FluSurvey works by recruiting members of the public who agree to complete weekly symptom surveys throughout the respiratory illness season. Rather than waiting for people to seek care, the system asks them directly whether they have experienced fever, cough, and other symptoms consistent with influenza-like illness, or ILI. This approach, sometimes called participatory or crowd-sourced surveillance, has gained prominence since the COVID-19 pandemic demonstrated how quickly digital reporting tools can complement traditional clinical data streams. The new study set out to characterise the wider impact of ILI among participants and to assess how closely their reports correlate with established influenza surveillance systems, including GP consultation rates, hospital admissions, and laboratory-confirmed PCR test positivity.

The analysis included data from 3,057 participants across the two winter seasons. In 2023-24, 2,540 people took part, roughly 63 percent of them female, with a mean age of 60 years. The following season drew 2,273 participants, 64 percent female, with a mean age of 61. The researchers identified 1,868 ILI episodes over the two winters and examined what happened during each one: whether the person sought healthcare, took medication, missed work or school, used a test, or found their daily activities curtailed.

The headline finding is striking in its consistency: only 14 percent of ILI episodes resulted in contact with healthcare services, most frequently a visit to the GP. In other words, roughly six out of seven episodes of flu-like illness were managed entirely outside the formal healthcare system. This has important implications for how surveillance data are interpreted. Traditional systems that rely on GP consultations see only the tip of the iceberg—the small fraction of illness severe enough, or concerning enough, to prompt a clinical visit. FluSurvey, by contrast, captures the full spectrum of community illness, including the mild and moderate cases that never appear in clinical records.

Yet the fact that most episodes avoided the doctor’s office does not mean they were trivial. A large proportion of episodes—89 percent—involved medication use, suggesting that people were actively treating their symptoms with over-the-counter remedies or prescription drugs. Three-quarters of episodes, 75 percent, were reported to have an impact on daily life, and nearly half, 47 percent, resulted in missed school or work. Absenteeism on this scale carries substantial economic and social costs, from lost productivity to disrupted childcare, that are largely invisible to health systems focused on clinical encounters.

One notable shift between the two seasons concerned testing. The frequency with which participants used tests for respiratory illness declined notably in 2024-25 compared with 2023-24. This pattern likely reflects changing habits as the acute phase of the COVID-19 pandemic recedes further into the past, with fewer people reaching for lateral flow tests or seeking PCR confirmation when they fall ill. The decline complicates efforts to track infection rates through testing data alone and underscores the value of symptom-based surveillance that does not depend on test availability or willingness to test.

The second major aim of the study was to determine whether FluSurvey’s volunteer-reported ILI rates move in step with the official signals that inform public health action. The researchers applied established methodologies, including omitting each participant’s first report—a step designed to reduce bias from people joining the survey precisely because they are ill—and weighting the data to match the age and sex structure of England. They then computed cross-correlations between weekly FluSurvey ILI rates and three national surveillance indicators: GP ILI consultations, influenza hospital admissions, and influenza PCR test positivity, at time lags ranging from two weeks ahead to two weeks behind.

The correlations were strong across the board, and their timing tells a coherent story about the natural history of an influenza season. FluSurvey ILI rates predominantly led GP ILI consultations, with a maximum correlation coefficient of 0.73. This makes intuitive sense: people experience symptoms at home before some of them eventually decide to see a doctor, so community symptom reporting provides an early warning signal of rising clinical activity. FluSurvey rates coincided most closely with influenza hospital admissions, reaching a maximum correlation of 0.88, suggesting that peak community illness aligns tightly with the period of greatest pressure on hospitals. Meanwhile, FluSurvey ILI lagged behind influenza PCR test positivity, with a maximum correlation of 0.88, which fits the expectation that laboratory-confirmed cases among tested patients rise before broader community symptoms peak—or that testing is concentrated early in illness episodes among those who choose to test.

For public health officials, these timing relationships matter. A surveillance signal that leads GP consultations by even a week or two can buy valuable time for interventions such as vaccination campaigns, antiviral distribution, and hospital surge planning. The strong correlation with hospital admissions indicates that FluSurvey is not merely detecting trivial sniffles; the aggregate pattern of community-reported symptoms tracks the severe end of the epidemic curve remarkably well. And the fact that the signal holds up across two distinct winter seasons, with different circulating virus profiles and participant cohorts, lends confidence that the findings are robust rather than a one-off artefact.

