Regional and Temporal Dynamics of Dengue in Mexico (2020–2024): A Comprehensive Epidemiological Analysis

ABSTRACT

Dengue remains a major public health concern in Mexico, with incidence and clinical burden increasing substantially in recent years. Using national surveillance data from 2020 to 2024, this study provides a comprehensive overview of the changing epidemiological landscape, with an emphasis on geographic distribution, temporal trends, serotype dynamics, and disease severity. Over this period, Mexico saw an almost fivefold increase in dengue cases, reaching over 123,000 confirmed infections and 426 deaths in 2024, the highest annual number recorded. Seasonal patterns shifted, with sustained transmission extending into unusual winter months from late 2023. Serotyping data revealed a shift in predominant virus serotypes, with DENV2 predominating until 2022, DENV1 peaking in 2021, and DENV3 rising sharply from 2022 onward, becoming dominant in 2023 and almost exclusive by 2024. This shift coincided with a sustained rise in dengue with warning signs (from 16.9% in 2020 to > 42% in 2023–2024) and higher hospitalisation rates, while severe dengue remained below 5%. Although DENV3 dominated nationally, DENV1 and DENV2 persisted in specific states, and DENV4 circulated sporadically, particularly in southern and northern regions. Several traditionally low‐prevalence states experienced atypical outbreaks, underscoring the potential for sudden epidemic expansion. Climatic analysis showed a consistent positive association between temperature and DENV3 prevalence, with precipitation effects varying by year. Odds ratio analysis suggested serotype‐specific differences in severity across years. These findings underscore the heterogeneous and dynamic nature of dengue transmission in Mexico and highlight the need for regional surveillance, prevention, and clinical preparedness strategies.

Abbreviations

ADE

antibody‐dependent enhancement

DENV1

Dengue virus serotype 1

DENV2

Dengue virus serotype 2

DENV3

Dengue virus serotype 3

DENV4

Dengue virus serotype 4

DWoWS

Dengue without warning signs

DWWS

Dengue with warning signs

OR

Odds ratio

SD

severe dengue

WHO

World Health Organisation

1. Introduction

Dengue fever is caused by four different subtypes of dengue virus (DENV1 to DENV4), and this viral infection is transmitted by Aedes spp. Mosquitoes. Dengue fever has various clinical manifestations, from mild febrile illness to severe complications such as dengue haemorrhagic fever and dengue shock syndrome [1]. An infection with a dengue type confers homologous lifetime protection but only temporary cross‐immunity to the other types; moreover, secondary infections with a different dengue type can increase the risk of complications [2].

In the Americas, dengue incidence has increased dramatically over the past few years, reaching an all‐time high in 2024 (https://www.paho.org/en/arbo‐portal/dengue‐data‐and‐analysis). Even more worrisome, DENV outbreaks have recently expanded into temperate zones, suggesting that dengue's geographic range has grown [3, 4]. Reported cases to the WHO increased from over 500,000 in 2000 to 6.5 million in 2023, affecting more than 80 countries and causing over 7300 deaths. However, the actual number of cases is much higher because of widespread underreporting, asymptomatic or mild infections that do not require medical attention, and frequent misdiagnosis [5, 6]. According to modelling studies, around 390 million infections occur yearly, with 96 million exhibiting clinical symptoms, and around 3.9 billion people living in at‐risk areas [4, 7, 8]. Despite recent outbreaks in temperate zones, Southeast Asia and the Americas still hold the largest proportion of the burden.

Numerous social, environmental, and behavioural factors are directly linked to the rising dengue burden [7]. Urban growth, high population density, inadequate water infrastructure, and common household water storage practices contribute to the long‐term mosquito reproduction and transmission [9]. Moreover, risk is influenced by knowledge, attitudes, and practices related to mosquito control and personal protection. Transmission seasons and vector ranges have also been expanded by climate variability, which includes rising temperatures and more precipitation [3]. These factors dynamically interact with the virus and host populations, changing risk patterns and making control measures more difficult.

