Dengue vaccine: a hidden risk to Aedes aegypti control in Brazil

The approval and implementation of dengue vaccines in Brazil represent a major advance in the fight against this severe disease, which has imposed a substantial public health burden for decades. The dengue vaccines currently approved in Brazil are Dengvaxia (Sanofi Pasteur) and QDenga (Takeda Pharmaceutical), both of which use recombinant DNA technology [1], while the Butantan-DV vaccine remains under clinical evaluation. Brazil is the first country in the world to offer dengue vaccination through its public health system. The national immunization program began in February 2024 and has already reached 1,921 municipalities [2]. However, despite this important achievement and the expansion of vaccination coverage, a critical epidemiological question arises: could the introduction of the vaccine induce risk compensation behaviors, thereby reducing community vigilance and adherence to Aedes aegypti vector control measures (Table 1) [3–8].

Table 1.

Comparison of dengue vaccines currently available and those under development in Brazil

Vaccine	Indication (y)	Overall efficacy (%)	Highlights and challenges	Reference
Dengvaxia	9–45 (HIV-positive)	44–65	Risk in HIV-negative individuals, restricted use.	[3–5]
QDenga (TAK-003)	4–60	62–84	Widespread use, strong protection against hospitalization.	[6–8]
Butantan-DV	2–59 (in testing)	79.6	Single dose, promising results.	[7,8]

HIV, human immunodeficiency virus.

Although A. aegypti has a long history in Brazil, the modern dengue challenge began with the reintroduction of the virus in the early 1980s, facilitated by the resurgence of vector populations. Since the establishment of the species in the country, Brazil has experienced numerous dengue outbreaks, with endemic cycles occurring every 3–5 years, and disease incidence has increased 30-fold over the past 50 years [9–11]. This mosquito is a vector for multiple clinically important arboviruses, including chikungunya, Zika, and yellow fever. Although yellow fever vaccination is available, widely available and effective vaccines for Zika and chikungunya remain limited; consequently, vector control remains essential.

Unlike these diseases, dengue now has available vaccines; however, the perceived protection conferred by vaccination may reduce vigilance and weaken efforts by both the public and health authorities to control A. aegypti. Boccia et al. [12] hypothesized this possibility in 2013, before vaccines became available, suggesting that the population might relax vector control practices following vaccine introduction. Hadisoemarto and Castro [13] reached a similar conclusion in a study conducted in Indonesia. The concern extends beyond dengue itself to its vector. If public authorities reduce efforts to eliminate breeding sites and scale back public awareness campaigns, mosquito populations could increase, thereby elevating the incidence of diseases such as chikungunya and Zika, which continue to cause serious neurological and congenital complications and for which vaccines are still unavailable.

Although a vaccine against Zika virus infection is not yet available, several prophylactic vaccine candidates are under development [14]. Current clinical trials include the VRC5283 vaccine in Phase II studies [15–17] and ChAdOx1-based candidates [14,18]. For chikungunya, the IXCHIQ vaccine, produced by the Butantan Institute (Brazil) in partnership with the pharmaceutical company Valneva using recombinant attenuated strains, is currently undergoing Phase III clinical trials. Notably, 100% of previously infected individuals developed neutralizing antibodies after a single dose [19]. These findings reinforce the importance of maintaining efforts to eliminate mosquito breeding sites. This concern also has a historical basis. One need only recall the Rockefeller Foundation’s campaign to eradicate yellow fever, exemplified by the creation of the National Yellow Fever Service under Decree-Law No. 1,975 of January 23, 1940 [20].

Following the success of vector elimination campaigns, the Pan American Health Organization formally declared the disease eradicated in 1958 [21], and Brazil was considered free of A. aegypti. Subsequently, vector control measures ceased to be a public health priority and were progressively relaxed. However, A. aegypti persisted in the environment and, years later, facilitated the reintroduction of dengue fever into the country during the 1980s. This re-emergence may have resulted from reinfestation originating in regions where the mosquito had not been eliminated, such as Venezuela, the United States, and several Caribbean islands [22], from the resurgence of remnant mosquito populations, or from a combination of these factors. In 2013 and 2014, Zika and chikungunya viruses crossed the country’s borders and became transmissible through the same vector responsible for dengue and yellow fever transmission [23].