The study also highlights the complementary nature of participatory surveillance. It does not replace laboratory testing, which provides virological specificity, or clinical reporting, which captures healthcare burden. Instead, it adds a community-level layer that contextualises the clinical data: how much illness is out there that never reaches a clinic, how it affects work and daily life, and how people manage it on their own. As the authors conclude, the majority of ILI reported to FluSurvey does not involve contact with healthcare services, but it carries wider impacts on daily life, and FluSurvey ILI corresponds well with other national influenza surveillance while providing broader context on community illness. In an era when respiratory virus threats demand rapid, granular situational awareness, systems that enlist the public as sensors may prove an increasingly essential part of the surveillance toolkit.

Subject of Research: Participatory surveillance of influenza-like illness in the UK using FluSurvey over the 2023-24 and 2024-25 winter seasons

Article Title: Monitoring influenza-like symptoms in the UK through participatory surveillance: Insights from FluSurvey over two winter seasons (2023-24 and 2024-25)

Article References: Green, R. E., Mellor, J., Rawlinson, C., Waller, E., Abdul Aziz, N., Watson, C. H., & Dabrera, G. (2026). Monitoring influenza-like symptoms in the UK through participatory surveillance: Insights from FluSurvey over two winter seasons (2023-24 and 2024-25). PLOS Digital Health, 5(10), e0001714. https://doi.org/10.1371/journal.pdig.0001714

Image Credits: AI Generated

DOI: 10.1371/journal.pdig.0001714

Keywords: influenza, FluSurvey, participatory surveillance, influenza-like illness, UK Health Security Agency, public health, epidemiology, respiratory viruses, GP consultations, hospital admissions, PCR test positivity, winter seasons

The central message of the work is not that green spaces are dangerous, but that their effects on vector-borne disease are complex, context-dependent, and likely to shift as the climate changes. Urban greening has become a cornerstone of city planning across the world, promoted for cooling overheated neighborhoods, absorbing stormwater, reducing air pollution, and improving residents’ wellbeing. At the same time, warming temperatures are expanding the geographic range and lengthening the active seasons of several arthropod vectors, including mosquitoes and ticks, in parts of the world where they were previously limited. The Exeter and UK Health Security Agency team contends that these two trends, greening and warming, do not operate in isolation, and that policies designed around one of them should not ignore the others.

Vector-borne diseases, in which pathogens are transmitted to humans by organisms such as mosquitoes, ticks, and other biting arthropods, already account for a large share of the global infectious disease burden. Climate change influences this burden in several ways. Temperature affects the survival, development rate, and biting behavior of vectors, as well as the replication rate of pathogens inside them. Altered rainfall and humidity patterns shape the availability of the standing water that mosquito larvae need and the moisture conditions that ticks require to survive. In urban environments, these relationships are further modified by the built landscape: drainage systems, heat islands, irrigated gardens, and green corridors all create distinctive microhabitats that can either support or suppress vector populations.

Urban green spaces sit at the heart of this interaction. Vegetated areas can provide habitat for wildlife hosts that feed ticks and mosquitoes, hold moisture that favors tick survival, and collect water in tree holes, plant containers, or poorly maintained features that mosquitoes can exploit for breeding. Yet the same spaces can also support natural enemies of vectors, reduce local temperatures in ways that push conditions outside the range some vectors tolerate, and be designed and maintained so that they harbor fewer breeding sites. The researchers emphasize that the net effect of any given green space on disease risk depends on its design, its management, the local vector species present, and the climatic trajectory of the region, which is precisely why they argue for careful, evidence-based consideration rather than blanket assumptions in either direction.

The team’s argument is framed as a call for critical decision-making. They encourage planners, public health authorities, and researchers to consider potential interactions between urban green spaces, vector-borne diseases, and climate change as part of efforts to maximize public health benefits and reduce risks. In practice, this means that when a city evaluates a proposal for new parks, tree planting schemes, wetlands, or green infrastructure, the assessment should extend beyond carbon, heat, and wellbeing outcomes to include the possible consequences for vector ecology. It also means that surveillance of mosquitoes and ticks in urban areas becomes more important as warming shifts which species can establish where, so that any emerging risks can be detected and managed early.