Mexico exemplifies these trends, where dengue remains a significant public health challenge due to notable increases in incidence and severity. Historical analyses from 2007 to 2020 have shown persistent geographic clustering of dengue morbidity and mortality, with southern and southeastern states consistently reporting the highest burdens and occasional outbreaks extending into traditionally low‐incidence areas [10]. More recent data indicates that there has been a sharp escalation in the national case burden. Confirmed cases reached their highest ever annual total, with 123,148 in 2024 [11]. However, the number is estimated to have exceeded 457,000, because not all suspected cases are sent for a diagnostic test, per surveillance policy. The number of deaths also increased significantly, with 426 fatalities attributable to dengue in 2024. According to early statistics from 2025, this tendency appears to continue, by epidemiological week 10; over 2100 cases had been reported, with over half requiring hospitalisation. Notably, as observed in late 2024, the seasonal distribution of cases has changed, with unprecedented transmission peaks during the winter months.

In addition to its health impact, dengue imposes a considerable economic burden in Mexico, with annual costs estimated in the hundreds of millions of US dollars when accounting for direct medical expenses, loss of productivity, and societal impacts [12, 13]. This economic pressure further emphasises the need for timely detection, targeted prevention, and effective vector control strategies.

Based on national surveillance data, this study provides a comprehensive epidemiological analysis of dengue in Mexico between 2020 and 2024. It explored the geographical and temporal dynamics, regional disparities, and new disease burden trends to characterise dengue circulation patterns and impact in the country.

2. Dengue Data Acquisition and Analysis

Epidemiological data on dengue cases in Mexico from 2020 to 2024 were obtained from the official open‐access repository of the Pan American Health Organisation, available at: https://www.paho.org/en/arbo‐portal/countries/mexico‐country‐profile. This database contains weekly reports of suspected, confirmed, and negative dengue cases, together with comprehensive data on patient demographics, clinical outcomes, and laboratory‐confirmed serotype data.

Mexico's national dengue surveillance employs a tiered laboratory sampling strategy based on clinical classification and local transmission status. In areas without documented dengue circulation, all probable cases undergo laboratory confirmation. Once local transmission is established, sampling is reduced to 30% for dengue without warning signs (DWoWS), while maintaining 100% coverage for dengue with warning signs (DWWS) and severe dengue (SD) [14]. Consequently, laboratory‐confirmed cases represent only a subset of the total disease burden captured through surveillance. To estimate the annual burden beyond laboratory‐confirmed cases, the total number of cases was calculated as: confirmed cases + (positivity × probable cases), where positivity was defined as confirmed/(confirmed + negative). This approach provides a surveillance‐based approximation of the overall dengue burden, acknowledging that not all probable cases are laboratory tested.

Laboratory‐confirmed cases with available subtype information were used to describe serotype circulation over time and across states. Because serotyping was available for only a subset of confirmed cases, serotype distributions should be interpreted as reflecting typed confirmed cases within the surveillance framework rather than the full distribution of all infections. To ensure robust interpretation, only states with an annual number of serotyped cases above the first quartile (Q1) for that year were included in the state‐level analysis.

To assess serotype‐specific differences in disease severity, odds ratios (OR) with 95% confidence intervals were calculated annually by comparing each serotype against all other serotypes within the same year. In the primary analysis, SD cases were compared against all non‐SD cases (DWWS + DWoWS). Because DWoWS cases are sampled less intensively, a sensitivity analysis was additionally performed by restricting comparisons to SD versus DWWS cases. This restricted analysis was used to reduce potential bias arising from differential sampling of non‐severe cases and to provide a more conservative assessment of serotype‐severity patterns.

State‐level dengue serotypes were assembled at the state–year level for 2022–2024 and linked to annual mean temperature (°C) and precipitation (mm). For each stratum, we defined the outcome as DENV3 successes and non‐DENV3 failures (total serotyped cases − DENV3). We fitted binomial GLMs per year with mean temperature and log‐transformed precipitation (log [mm+1]) as predictors and a pooled model with year fixed effects (2022–2024). We report OR per +1°C and per unit increase in log‐precipitation, with Wald 95% CIs and p‐values. Analyses were implemented in Python (statsmodels). Climatic generalised linear models and serotype‐specific severity odds ratios (SD, DWWS) were estimated in Python (statsmodels); data processing and visualisation were performed in R (RStudio 2023.12.1).

3. National Burden, Temporal Trends, and Case Characteristics of Dengue Cases

From 2020 to 2024, Mexico had a significant rise in dengue cases (Figure 1A). The number of cases remained low from 2020 to 2022, with monthly totals rarely surpassing 5000 nationwide. However, a marked shift occurred in 2023; probable cases rose from 26,145 in 2022 to 170,060, and confirmed cases increased from 12,107 to 54,353. By 2024, the numbers doubled again, reaching 334,226 probable and 123,148 confirmed cases, the highest annual number ever recorded. Overall, probable and confirmed cases increased almost fivefold over these five years, from 92,363 in 2020 to 457,374 in 2024. While these trends coincided with expanded diagnostic efforts and a higher volume of negative test results, positivity rates rose from 38.4% in 2022 to a peak of 56.9% in 2024, suggesting ongoing high levels of dengue virus circulation despite broader testing coverage.

