrated efficacy rates of 97.6% to 100% across the five locations, maintaining consistency with previous Mozambican studies that showed 94.2-100% efficacy from 2011-2018. AS-AQ achieved 100% efficacy at both tested sites, while DP and AS-PY showed 100% and 97.8% efficacy respectively.
"The findings of previous studies conducted in Mozambique demonstrated that the efficacy of AL has remained constant over time, with a range of 94.2–97.0% PCR-corrected efficacy in 2011–2012, 96.4–100% in 2015, 95.4–100% in 2018 and 97.4–100% in the present study," the researchers reported.
Day 3 parasite positivity rates, a key indicator of potential artemisinin resistance, remained well below the 10% threshold that would suggest partial resistance. Rates ranged from 0% to 2.3% across all treatment arms, lower than some previous studies and indicating no immediate threat to artemisinin effectiveness.
Liberian Results Support Dual First-Line Strategy
In Liberia, researchers conducted a parallel study from August 2022 to July 2023, evaluating AL and AS-AQ in 305 children across two health facilities. This study was particularly significant given that a previous 2017-2018 evaluation had shown declining AS-AQ efficacy, prompting prioritization of AL as the preferred first-line treatment.
The current results showed marked improvement in both treatments. PCR-corrected adequate clinical and parasitological response (ACPR) rates were 100% at the Saclepea site for both AL and AS-AQ. At the Sinje site, AL achieved 95.9% efficacy while AS-AQ reached 94.4% efficacy, both exceeding the 90% WHO threshold.
Only two participants in the AS-AQ arm remained parasitemic on day 3, representing a 1.3% positivity rate that suggests continued artemisinin sensitivity. No adverse events were reported for either treatment during the study period.
Clinical Implications and Safety Profile
Both studies demonstrated excellent safety profiles with minimal adverse events. In Mozambique, reported side effects included mild urticaria (2.6% for AL, 1.1% for AS-AQ), vomiting (1.1% for AL, 2.2% for DP), and diarrhea (0.9-1.6% across treatments). One serious adverse event occurred but was deemed unrelated to study medications.
The studies also tracked hemoglobin recovery, an important indicator of treatment benefit beyond parasite clearance. In Mozambique, mean hemoglobin levels increased from 9.5 g/dl to 9.9 g/dl in the AL arm (p = 0.029), while AS-AQ showed recovery from 9.3 g/dl to 10 g/dl between days 14 and 28 (p = 0.0000).
Resistance Surveillance Remains Critical
Despite these encouraging results, both research teams emphasized the importance of continued surveillance. Recent evidence of partial artemisinin resistance in East Africa underscores the need for routine monitoring in all malaria (search)-endemic countries.
The Mozambique study noted that different transmission intensities and seasonal variations may have influenced reinfection rates between treatment arms. AL and AS-PY showed higher percentages of recurrent parasitemia (1.2-20.2% and 18.2% respectively) compared to AS-AQ and DP (0-5.9% and 2.3%), likely reflecting differences in partner drug half-lives and post-treatment prophylactic effects.
Policy Implications
These findings support current treatment policies in both countries while providing flexibility for future strategies. In Mozambique, the results endorse continued use of AL as first-line treatment and AS-AQ as co-first-line therapy. The high efficacy of DP and AS-PY suggests these could serve as alternative first-line treatments if needed.
For Liberia, the study provides evidence that both AL and AS-AQ remain viable first-line options, potentially allowing for implementation of multiple first-line therapy strategies that could help delay resistance development through treatment rotation or geographic stratification.
The research demonstrates that while antimalarial resistance remains a global concern, targeted surveillance and evidence-based policy adjustments can maintain effective malaria (search) case management in endemic regions.