Health Officials Warn of Surge in Tick-Borne Illnesses as Outdoor Season Begins

On April 23, 2026, the CDC issued an unusual mid-spring alert: weekly emergency department visits for tick bites had exceeded normal rates across most U.S. regions, reaching their highest levels since tracking began in 2017 [1]. The agency estimated that 31 million Americans are bitten by ticks each year, and roughly 476,000 are diagnosed and treated for Lyme disease alone [1]. Behind those round numbers lies a more complicated story — one involving shifting ecosystems, contested science, diagnostic gaps, and a disease burden that costs the U.S. health care system more than $1 billion annually.

The Scale of the Surge

Reported Lyme disease cases have risen sharply over the past decade, from roughly 36,000 cases per year during 2013–2016 to over 89,000 in 2023 [2]. But that headline number requires a significant caveat: in 2022, the CDC changed its surveillance methodology, allowing 15 high-incidence states to report cases based on a positive blood test alone, rather than requiring both a lab result and clinical documentation [3]. That single change drove reported cases from about 35,000 in 2021 to 62,551 in 2022 — a 1.7x increase over the 2017–2019 annual average of 37,118 [3].

Source: CDC Surveillance Data

Data as of Jan 1, 2024CSV

So how much of the surge is real? The CDC's own estimate of 476,000 annual treatments suggests that actual Lyme cases have long exceeded reported totals by a factor of 8 to 12 [4]. The reporting change narrowed that gap but did not create a new epidemic overnight. Still, disease ecologists and entomologists broadly agree that tick populations and their geographic range are expanding — a trend supported by surveillance data showing tick species like Ixodes scapularis (the blacklegged tick) establishing in counties where they were absent two decades ago [5].

Lyme disease dominates the tick-borne disease landscape, but other pathogens are gaining ground. In 2022, the CDC recorded 5,655 anaplasmosis cases, 2,867 babesiosis cases, 2,406 ehrlichiosis cases, and 2,234 cases of spotted fever rickettsiosis [6]. Babesiosis rates increased by approximately 9% per year from 2015 to 2022, with several northeastern states posting dramatic increases — Vermont saw a 1,602% rise from 2011 to 2019 [7]. More than one-third of tested ticks now carry at least one human pathogen, and co-infections are common: among babesiosis patients, 41% were also infected with Borrelia burgdorferi, the Lyme-causing bacterium [8].

Source: CDC Tickborne Disease Surveillance

Data as of Jan 1, 2023CSV

Source: CDC MMWR

Data as of Jan 1, 2023CSV

Why Ticks Are Spreading: Climate, Land, and Deer

The expansion of tick habitat is driven by multiple, interacting factors — and the scientific literature cautions against attributing it to any single cause.

Climate change is the most discussed driver. A 2025 review in PLOS Computational Biology found that warmer temperatures accelerate tick growth and development, extend seasonal activity windows, and improve overwinter survival [9]. Analysis of 20 years of surveillance data showed ticks spread faster during the warmest years, with a documented northward expansion of Ixodes ricinus reaching 66°N latitude in Scandinavia [10]. Projections under future climate scenarios consistently indicate poleward expansion of tick habitat suitability in the Northern Hemisphere [9].

But researchers stress that climate is not the only variable. A 2024 assessment in ScienceDirect found that the relative importance of climate versus landscape change and host availability "is complicated by simultaneous changes including climate warming, reforestation, and spread and population increase of white-tailed deer" [11]. Habitat fragmentation, loss of biodiversity (which reduces the "dilution effect" where diverse host species absorb tick bites that would otherwise land on pathogen reservoirs like white-footed mice), and changes in land use all affect tick-human contact [9]. Some researchers argue that improved surveillance alone explains a portion of the apparent increase — as awareness grows, more cases get tested and reported [3].

The honest assessment: multiple peer-reviewed studies support a real expansion in tick range and abundance, with warming temperatures as a contributing factor, but disentangling climate's independent contribution from land-use change, host population dynamics, and surveillance improvements remains an active area of research [9][11].

The Economic Toll

The financial burden of tick-borne disease is substantial. A study published in Emerging Infectious Diseases estimated that the economic burden of Lyme disease alone ranges from $345 million to $968 million per year in 2016 dollars [12]. A separate Johns Hopkins analysis pegged the cost at $712 million to $1.3 billion annually, or nearly $3,000 per patient on average, accounting for return doctor visits and additional testing [13].

Those figures capture direct medical costs but understate the full picture. An estimated 10 to 20% of treated Lyme patients develop persistent symptoms — fatigue, cognitive difficulties, musculoskeletal pain — that can last months or years, a condition the CDC terms "post-treatment Lyme disease syndrome" (PTLDS) [14]. The HHS Tick-Borne Disease Working Group's 2018 report to Congress noted that 30,000 to 60,000 new PTLDS cases may occur each year, contributing to lost workdays and, in some cases, long-term disability claims [14]. Per-patient costs roughly double for patients diagnosed at later disease stages compared to those caught early, at approximately $1,200 per early-stage infection [12].