FIGURE 1.

National dengue case trends in Mexico from 2020 to 2024. (A) Annual counts of probable (P), confirmed (C), and negative (N) cases. (B) Monthly distribution of cases over the same period, showing temporal fluctuations and seasonal peaks.

Given that the national surveillance framework does not test all suspected cases, laboratory‐confirmed counts represented only a fraction of the estimated annual burden. Based on the surveillance‐based estimation approach, confirmed cases accounted for 43.9% of estimated cases in 2020, 58.2% in 2021%, and 54.7% in 2022; however, this proportion dropped to approximately 39% in 2023 and 2024 (Supporting Information S1: Table S1). These findings indicate that laboratory‐confirmed counts likely underestimated the total dengue burden, particularly during the high‐transmission years of 2023–2024.

Temporal analysis further reveals disruption in seasonal patterns (Figure 1B). Traditionally, in Mexico, dengue peaks in the latter half of the year, especially between August and November. However, a marked shift occurred in late 2023, with case numbers remaining unusually high in November and December. This trend intensified in 2024, with an earlier onset in July, a peak in October, and sustained high transmission rates through the end of the year. These unusual transmission patterns suggest a possible disruption in dengue seasonality, with prolonged or even year‐round transmission emerging.

Moreover, the clinical profile of confirmed dengue cases in Mexico has undergone notable changes during 2020–2024 (Table 1). The hospitalisation rate varied by year, ranging from 22.9% in 2020 to a peak of 43.0% in 2023, before marginally decreasing in 2024 (38.7%). In terms of the case fatality rate, it remained relatively consistent, ranging between 0.3% and 0.4% every year, but absolute deaths increased markedly, reaching 203 in 2023 and 426 in 2024.

TABLE 1.

Case characteristics of confirmed dengue cases in Mexico, 2020–2024.

Year	Total cases	Ambulatory cases (%)	Hospitalised cases (%)	Deaths (%)	SD (%)	DWWS (%)	DWoWS (%)	Female (%)	Male (%)
2020	24,341	76.8	22.9	79 (0.3)	1059 (4.4)	4121 (16.9)	19,161 (78.7)	55.2	44.8
2021	6331	64.6	35.1	20 (0.3)	272 (4.3)	1836 (29.0)	4223 (66.7)	53.5	46.5
2022	12,107	60.9	38.6	53 (0.4)	380 (3.1)	4818 (39.8)	6909 (57.1)	54.6	45.4
2023	54,353	56.6	43.0	203 (0.4)	1609 (3.0)	24,042 (44.2)	28,702 (52.8)	54.4	45.6
2024	123,148	61.0	38.7	426 (0.3)	4009 (3.3)	51,920 (42.2)	67,219 (54.6)	55.6	44.4

Changes in the clinical classification of cases further support this trend. While DWoWS remained the most frequent category in absolute terms, its proportion among confirmed cases declined from 78.7% in 2020 to 54.6% in 2024, whereas DWWS increased from 16.9% to 42.2% during the same period, and SD remained below 5% throughout (Table 1). However, these proportions must be interpreted considering the surveillance framework. DWoWS exhibited the lowest sampling fraction, ranging from 30.5% to 54.6%, whereas DWWS and SD maintained higher sampling fractions, ranging from 63.4% to 73.5% and 72.0%–81.3%, respectively (Supporting Information S1: Table S2). Relative to DWoWS, sampling intensity was 1.31–2.41 times higher for DWWS and 1.45–2.63 times higher for SD, indicating that more severe clinical categories were disproportionately represented among laboratory‐confirmed cases.

Demographic patterns also shifted during this period (Table 1). Gender distribution among confirmed cases was quite balanced, with women accounting for between 53.5% and 55.6% annually. The average age of dengue patients showed moderate year‐to‐year variation between 2020 and 2024, decreasing from 29.5 years in 2020 to a low of 26.1 years in 2023, before rising again to 29.3 years in 2024, approaching 2020 levels.