The multidisciplinary composition of the group is itself part of the argument. Questions about how a new urban wetland might change mosquito abundance, or how street trees might alter the microclimate experienced by ticks, cannot be answered by any single discipline. They require ecologists who understand vector and host populations, climatologists who can project local conditions, epidemiologists who can model disease transmission, and public health practitioners who know how interventions are delivered on the ground. By bringing these perspectives together, the researchers aim to move the conversation beyond a simple trade-off narrative, in which green space is either an unqualified good or a hidden hazard, toward a more nuanced framework in which design and management choices determine outcomes.

This nuance matters because the stakes are high on both sides of the ledger. The health benefits of urban vegetation are among the most consistently supported findings in environmental health research, encompassing reduced heat stress during heatwaves, opportunities for physical activity, stress reduction, and improved social cohesion. With heatwaves intensifying and cities warming faster than many surrounding areas because of the urban heat island effect, greening is widely regarded as an essential adaptation strategy. Discouraging greening out of an exaggerated fear of vectors could therefore cause real harm. Conversely, ignoring the ecological consequences of greening could allow conditions favorable to vectors to develop unnoticed, particularly in regions where warming makes previously marginal environments newly suitable for species capable of transmitting pathogens to humans.

The researchers also highlight that climate change acts as an amplifier of uncertainty in this system. As average temperatures rise and extreme weather becomes more frequent, the baseline conditions against which green space effects must be judged are themselves moving. A park that poses little vector concern under today’s climate might behave differently under warmer, wetter, or more drought-prone conditions decades from now. This dynamic character of the risk landscape is a key reason the team points to the twenty-first century as the period in which these decisions will be most consequential, and why they advocate that consideration of these interactions be built into planning processes now rather than retrofitted after problems emerge.

For the United Kingdom specifically, the involvement of the UK Health Security Agency reflects growing institutional attention to the health effects of a changing climate, including the monitoring of vector species whose ranges have been shifting northward in Europe. The agency’s participation alongside academic partners underscores the article’s premise that these questions belong squarely within the remit of public health protection, not only within environmental planning or nature conservation. The work was supported by workshop funding from the Environment and Sustainability Institute at the University of Exeter as part of its Think Tank programme, with additional support acknowledged through the Centre for Net Positive Health and Climate Solutions, funded by UKRI, and through an NIHR Population Health Career Scientist Award. The authors declared no competing interests.

Ultimately, the article in PLOS Climate, titled Balancing urban green space benefits and vector-borne disease risk under climate change: Critical decision-making for 21st century public health, is best read as a roadmap for integrated thinking rather than a warning against greening. Its authors ask decision-makers to hold three realities in view simultaneously: that urban green spaces deliver major and growing public health benefits that cities urgently need in a warming world; that climate change is altering the distribution and behavior of the organisms that transmit vector-borne diseases; and that the design, placement, and management of green infrastructure can influence which of those organisms find suitable habitat in towns and cities. Treating these as separate policy silos, the researchers suggest, risks either under-protecting communities from emerging disease risks or undermining the greening agenda on which urban health so heavily depends. The path they advocate is one of informed, multidisciplinary, and adaptive decision-making, in which surveillance, ecological understanding, and public health goals are combined so that greener cities can also be safer ones.

Subject of Research: Interactions between urban green spaces, vector-borne disease risk, and climate change in public health planning

Article Title: A multidisciplinary group of researchers from the University of Exeter and the UK Health Security Agency encourage consideration of potential interactions between urban green spaces, vector-borne diseases, and climate change

Article References: A multidisciplinary group of researchers from the University of Exeter and the UK Health Security Agency encourage consideration of potential interactions between urban green spaces, vector-borne diseases, and climate change. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: urban green spaces, vector-borne diseases, climate change, public health, mosquitoes, ticks, urban planning, PLOS Climate, University of Exeter, UK Health Security Agency, disease surveillance, urban heat island