Reconstructing Dengue Exposure Dynamics and Assessing the Public Health Impact of Vaccination Scenarios Using Mathematical Models in Brazil
This study reconstructs Brazil's state- and age-specific dengue immunity profiles using 2000–2025 surveillance data to demonstrate that optimal vaccination strategies depend on local susceptibility, with prioritizing children maximizing DALY reductions and targeting the elderly minimizing mortality, particularly under constrained vaccine supply.
Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of a preprint that has not been peer-reviewed. It is not medical advice. Do not make health decisions based on this content. Read full disclaimer
Dengue fever is a mosquito-borne illness that has long plagued tropical regions, but its behavior is far from uniform across the globe. In places where the virus has circulated for decades, most people have been infected at least once, often without realizing it, building up a complex history of immunity within the population. This history matters deeply because the risk of severe disease changes depending on how many times a person has encountered the virus and their age. In Brazil, a country where dengue is endemic, the pattern of infection has shifted dramatically in recent years. While children have traditionally borne the brunt of the disease, older adults are now suffering the most severe outcomes, including a disproportionate share of deaths. This shift has created a difficult puzzle for public health officials: with vaccines becoming available but supplies remaining limited, who should receive them first? Should the focus remain on protecting children, who are most likely to get infected, or should it shift to the elderly, who are most likely to die if they do?
To answer this, researchers built a detailed digital map of Brazil's immune landscape, reconstructing the hidden history of dengue infections across every state and age group over the last quarter-century. They started by analyzing millions of reported cases from Brazil's national surveillance system, using a mathematical approach to infer how many people in each region had been infected once, twice, or more, even though many infections go unreported. This process revealed a striking divide: the northern and northeastern parts of the country, where dengue has been present for a long time, have populations with high levels of accumulated immunity. In contrast, the southern states, where the virus arrived more recently, have large numbers of people who have never been infected or have only been infected once. This group is particularly vulnerable because a second infection carries a higher risk of severe illness. By feeding this reconstructed history of immunity into a transmission model, the team could simulate how the disease would spread over the next five years if no vaccines were used, and then test how different vaccination strategies would change the outcome.
The simulations showed that the burden of disease in the absence of vaccination would be highest in the southern states, precisely because those populations have not yet built up the natural immunity seen in the north. When the researchers tested different ways to distribute a limited supply of vaccines—specifically, five million doses per year—they found that the best strategy depends entirely on what the goal is. If the objective is to prevent the most cases, hospitalizations, and overall years of healthy life lost, the most effective approach is to prioritize children between the ages of five and fourteen. This strategy works because children are the most likely to catch the virus, and protecting them reduces the overall amount of the virus circulating in the community, indirectly shielding others. In these simulations, focusing on this age group prevented more disability-adjusted life years than any other strategy, offering a fifteen percent improvement over current distribution trends.
However, the picture changes if the goal is to save the most lives. Because older adults are far more likely to die from dengue than children, directing vaccines toward people aged sixty and above resulted in a dramatic reduction in fatalities. In the simulations, a strategy focused on the elderly prevented more than twice as many deaths as the child-focused approach, even though it prevented fewer total cases and less overall illness. This creates a difficult trade-off for policymakers: a child-centered strategy minimizes the total suffering of the population, while an elderly-centered strategy saves the most lives but leaves more people sick. The researchers also explored what would happen if vaccine supplies were not limited. They simulated scenarios where Brazil could vaccinate up to thirty million people a year, a capacity that might become possible with new domestic production. In these high-supply scenarios, the specific choice of who to vaccinate mattered less, because the sheer volume of doses allowed for broad coverage that drastically reduced cases, hospitalizations, and deaths across the board.
The study also highlighted the importance of geography. The optimal mix of targeting children versus the elderly varied by region. In the southern states, where historical exposure has been low and the elderly population remains largely susceptible, prioritizing older adults yielded the greatest benefit in terms of lives saved. In the north and northeast, where immunity is already high, the focus on children remained more effective for reducing the overall disease burden. The researchers noted that these findings are based on simulations that rely on current data and assumptions about how the virus spreads and how well vaccines work. They did not account for potential changes in vaccine supply due to regulatory decisions or shifts in the virus itself. Nevertheless, the work provides a clear, data-driven framework for understanding that there is no single "best" way to vaccinate. Instead, the right choice depends on whether a country prioritizes minimizing total illness or maximizing the number of lives saved, and on the specific immune history of the regions it aims to protect. As Brazil navigates the rollout of new vaccines, these insights offer a way to tailor strategies to the unique realities of each state, ensuring that limited resources are used where they will do the most good.
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