4. Geographic Dispersion of Confirmed Dengue Cases

Spatial analysis revealed that although most Mexican states reported at least some dengue activity each year, a small group consistently accounted for most confirmed cases, resulting in a highly uneven geographic distribution across the country (Figure 2). The heatmap (Figure 2a) illustrates a progressive intensification of dengue activity from 2020 to 2024, with persistent hotspots and occasional large spikes in low transmission areas. These patterns should be interpreted as the geographic distribution of laboratory‐confirmed cases under the surveillance framework, rather than as a direct representation of the total dengue burden. To further characterise this heterogeneity, states were grouped into high, moderate, and low‐transmission categories following the transmission‐risk stratification framework of Baak‐Baak C.M. et al. [10], based on their average contribution to national confirmed dengue cases during 2020–2024 (Supporting Information S1: Table S3). High‐transmission states were those above the third quartile (> 4.6%), moderate‐transmission states fell between the first and third quartiles (0.9%–4.6%), and low‐transmission states were those at or below the first quartile (≤ 0.9%).

FIGURE 2.

Confirmed dengue cases in Mexico by state and year (2020–2024). (A) Heatmap showing the number of cases per state. (B) Annual proportional maps showing the relative contribution of each state to the national total. Proportions were normalised by the total number of confirmed cases per year, with darker colours indicating a higher share of the national burden.

High‐transmission states included Chiapas (5.0%), Coahuila (6.1%), Guerrero (5.6%), Jalisco (8.7%), Morelos (5.9%), Sinaloa (7.0%), and Veracruz (12.2%). Collectively, these states accounted for 42%–75% of annual confirmed cases despite year‐to‐year fluctuations. For instance, Jalisco contributed 22.1% of national cases in 2020 and 16.5% in 2024, whereas Veracruz reported 15.4% in 2021, 13.7% in 2022%, and 19.3% in 2023. Since 2021, Chiapas, Guerrero, and Morelos have maintained annual proportions exceeding 5%.

States with moderate transmission included Michoacán (4.4%), Nuevo Leon (4.0%), Oaxaca (3.8%), Puebla (3.4%), Quintana Roo (3.1%), Sonora (4.2%), State of Mexico (3.2%), Tabasco (3.7%), and Yucatán (4.0%). Although their contributions were generally lower than those of high‐transmission states, several registered exceptional peaks, such as Sinaloa in 2021 (22.0%), Sonora in 2022 (18.2%), Yucatán in 2023 (19.6%), and Quintana Roo in 2023 (9.2%). The remaining states were classified as low‐transmission.

Beyond the historically high‐transmission states, sustained activity and atypical peaks were recorded in regions not traditionally linked to high incidence. Coahuila accounted for 16.9% of national cases in 2021, Nuevo León for 9.4% in 2020 and 8.5% in 2024, the State of Mexico for 10.6% in 2022, and Tamaulipas for 9.5% in 2020. In 2023, isolated surges in the southeastern region, particularly in Quintana Roo and Yucatán, indicated local amplification events. Regionally, the South (Quintana Roo, Tabasco, Veracruz, Yucatán) showed consistently high or rising contributions, with multiple states exceeding 10% in peak years. In the central region, Morelos and the State of Mexico displayed intermittent spikes. At the same time, in the northern states such as Coahuila, Sinaloa, and Sonora, large but sporadic surges highlighted the potential for epidemic expansion beyond traditional hotspots.

The proportional maps in Figure 2B further emphasise these irregularities and show a broader geographic spread in 2024 compared to earlier years. In some low‐incidence states, part of the observed burden may reflect imported cases or focal transmission events rather than sustained local transmission; however, this cannot be directly determined from the present surveillance dataset. Multiple factors, such as rising temperatures, altered precipitation patterns, urban growth, and increased human mobility, are likely to drive these changing spatial patterns. Such conditions can favour Aedes mosquito proliferation and may facilitate dengue transmission in areas not traditionally considered major hotspots. Such changes may also influence the dynamics of circulating serotypes, as explored in the following section.

5. National Dengue Serotype Dynamics

Changes in the most predominant circulating serotypes, in addition to regional factors, influenced the dynamics of dengue transmission in Mexico between 2020 and 2024. Laboratory serotyping is routinely performed in a subset of confirmed cases depending on epidemiological and clinical criteria (Supporting Information S1: Table S4). However, the available data offers insights into the virological trends, as the proportion of serotyped cases ranged from 40.2% to 57.3% across the study period, with a strong correlation (r = 0.99) between monthly confirmed cases and those serotyped, ensuring that temporal patterns in the available serotype data reflect overall case dynamics (Figure 3A).

