The coronavirus disease 2019 (COVID-19) pandemic, caused by the emerging severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), is now a major health crisis. By mid July 2020, there had been about 14 million cases and more than 600,000 deaths worldwide, and there have been massive economic consequences and social disruption. While this global crisis rightly demands the world’s attention, many other infectious diseases are still on the rise and risk increasing further as the focus shifts away from them. This is the case with dengue fever, a viral disease transmitted by Aedes mosquitoes, whose incidence has increased dramatically over the past decade [1], with severe epidemics currently affecting Latin America, Asia, and the Indian Ocean [2–6]. Brazil, for example, is currently experiencing the largest ever dengue epidemic, with nearly 800,000 cases and 221 deaths between January and April 2020 [3,7] (Fig 1, panel A). Similarly, Southwest Indian Ocean islands, such as La Réunion and Mayotte (two French overseas departments), are experiencing unprecedented dengue outbreaks, with more than 30,000 cases reported on the islands since 2017 [5,6] (Fig 1, panel B). At the same time, other arboviruses also transmitted by Aedes mosquitoes, such as chikungunya, Zika, and yellow fever, continue to occur in many parts of the world [10], and temperate regions of the Northern Hemisphere (United States and Europe), which are particularly affected by the COVID-19 pandemic, are also threatened by autochthonous transmission of dengue, chikungunya, and Zika in areas where the vectors A. aegypti and/or A. albopictus are established [11].

In April 2020, in a context of concurrent epidemics of dengue and COVID-19 in the French overseas departments, the French Ministry of Health tasked the French Agency for Food, Environmental and Occupational Health & Safety (ANSES) with setting up a multidisciplinary task force of experts to assess the impact of the COVID-19 pandemic and lockdown (imposed from 17 March to 11 May in France) on dengue surveillance and vector control interventions. Their report was recently published [12], and in this letter, the task force presents the results of its expert assessment and its recommendations to the global health community.

Concurrent circulation of COVID-19 and dengue can lead to a delay in diagnosis and may therefore negatively affect the management, care, and control interventions specific to each of the 2 diseases. Differential diagnosis is required because the 2 viral infections share certain clinical features, such as fever, fatigue, and headache [4,13–16]. In addition, concern has been raised over the discovery of cases of false-positive dengue serology in individuals with COVID-19 [17]. Confusion in diagnosis or in test results can have dramatic consequences not only for patients but also for public health control interventions (e.g., contact tracing in the case of COVID-19 and vector control in the case of dengue). Co-circulation of the 2 viruses in the same regions exacerbates the health risk because of the potentially critical consequences of both infections in terms of morbidity and mortality, especially in severe cases. Although co-infection of dengue and COVID-19 has so far been only sporadically documented in Thailand, Singapore, Mayotte, and La Réunion islands [16,18], it is raising serious concerns in countries affected by dengue outbreaks, particularly in Southeast Asia and South America [2–4, 13–20]. Healthcare services in many countries have already been disrupted or even overwhelmed by the COVID-19 pandemic, and co-occurrence of the 2 diseases often aggravates the situation. This is particularly worrying in regions where several dengue serotypes are co-circulating and where secondary or even tertiary infections have been recorded [5,7]. Epidemiological surveillance of dengue has also been detrimentally affected. In all the French overseas departments, there was a drop in declared notified dengue cases just after the start of the lockdown (epidemiological weeks 12–13, Fig 1, panel B), even though there had been a marked increase in the number of cases over the previous weeks [12]. Underreporting of dengue, notable for paucisymptomatic cases, can be attributed not only to lockdown and to difficulties in moving around, even for medical reasons, but also to public concern over the risk of being infected by COVID-19 in health facilities, the closure of some clinics, and disrupted access to diagnosis [12]. The COVID-19 pandemic also affects vector control of Aedes mosquitoes in drawing attention and collective mobilization away from dengue and other arboviral diseases and their vector mosquitoes. In the wake of the COVID-19 crisis and lockdown, vector control interventions were scaled down in all the French overseas departments, social mobilization campaigns were put on hold, and preventive insecticide spraying was curtailed, especially in private spaces (indoor and peridomestic spraying) [12]. In the absence of vaccines and therapeutic treatment, the prevention and control of dengue and other Aedes-borne viral diseases continues to rely heavily on controlling mosquito vector populations or on interrupting human–vector contact through integrated, sustainable, synergic, and proactive vector management [1,21]. Failure to appropriately implement the full range of vector control interventions can reduce their overall effectiveness [1,21]. In fact, many of the interventions that are an essential part of an effective dengue control programme targeting private properties—such as indoor residual spraying, door-to-door campaigning, source reduction, and peridomestic residual spraying (Table 1)—are at odds with the guidelines for COVID-19 prevention and lockdown, simply because they require or may entail close contact between the vector control teams and the resident population. As such, interventions forming the core of efficient dengue control are expected to be significantly scaled down in many areas of the world where they are commonly carried out [1,12]. In an effort to fill this gap, while acknowledging the effectiveness of social mobilization in the control and prevention of Aedes-borne diseases [1,21], we consider it is crucial to strengthen communication for social mobilization against these diseases using digital communication tools and social networks jointly with the dissemination of information concerning COVID-19 (e.g., eliminating mosquito breeding sites while staying home), and to adapt existing guidelines to meet the current situation (Table 1) [19, 20]. Thus, vector control workers should use personal protective equipment and physical distancing while carrying out any vector control interventions, including those targeting larvae and adult mosquitoes, as well as community-based control measures (Table 1) [12,19,20]. In addition, local teams that know how to make information more effective in the field [20] could combine messages aimed at strengthening household and community participation in vector control measures with COVID-19 prevention and best practice messages [19,20]. Consequently, it is essential to reaffirm the crucial role of vector control staff, not only for dengue control measures but also to leverage community ownership and engagement in public health, and in particular to ensure the safety of these agents facing COVID-19, so that they can guarantee the safety of populations confronted with dengue fever.

