At present, COVID-19 was wreaking havoc on the world and has brought enormous burden to the people's economy and health. To curb the rapid spread of COVID-19, different levels of non-pharmaceutical interventions (NPIs) have been implemented. These measures have effectively suppressed COVID-19's rapid propagation. However, it has affected the prevalence of other infectious diseases to varying degrees. Among them, dengue fever, as the fastest spreading recurrent arbovirus disease, has had a great impact on people all over the world (15). At present, the reports on the impact of COVID-19 are various in different countries. Therefore, in this study, we intended to explore the possible influence factors on dengue epidemic by analyzing the characteristics of dengue epidemic in different countries under COVID-19.
The results of correlation analysis on the potential relevant factors showed that the dengue cases subtractions were significantly negatively related to the territory area, the total number of COVID-19 cases and the number of COVID-19 deaths. In many countries, the implementation of various NPIs and the medical health care could not be fully collected and precisely measured. Therefore, we used the total number of COVID-19 cases to indicate the implementation of NPIs, that is, to a certain extent, the higher the cases, the worse the implementation of prevention and control (32–36). Also, the medical treatment of the current year was indicated by the total deaths, mortality and fatality of COVID-19, that was, the higher the occupation of medical resources for the prevention and control of COVID-19, the worse the medical intervention for dengue, and the higher the total number of deaths. The correlation above indicated the impact of COVID-19 epidemic on dengue fever. Finally, the negative correlation between dengue subtractions and territory areas indicated that when facing global pandemic, countries with larger territories can exert advantage in dengue prevention. As for rank sum analysis, results showed that there were significant differences in dengue fluctuations of countries with different continental locations, 2019 and 2020 GDPs per capita, gaps between two years, territory areas, populations and coronavirus occurrences.
Differences in territories may due to the strong correlation between dengue vector distribution and the location. As the host of dengue virus, Aedes aegypti is widely distributed in South America and Southeast Asia. On the other hand, dengue is also mainly affected by local weather, and there may be different weather conditions in the same region, therefore, the number of epidemic changes measured here is consequently less affected by the climate zone. Therefore, it is still suggested that countries in those regions should be vigilant against the outbreak of dengue fever in the face of large-scale lockdown.
Furthermore, this study proved that different countries’ economies of two years were affected during the COVID-19 pandemic, which were speculated that it had an impact on dengue surveillance and treatment. In other words, implementation of dengue prevention were highly various due to the countries’ own and COVID-19-affected economy. Consequently, as a country's economy was a determined factor of whether it can effectively combat dengue, in face of large-scale infectious diseases pandemic, countries of different developed degrees should formulate economic distribution measures in line with national conditions to deal with the economic recession in the pandemic.
While population size of a country can affect the fluctuation of dengue, we believed that as the average density was obtained by the ratio of population to territorial area, it has not been investigated at the urban level. The impacts on dengue fluctuation induced by the uneven demographic distribution can strongly surpassed the average model. Therefore, the population density in this analysis would be different from reality in dengue epidemic areas, so more data were needed to fully explain this conclusion.
Among many measures, lockdowns and border restrictions were considered capable of inhibiting the imported cases overseas and the spreading of dengue. In the case of COVID-19's outbreak and dissemination, many countries have adopted NPIs, such as Spain, China, Malaysia and other places (6, 7, 31). Furthermore, international tourists were often regarded as the cause of cross-border transmission of dengue (38–40), so the restrictions could slow down the dengue fever propagation from high incidence areas to other regions (41, 42). Studies have shown that COVID-19's travel restrictions had a positive effect on dengue fever epidemics in many European countries (42). Also during COVID-19 pandemic, it was the isolation of the close contacts, the monitoring methods and the epidemic information release on large datasets that effectively suppressed coronavirus pandemic. Furthermore, strict NPIs have also greatly reduced the dengue epidemic in China. However, travel restrictions had little effect on areas with high incidence of dengue fever. In addition, closing crowd-gathering places such as schools and lockdowns centered on families and communities were also important restrictive measures for the prevention and control of COVID-19 (5). This reduction in mobility between families can inhibit the spread of dengue fever. Reports showed that the daily activities of infected individuals and their contacts were often similar. Therefore, daily human activities played a key role in the spread of vector borne pathogens. Consequently, when the lockdown was limited to small families, the possibility of transmission from one household to another was reduced (43). All these help to explain the reduction of dengue epidemic in most countries under COVID-19.
It is acceptable that the impact of NPIs against COVID-19 on dengue epidemic existed globally, but this impact was not absolute. No matter how worse the COVID-19 pandemic, countries should pay attention to the prevention and control of dengue, especially in low-income countries where dengue fever is prevalent. Considering that COVID-19 and dengue might share the similar clinical manifestations that affect the medical control and diagnosis (31, 44–46) and the overlap outbreak will lead to competition for medical resources (47–50), countries should formulate strategies for their own situation and strictly control the dengue epidemic. The data collection of this study is limited. With the inclusion of more types of data in the future, the impact of COVID-19 on the dengue epidemic will be more comprehensively displayed. This can also provide data support and theoretical basis for timely adjustment of dengue epidemic prediction, prevention and control when dealing with the impact of major new and recurrent infectious diseases in the future.