FIGURE 3.

Temporal dynamics of dengue virus serotypes in Mexico, 2020–2024. (A) Monthly number of confirmed dengue cases (blue line) alongside serotype‐specific counts for DENV1 to DENV4. (B) Proportional distribution of dengue serotypes over time. (C) Annual summary of serotype proportions.

In 2020, DENV2 was the dominant serotype in Mexico, accounting for 78.3% of all typed cases, followed by DENV1 (20.9%), while DENV3 (0.8%) and DENV4 were nearly absent. This pattern continued in 2021, with DENV2 remaining the most frequent serotype (56.5%), although DENV1 increased to 37.7% and DENV3 reached 5.4%. In 2022, DENV2 remained the most frequently found serotype (57.1%), followed by DENV1 (17.8%). However, DENV3 increased markedly (Figure 3), making up 23.9% of serotyped cases, which signalled the start of a major shift in the circulation of serotypes. DENV4 continued to circulate at very low levels (1.2%).

By 2023, DENV3 had overtaken all other serotypes, accounting for 59.2% of all typed cases, displacing both DENV1 (16.8%) and DENV2 (21.8%). This shift was intensified in 2024, when DENV3 accounted for 86.3% of all serotyped cases, thereby making it nearly the exclusive circulating serotype in the country. In the meantime, DENV1 and DENV2 decreased to 8.3% and 4.1%, respectively. DENV4 showed no significant changes in these last 2 years and remained the least identified serotype throughout the 5 years. These patterns are summarised in Table 2 and Figure 3C, illustrating a serotype turnover from DENV2 to DENV3 and the concurrent decline of DENV1. This shift likely contributed to the explosive outbreaks of 2023–2024 as DENV3 circulated in a largely susceptible population. Such changes are recognized risk factors for widespread epidemics [15, 16, 17, 18] and coincided with higher hospitalisation rates.

TABLE 2.

Annual summary of dengue serotype proportions in Mexico, 2020–2024.

Year	# typed	DENV1 (%)	DENV2 (%)	DENV3 (%)	DENV4 (%)
2020	12,156	20.9	78.3	0.8	0
2021	3625	37.7	56.6	5.4	0.4
2022	6199	17.8	57.1	23.9	1.2
2023	21,833	16.8	21.8	59.2	2.1
2024	54,797	8.3	4.1	86.3	1.3

To assess serotype‐specific differences in disease severity, ORs were calculated using both a primary analysis (SD vs. non‐SD) and a restricted comparison of SD versus DWWS to reduce bias from differential sampling of DWoWS cases (Supporting Information S1: Table S5). DENV1 was consistently associated with lower odds of SD, including in 2020 (OR = 0.30, 95% CI: 0.21–0.43) and 2024 (OR = 0.52, 95% CI: 0.40–0.66). In contrast, DENV2 showed the strongest positive association with SD in the early years, particularly in the primary analysis in 2020 (OR = 3.09, 95% CI: 2.21–4.32) and 2021 (OR = 3.68, 95% CI: 2.10–6.45), but this association weakened thereafter. For DENV3, evidence of increased severity emerged later, reaching significance in the restricted analysis in 2022 (OR = 2.12, 95% CI: 1.47–3.05) and in the primary analysis in 2024 (OR = 1.64, 95% CI: 1.36–1.98). However, these associations were not consistently supported across both analytical frameworks, indicating that serotype‐severity patterns should be interpreted cautiously.

Overall, the replacement of DENV2 by DENV3 coincided with increased transmission and higher proportions of clinically complex cases. Although mechanisms such as antibody‐dependent enhancement (ADE) may partly explain these patterns, they cannot be directly inferred from surveillance data alone. However, serotype‐specific differences in clinical severity are well documented in dengue. For instance, a study in Nicaragua revealed that DENV1 and DENV3 had a similar proportion of severe infection in primary and secondary infections, whereas DENV2 and DENV4 showed more severity in secondary infections [19].