The coronavirus disease 2019 (COVID-19) pandemic highlighted the relationship between vaccination and behavioral change. Specifically, it illustrated the phenomenon of risk compensation, in which individuals adjust their behavior in response to perceived reductions in risk. Early in the pandemic, individuals who perceived the novel coronavirus as a significant threat were more likely to wear masks, practice hand hygiene, and avoid large gatherings as case numbers increased. However, the effects of risk compensation tend to diminish over time as the perceived novelty and threat of the disease decline [24–26].

Transmission dynamics provide another example of trade-offs associated with perceived risk. COVID-19 spreads primarily through the air, with rapid propagation in enclosed environments and strong dependence on immediate behavioral interventions. In contrast, Zika, dengue, and chikungunya require sustained environmental management to eliminate breeding sites and reduce mosquito populations over time.

A specific manifestation of risk compensation is the Peltzman effect. This effect describes a compensatory behavioral response to safety interventions, whereby reductions in perceived risk may encourage individuals to adopt riskier behaviors, potentially attenuating or even reversing some of the expected benefits of the intervention [27]. In the context of dengue fever, this mechanism could occur if expanded vaccination coverage—which reduces the individual risk of severe disease in many circumstances—leads to reduced adherence to vector prevention practices, such as decreased surveillance, less frequent elimination of household breeding sites, reduced use of protective screens, or diminished participation in community campaigns. Such behavioral changes could contribute to the maintenance or expansion of A. aegypti populations and thereby reduce the overall population-level impact of vaccination compared with predictions based solely on biological efficacy.

Two critical considerations emerge. First, the scientific literature regarding risk compensation following vaccination remains heterogeneous. El-Gilany and Abou-elwafa [28] did not identify a consensus regarding the presence of the Peltzman effect during the pandemic, whereas Henk et al. [26] suggested that the effect may occur but is attenuated when individuals perceive greater risk to others, indicating that collectivist values may mitigate the phenomenon. To address this issue, public health authorities could implement communication strategies emphasizing collective responsibility for eliminating breeding sites by engaging neighbors, schools, and community leaders to counteract individual complacency and sustain community participation. Second, dengue presents an additional biological consideration: heterogeneity in risk according to prior serological status and the potential for increased disease severity in seronegative individuals receiving certain vaccines, a distinct immunologically mediated phenomenon related to antibody-dependent enhancement (ADE) [29,30]. This relationship should be explicitly acknowledged because reduced vector control resulting from behavioral changes after vaccination may increase mosquito exposure. When increased exposure is combined with the immunological risk associated with ADE in specific subgroups, public health outcomes may paradoxically worsen, reinforcing the need to maintain rigorous environmental control measures even after vaccine implementation.

In summary, dengue vaccination may foster a sense of security that could contribute to the relaxation of other preventive measures. Individuals who believe they are protected may neglect actions such as eliminating breeding sites, thereby allowing A. aegypti populations to proliferate and increasing the risk of chikungunya and Zika outbreaks. As observed during the COVID-19 pandemic, public health communication should emphasize that vaccination must complement, rather than replace, ongoing vector control measures. Health policies should ensure sustained funding for vector control programs regardless of vaccination coverage targets so that environmental interventions are not weakened after vaccine introduction. It is therefore essential to recognize that dengue vaccination is a valuable tool, but not a standalone solution. Effective arbovirus control requires coordinated strategies, including continuous vaccination campaigns involving media outlets, schools, community health workers, and young people to encourage immunization; implementation of community incentive programs to eliminate potential breeding sites; use of real-time data to identify high-risk areas and guide interventions; maintenance or expansion of vector control resources after vaccine introduction; and continued investment in studies evaluating population behavior following vaccination.

Brazil has become a global leader in incorporating dengue vaccines into public health practice and has achieved substantial progress; however, several challenges remain, including variable vaccine uptake, differences in efficacy among vaccines and serotypes, and inconsistent public adherence to measures for eliminating natural and artificial breeding sites. Available and investigational vaccines, such as Dengvaxia, QDenga, and Butantan-DV, expand the prospects for disease control but require integrated strategies that combine surveillance, public education, and vector control to achieve sustainable impact. Public health authorities must prioritize these integrated measures because, even in the presence of effective vaccines, environmental management remains the primary defense against A. aegypti.

HIGHLIGHTS

• Dengue vaccines represent a major health advance in Brazil but may induce risk compensation behaviors.

• Perceived protection following immunization could critically reduce community adherence to Aedes aegypti vector control measures.

• Relaxed environmental management might expand mosquito populations, paradoxically increasing Zika and chikungunya transmission risks.

• Public health policies must ensure sustained funding and rigorous environmental interventions alongside ongoing vaccination campaigns.

Graphical abstract