For a disease that disproportionately affects rural and exurban populations — many without easy access to infectious disease specialists — these costs often fall on households with fewer resources to absorb them.

Who Gets Bitten: Demographics and Disparities

Tick-borne diseases do not affect all populations equally. OSHA identifies outdoor workers — particularly in forestry, agriculture, landscaping, and military service — as facing elevated risk [15]. Studies have found that about 20% of outdoor workers tested positive for Borrelia burgdorferi antibodies, and forestry and agricultural workers were more than twice as likely to test positive for Lyme compared to other exposed occupations [16].

Children and adolescents are another high-risk group because of outdoor play patterns, with the CDC's case data consistently showing peaks in the 5–14 age range [6]. Elderly and immunocompromised individuals face higher risks of severe outcomes, particularly from babesiosis, which can be fatal in older patients or those without a functioning spleen [7].

Racial and ethnic disparities complicate the picture. Lyme disease incidence is 1.2 to 3.5 times higher in White persons than in Asian or Pacific Islander individuals, and 4.5 to 6.3 times higher in White persons than in Black individuals [17]. This likely reflects a combination of geographic distribution (Lyme is concentrated in predominantly White rural and suburban areas of the Northeast and Upper Midwest), differences in outdoor exposure patterns, and potentially lower diagnostic suspicion in non-White patients. Hispanic individuals were less likely to conduct daily tick checks or report familiarity with Lyme symptoms [17]. In states outside traditional endemic zones, clinicians may not think to test for tick-borne diseases, leading to delayed or missed diagnoses — a problem that compounds for patients without insurance or specialist access [16].

A Diagnostic System Under Strain

The standard diagnostic protocol for Lyme disease in the United States is a two-tier approach: an initial ELISA (enzyme-linked immunosorbent assay) screening test, followed by a confirmatory Western blot if the ELISA is positive [18]. The system has well-documented limitations.

During early-stage Lyme disease — the first two to four weeks after a tick bite, when treatment is most effective — ELISA sensitivity ranges from just 35% to 50%, because the body has not yet produced enough antibodies to trigger a positive result [18][19]. Even in later disease stages, sensitivity for neurologic Lyme disease ranges from 75% to 89% [19]. The Western blot, considered the most reliable test available, is estimated to be only about 80% accurate even at the best laboratories [18]. Roughly 10% of patients with a positive IgG Western blot will have a negative ELISA, meaning the screening test misses them entirely [18].

The result is a system that works reasonably well for patients who present with the classic bull's-eye rash (erythema migrans) — which the CDC considers diagnostic on its own — but performs less reliably for patients with non-specific symptoms like fatigue, joint pain, and cognitive fog. NIAID has identified improved diagnostics as a research priority, funding efforts toward direct detection of the pathogen rather than reliance on the antibody response [20]. European countries use somewhat different testing protocols, including a modified two-tier approach using two ELISAs rather than ELISA plus Western blot, which some studies suggest offers comparable or improved sensitivity [19].

Do Prevention Campaigns Work?

Every spring, public health agencies issue the same advice: wear long sleeves, use DEET or permethrin, check for ticks after being outdoors. The question is whether anyone listens — and whether it matters.

The evidence on behavior change is mixed. Studies show that knowledge of ticks and tick-borne disease increases the likelihood of adopting protective behaviors [21]. But translating knowledge into consistent action has proven difficult. A 2021 review in the Journal of Medical Entomology identified "lack of local tick management programs staffed with public health professionals" as a major barrier, noting that the concept of area-wide integrated tick management "is groundbreaking in the United States and new models for this approach need to be developed" [22].

More concerning, the interventions that might work at scale have not performed well in rigorous trials. A large randomized controlled trial involving more than 2,700 households found that residential acaricide barrier sprays — the most common professional tick treatment — "do not significantly reduce the household risk of tick exposure or incidence of tick-borne disease" [23]. While a single springtime acaricide application kills 68% to 100% of ticks in controlled settings, this laboratory effectiveness does not translate to reduced human disease in real-world conditions [23]. Similarly, rodent-targeted bait boxes designed to treat the mice that serve as Lyme disease reservoirs did not significantly reduce household tick exposure in a Connecticut trial [24].

No U.S. jurisdiction has demonstrated a sustained, measurable reduction in tick-borne disease incidence through any single public health intervention. The most promising approaches appear to involve integrated strategies — combining habitat modification, host management, and personal protection — but these require local infrastructure that most communities lack [22].