6. Regional Variation in Dengue Serotype Circulation

Although national trends indicate that DENV3 supplanted DENV2 during the 2023–2024 surge, a more nuanced, region‐specific pattern emerges when serotype dynamics are analysed at the state level. Serotype data were available for a subset of laboratory‐confirmed cases and therefore reflect the distribution of typed cases within the surveillance framework. Over the 5 years, the predominant serotypes varied substantially between states and years, likely reflecting differences in viral introductions, population immunity, and local ecological or transmission factors.

In 2020, as previously noted, DENV2 dominated nationally. It was the leading serotype in most states (Figure 4), particularly in northern states such as Coahuila (99.1%), Durango (99.2%), and Nuevo León (92.9%), as well as in western states including Jalisco (94.4%) and Nayarit (93.5%). Nevertheless, several states deviated from this pattern. DENV1 predominated in some central and southern states, such as Guanajuato, Morelos, Querétaro, and Yucatán (54%–84%), and accounted for a substantial proportion of cases in Michoacán, Oaxaca, San Luis Potosí, and the State of Mexico (30%–35%). Although DENV3 was uncommon nationally, it was detected in Chiapas (9.9%) and Veracruz (6.2%), suggesting early localised introductions. DENV4 was nearly absent that year.

FIGURE 4.

Dengue virus serotype proportions across Mexican states, 2020. Top: relative frequencies of DENV1–4 by state (stacked bars). Bottom: serotype‐specific choropleths. Proportions are normalised by each state's confirmed cases; grey indicates that a state has < 15 serotyped cases.

In 2021, as in 2020, DENV2 remained the predominant serotype nationally and was the leading serotype in most states (Figure 5), often exceeding 90% in Colima, Jalisco, Oaxaca, and Sonora. By contrast, DENV1 predominated in Guanajuato (90.9%), Morelos (61.4%), and San Luis Potosí (68.4%) and contributed substantially to Chiapas, Nuevo León, and the State of Mexico (35%–56%). Notably, DENV3 expanded relative to 2020, reaching higher levels in both northern and southern states, including Chiapas (33.3%), Nuevo León (16.7%), San Luis Potosí (5.3%), Sinaloa (6.9%), Sonora (4.8%), and Tabasco (69.0%), where it became locally dominant. DENV4 circulation remained minimal, peaking only in Chiapas (9.4%).

FIGURE 5.

Dengue virus serotype proportions across Mexican states, 2021. Top: relative frequencies of DENV1–4 by state (stacked bars). Bottom: serotype‐specific choropleths. Proportions are normalised by each state's confirmed cases; grey indicates that a state has fewer than 15 serotyped cases.

By 2022, DENV3 had expanded substantially relative to 2020–2021, shifting from localised circulation to sustained transmission across multiple regions (Figure 6). Its predominance was evident in northern states such as Baja California Sur, Coahuila, Nuevo León, and Tamaulipas (47%–79%) and in southern states including Campeche, Chiapas, Quintana Roo, Tabasco, and Yucatán (39%–89%). This pattern suggests multiple introductions and rapid spread across ecologically diverse areas.

FIGURE 6.

Dengue virus serotype proportions across Mexican states, 2022. Top: relative frequencies of DENV1–4 by state (stacked bars). Bottom: serotype‐specific choropleths. Proportions are normalised by each state's confirmed cases; grey indicates that a state has fewer than 40 serotyped cases.

Despite this expansion, DENV2 retained strongholds in much of western and central‐northern Mexico, with near‐exclusive prevalence in Baja California, Chihuahua, Colima, Jalisco, Oaxaca, Sinaloa, Sonora, and the State of Mexico (80%–100%). DENV1 persisted in specific locations, predominating in Guerrero (68.9%) and Puebla (80.9%) and contributing substantially to Chiapas, Michoacán, Morelos, Tamaulipas, and Yucatán (32%–44%). DENV4 circulation remained low nationwide, peaking in Chiapas (15.2%) and remaining below 3% elsewhere.

In 2023, DENV3 became the predominant serotype nationwide, with its highest prevalence concentrated in the southern region (Figure 7), particularly in Campeche, Quintana Roo, Tabasco, and Yucatán (89%–99%), while also reaching notable proportions in the north (Coahuila 74.6%). DENV1 remained prevalent in some northern states (Baja California Sur 82.5% and Sinaloa 62.2%), in the west (Jalisco 50.3%, Nayarit 35.4%, and Colima 42.1%), as well as in central states like Puebla (55.9%). DENV2's dominance was restricted mainly to southern states such as Michoacán (55.4%), Oaxaca (76.7%), and Veracruz (62.0%), though it retained moderate prevalence in several other regions.

