This analysis used malaria case data from Vietnam’s national Electronic Case-based Disease Surveillance—Malaria and Mosquito-borne Diseases Reporting System covering January 2023 through December 2025. Cases were confirmed by standard microscopy and molecular assays targeting parasite 18S rRNA. Statistical analyses included negative binomial regression with Tukey-adjusted pairwise comparisons; incidence rate ratios (IRRs) and 95% CIs were calculated and p<0.05 was considered significant.
Across the three-year period, 493 symptomatic malaria cases were identified and laboratory-confirmed. Malaria incidence was low before 2023 (3 cases in 2021 and 12 in 2022) but rose sharply in 2023, peaking in July 2023 with the emergence of Plasmodium malariae.
Annual totals were 209 cases in 2023, 199 in 2024, and 85 in 2025. Species-level distribution over 2023–2025 showed P. malariae accounted for 44.8% (n = 221) of cases, P. falciparum for 36.9% (n = 182), P. vivax for 17.9% (n = 88), and mixed infections were rare (0.4%; n = 2). Three-species co-endemicity (P. malariae, P. falciparum, P. vivax) was observed in 2023–2024; in 2025 only P. malariae and P. falciparum were prevalent.
Notably, molecular testing confirmed that all P. malariae cases in the province were monoinfections, despite prior reports from other settings that P. malariae frequently occurs as part of mixed infections.
Khanh Vinh district accounted for 93.1% (n = 459) of all provincial malaria cases; the remaining districts and cities each reported fewer than 15 cases over the study period.
Within Khanh Vinh district, species distributions and counts changed across years. In 2023, P. malariae was the most frequent (104 cases), followed by P. vivax (62) and P. falciparum (29). Geographic overlap of all three species occurred in six communes, including Khanh Thuong and Lien Sang. Other communes had single-species findings (either P. falciparum or P. malariae).
In 2024, P. falciparum cases increased in some communes (for example, Khanh Dong [n = 53] and Khanh Phu [n = 23]) and distribution expanded. Overall P. malariae cases decreased to 72 (IRR 1.444; 95% CI 0.750–2.782; p = 0.272), with large declines in some localities (e.g., Son Thai: 34 cases in 2023 to 3 in 2024) but continued presence in most communes. P. vivax cases decreased markedly to 22 in 2024 (IRR 2.818; 95% CI 2.156–3.685; p<0.001) and had a more restricted geographic distribution.
By 2025, total cases in Khanh Vinh district declined to 77. P. vivax was not detected in the district that year. P. falciparum (n = 41) and P. malariae (n = 36) continued to show geographic overlap in five communes. Overall, the district experienced a gradual decline in case numbers and contraction of endemic areas over the three years, while P. malariae endemicity persisted alongside other species.
Among case-patients in Khanh Vinh district, 338 were male and 121 female (male:female ratio 2.8:1). Most patients were older than 15 years (n = 344; 75.0%). Ethnic distribution showed the Raglai community was disproportionately affected (304 cases; 66.2%), followed by the Kinh (53; 11.6%) and Co Ho (50; 10.9%).
Occupational and exposure characteristics indicated most affected persons were forest-goers (n = 314; 68.4%), with additional cases among rangers (n = 29; 6.3%) and government or factory workers (n = 15; 3.3%). The authors note that heavy dependence on the forest or forest farming for subsistence increases exposure risk for the Raglai population and that the Raglai account for most malaria cases in Central Vietnam in prior reports. The study found no meaningful association between demographic variables and infection with specific Plasmodium species.
The proximate cause of the P. malariae outbreak in Khanh Hoa Province, particularly in Khanh Vinh district, is not established in the source. The authors propose hypotheses without definitive attribution: successful interventions that reduced P. falciparum and P. vivax transmission could have altered ecological niches and facilitated expansion of P. malariae. The source also notes an increase in P. malariae infections detected in 2022 (10 of 12 total malaria cases that year), suggesting the species may have started to emerge before 2023.
The source text ends mid-sentence when discussing the potential earlier emergence of P. malariae and does not report further details, mechanisms, entomologic data, or genetic analyses that might explain the outbreak. Those additional data were not provided in the article text available here.
Between 2023 and 2025, Khanh Hoa Province experienced a marked change in malaria epidemiology with the emergence and persistence of Plasmodium malariae alongside P. falciparum and P. vivax. The outbreak was concentrated in Khanh Vinh district and primarily affected adult males and members of the Raglai ethnic group who engage in forest-related activities.
Given the changing species composition and continued transmission, the authors emphasise the need for strengthened surveillance in the region to monitor species distribution, detect shifts in endemicity, and inform targeted control measures. The source does not provide specific operational recommendations, entomologic findings, or further causal evidence; those details were not reported in the source material provided.