The negative impact of the COVID-19 crisis on dengue surveillance and control is obvious in tropical areas affected by dengue epidemics, but the risk of local cases of dengue and other arboviruses in temperate regions is expected to be lower as travel restrictions limit the opportunities for viral importation. However, the risk is still there, as 14 dengue cases were imported into European France during the lockdown period from 17 March to 11 May 2020, despite the very low number of flights returning from dengue-affected areas [12]. The resumption, even partial, of air transport this summer will bring with it a risk of viraemic travellers returning from regions affected by these arboviruses during the vector season in Europe [11,12]. Neglecting early vector control intervention around imported cases may also increase the risk of autochthonous cases of arbovirus [11]. Finally, the adverse economic and social consequences could be aggravated by concurrent circulation of these diseases. Social inequalities in relation to dengue and other arboviruses, such as Zika, have been highlighted [22]. Similarly, it has recently emerged that the COVID-19 pandemic is exacerbating social inequalities, as has been shown in the French overseas departments, such as La Réunion and Mayotte, as well as in the US [23,24].

Public health systems are faced with the challenge of co-circulation of dengue and COVID-19 and the many detrimental outcomes—which include co-infections; delays in diagnosis, treatment, and mitigation measures; overwhelming of healthcare systems; underreporting of cases; deterioration of surveillance and vector control interventions; and exacerbation of social inequalities. If the effectiveness of vector control measures is compromised, this can have serious consequences for public health. We have therefore put forward a framework for dealing with these risks on a global level (Table 1) [12]. As highlighted earlier [19,20], we have drawn attention to the importance of maintaining and strengthening integrated management of mosquito-borne diseases—especially surveillance, vector control in private spaces (door-to-door campaigns, indoor and peridomestic sprayings) and social mobilization—during the COVID-19 pandemic, and to the importance of upgrading guidance to take into account the need to minimise workers and citizens being exposed to risk. Even as several countries are unlocked, there is wide concern over the possibility of a second wave of the COVID-19 epidemic, and a new (strict or partial) lockdown is underway in some regions [25]. Throughout the world, we are facing an imminent potential risk of arboviral diseases, such as dengue fever, chikungunya, Zika, and yellow fever, surging simultaneously due to a deterioration in surveillance and vector control and giving rise to a more severe situation than the COVID-19 pandemic alone. We urge the health community and policy makers to urgently develop proactive policies and allocate adequate resources to prevent and manage the resurgence of vector-borne diseases in the new era of COVID-19. More broadly, in the context of the risk of new emerging disease occurrence with high epidemic and pandemic potential, advance preparedness will be essential to maintain and strengthen vector-borne disease control activities.