FIGURE 7.

Dengue virus serotype proportions across Mexican states, 2023. Top: relative frequencies of DENV1–4 by state (stacked bars). Bottom: serotype‐specific choropleths. Proportions are normalised by each state's confirmed cases; grey indicates that a state has < 50 serotyped cases.

This year was notable for its serotype diversity. DENV1 predominated in six states (≥ 50% of cases), DENV2 in three, and DENV3 in nine, while seven states exhibited substantial co‐circulation of two or more serotypes, consistent with complex transmission dynamics and heterogeneous immunity profiles. DENV4 circulation remained minimal, peaking in Coahuila (9.5%).

By 2024, DENV3 had become the overwhelmingly dominant serotype nationwide (Figure 8), surpassing 90% prevalence in most states and effectively replacing other serotypes in much of the country. Its dominance was nearly absolute in large parts of both northern and southern Mexico, including Campeche, Colima, Jalisco, Morelos, Nayarit, Querétaro, Quintana Roo, Sonora, Tamaulipas, and Yucatán, where it accounted for over 90%–99% of typed cases.

FIGURE 8.

Dengue virus serotype proportions across Mexican states, 2024. Top: relative frequencies of DENV1–4 by state (stacked bars). Bottom: serotype‐specific choropleths. Proportions are normalised by each state's confirmed cases; grey indicates that a state has fewer than 40 serotyped cases.

Nonetheless, pockets of resistance to complete serotype replacement persisted. DENV1 remained predominant in Aguascalientes (65.9%) and Chihuahua (91.7%) and was still present at moderate proportions in Hidalgo (35.7%). DENV2, though nearly absent at the national level, retained moderate circulation in Michoacán (21.1%), State of Mexico (15.2%), and Puebla (10.0%) and was detected at low levels (< 8%) in several other states. DENV4 circulation remained negligible, with proportions not exceeding 8% anywhere in the country. This near‐complete serotype homogenisation marks the culmination of the DENV3 expansion that began in 2022, leaving only a few regional enclaves where other serotypes continue to persist.

7. Environmental and Ecological Considerations

The ecological analysis focused on DENV3 because consistent circulation and sufficient case counts were observed from 2022 onward in the surveillance data. In earlier years (2020–2021), DENV3 was absent or sporadic in multiple states, yielding sparse or zero counts that undermine state–year modelling (unstable estimates, separation issues) and reduce statistical power. Given the surveillance‐based nature of serotype data, these ecological associations should be interpreted with caution.

At the state–year level (after applying the ≥ 40‐case threshold), higher annual mean temperature was consistently associated with higher DENV3 proportions across states (per +1°C: 2022 OR 1.60 [95% CI 1.54–1.66]; 2023 OR 1.57 [1.55–1.59]; 2024 OR 1.34 [1.33–1.36]; all p < 0.001). These results suggest that temperature may play a role in shaping the spatial distribution of DENV3 across Mexico. The precipitation association varied between states and years: no significant state‐level association in 2022 (OR 1.07 [0.91–1.26], p = 0.397), a negative state‐level association in 2023 (drier states with more DENV3; OR 0.51 [0.47–0.56], p < 0.001), and a positive state‐level association in 2024 (more humid states with more DENV3; OR 1.24 [1.20–1.29], p < 0.001). This variability highlights substantial inter‐annual and regional heterogeneity in precipitation effects, suggesting that its influence may depend on local ecological conditions.

A pooled state–year analysis with year fixed effects supported a robust temperature effect (OR 1.44 [1.43–1.45], p < 0.001) and a modest positive overall precipitation effect (OR 1.10 [1.06–1.14], p < 0.001), consistent with the observed variability across individual states.

8. Conclusion and Discussion

This study highlights dengue's fast and ongoing spread in Mexico, where the annual disease distribution has shifted from seasonal outbreaks to a more prolonged high‐burden transmission. From 2020 to 2024, the country experienced an unprecedented increase in dengue cases, with confirmed cases peaking in 2024, with more than 123,000 confirmed cases. Although dengue has been considered endemic in southern and coastal states, in recent years, several outbreaks have been reported in northern and central regions, indicating a concerning geographic expansion. Moreover, detecting unusual transmission increases in winter suggests a disruption in traditional seasonal patterns.

These changes in the distribution and circulation are not unique to Mexico and have been reported elsewhere [3, 9, 16, 18]. Several factors may be contributing to the intensification of dengue circulation, including sociodemographic factors and vector range expansion due to climate change. In particular, rising temperatures and changing precipitation patterns may contribute to extending the breeding season and vector competence [20, 21, 22], while frequent human movement likely facilitates viral dissemination between regions [23]. Notably, a recent introduction into America of a DENV3 clade was detected in Brazil and later expanded through the continent and may have contributed to the increasing frequency of this serotype in Mexico [15, 24, 25, 26, 27]. Under these circumstances, viral clade replacement and changes in population‐level immunity, especially after a new dominant serotype emerges, may increase the risk of severe dengue through mechanisms such as ADE.

A marked serotype shift occurred during this period: DENV2 dominated in 2020, shared predominance with DENV1 in 2021, and was progressively displaced by DENV3 from 2022, culminating in near‐complete dominance in 2024. Historically, DENV1 and DENV2 have alternated in dominance in Mexico since 2007 [28], making the rapid rise of DENV3 an unusual and significant event. However, this replacement was not uniform across the country. DENV3 emerged early in key northern and southern states, whereas DENV1 persisted in parts of the central and northern regions. Some states retained DENV1 or DENV2 dominance well after the national shift, and DENV4 circulation, although consistently low, persisted in certain areas. These patterns reveal regionally specific dynamics shaped by viral introductions, local immunity profiles, and ecological conditions.

An important methodological consideration is that Mexico's dengue surveillance system differentially samples cases according to clinical severity. Because dengue without warning signs is tested less intensively than dengue with warning signs and severe dengue once local transmission is established, laboratory‐confirmed cases represent a surveillance‐derived subset rather than a fully population‐representative sample. As a result, confirmed cases likely underestimate the true burden of non‐severe dengue, particularly during high‐transmission years. Similarly, serotype distributions reflect only typed confirmed cases and may not fully capture the complete distribution of circulating serotypes.

This surveillance framework also has implications for the interpretation of serotype‐specific severity analyses. Because severe cases are more completely represented than non‐severe cases, associations between serotype and severe outcomes may be inflated in the primary comparison of SD versus all non‐SD cases. For this reason, the restricted comparison of SD versus DWWS provides a more conservative assessment of serotype‐severity patterns. Under this interpretation, DENV1 showed a consistent association with lower odds of severe dengue, DENV2 showed stronger associations with severity in the early years, and DENV3 showed later signals of association that were not consistently reproduced across both analytical frameworks. Therefore, these findings should be interpreted as differences in severity patterns within the surveillance dataset rather than as direct population‐level estimates of serotype‐specific risk.

Climatic analysis showed that higher mean temperatures were consistently associated with increased DENV3 prevalence, while precipitation effects varied markedly between years. This suggests that temperature may be a more stable large‐scale correlate of DENV3 expansion, while the role of precipitation is likely shaped by local ecological and environmental conditions. Together, these findings support the idea that the recent dengue dynamics in Mexico reflect the interaction of virological change, climatic suitability, and heterogeneous regional transmission contexts.

From a public health perspective, understanding these spatial, temporal, and serotype‐specific dynamics is essential for anticipating outbreak intensity, strengthening surveillance, improving laboratory capacity, and guiding prevention strategies. As dengue continues to expand its range in Mexico, coordinated, region‐specific, and evidence‐based interventions will be critical to improve case detection, clinical preparedness, and timely public health response.

Author Contributions

Blanca Taboada: conceptualisation, format analysis, software, project administration, manuscript writing, and editing. Selene Zárate: conceptualisation, project administration, and manuscript writing. Lorena Díaz‐González: data curation, software and review and edit the manuscript. Juan Manuel Hurtado: data curation, visualisation and review and edit the manuscript. All authors approved the final version for submission.

Funding

This project was partially supported by grants CONAHCyT (302979 to S.Z.), SECIHTI (CBF‐2025‐I‐1026 to B.T.), UACM CCYT‐2023‐IMP‐08 (S.Z.), and UNAM DGAPA‐PAPIIT (IN225126 to B.T.).

Ethics Statement

The authors have nothing to report.

Consent

The authors have nothing to report.

Conflicts of Interest

The authors declare no conflicts of interest.

Permission to Reproduce Material From Other Sources

The authors have nothing to report.

Supporting information

Supporting Information S1

Data Availability Statement

Data sharing not applicable to this article as no datasets were generated or analysed during the current study.