The Vaccine Question

The most concrete development in tick-borne disease prevention is the Lyme vaccine candidate LB6V (formerly VLA15), developed by Valneva and licensed to Pfizer. In March 2026, Phase 3 trial results from the VALOR study showed 73.2% efficacy in preventing confirmed Lyme disease in individuals aged five and older, with no identified safety concerns [25]. Pfizer plans to submit a Biologics License Application to the FDA and a Marketing Authorization Application to the EMA in 2026, with a potential market launch in the second half of 2027 [26].

The vaccine targets outer surface protein A (OspA) of Borrelia burgdorferi, the same mechanism used by LYMErix — the only previous human Lyme vaccine, manufactured by SmithKline Beecham and approved by the FDA in 1998. LYMErix was voluntarily withdrawn from the market in February 2002, a story that still casts a long shadow [27].

The withdrawal was not driven by safety data. Both pre- and post-licensure studies found no difference in arthritis rates between vaccinated and unvaccinated individuals, and the FDA found no evidence of harm [27]. Instead, LYMErix collapsed under a combination of factors: unsubstantiated media reports linking the vaccine to autoimmune arthritis, class-action lawsuits (which were ultimately settled without establishing causation), vaccine hesitancy amplified by the concurrent MMR-autism scare and RotaShield withdrawal, and a critical structural vulnerability — because the Lyme vaccine was elective, it was not covered by the National Vaccine Injury Compensation Program, leaving the manufacturer directly exposed to litigation [28][27].

Could those pressures recur? VLA15 faces a different landscape. Vaccine acceptance has shifted since the COVID-19 pandemic, though in complex ways — overall willingness to receive recommended vaccines has both increased among some populations and decreased among others. The commercial calculation is also different: with 476,000 annual U.S. cases and growing public awareness, the addressable market is larger than it was in the late 1990s. But the vaccine will still be elective, and its OspA-based mechanism means it will face some of the same unfounded safety narratives that plagued LYMErix [28].

The Chronic Lyme Debate

No discussion of tick-borne disease policy is complete without addressing the most contentious question in the field: what happens to patients whose symptoms persist after standard antibiotic treatment?

The Infectious Diseases Society of America (IDSA), whose guidelines are followed by most hospitals and insurers, holds that standard antibiotic courses (typically 10–28 days of doxycycline) are sufficient for all stages of Lyme disease. Persistent symptoms, in this framework, represent a post-infectious condition — PTLDS — driven by residual inflammation or immune dysregulation, not ongoing infection. The IDSA's position cites four randomized controlled trials that found no sustained benefit from extended antibiotic treatment [29].

The International Lyme and Associated Diseases Society (ILADS), a physician organization focused on complex tick-borne illness, disputes this conclusion. ILADS argues that some patients harbor persistent infection requiring longer or repeated antibiotic courses, pointing to animal studies demonstrating bacterial persistence after treatment, patient-reported improvement on extended antibiotics, and what they describe as methodological flaws in the trials cited by IDSA — including small sample sizes, restrictive enrollment criteria that excluded the sickest patients, and endpoints that may not capture the full range of patient-reported outcomes [30].

Patient advocacy organizations, including LymeDisease.org and the Global Lyme Alliance, argue that the true burden of persistent Lyme disease is systematically undercounted. They point to the diagnostic limitations described above — ELISA sensitivity as low as 35% in early disease — as evidence that many patients are never properly identified, and that reliance on serology underestimates the population of patients with ongoing symptoms [19][31].

The IDSA's defenders counter that extended antibiotic treatment carries real risks — including Clostridioides difficile infection, antibiotic resistance, and complications from long-term intravenous access — and that endorsing prolonged treatment without evidence of benefit would harm patients [29]. They note that the randomized trials, while imperfect, represent the highest level of available evidence and that no alternative study design has demonstrated persistent infection in humans after standard treatment.

In 2022, the National Academies of Sciences, Engineering and Medicine published a report recommending that research funders increase emphasis on developing treatments for patients with lingering post-Lyme symptoms — an acknowledgment that, regardless of the mechanism, a substantial patient population is suffering without adequate therapeutic options [32]. The parallels to Long COVID have further shifted the research landscape, with more funding directed toward understanding post-infectious syndromes broadly [32].

The Research Landscape

Scientific interest in tick-borne disease has grown substantially. Academic publications on the topic peaked at 5,942 papers in 2023, up from 1,341 in 2011 — a more than fourfold increase [33]. Federal research funding has also expanded: the Congressionally Directed Medical Research Programs' Tick-Borne Disease Research Program, established through annual defense appropriations, has funded dozens of studies on diagnostics, treatment, and prevention [34].

Source: OpenAlex

Data as of Jan 1, 2026CSV

The CDC's April 2026 advisory offered straightforward guidance: use EPA-registered insect repellent, wear permethrin-treated clothing, perform tick checks, and remove attached ticks within 24 hours [1]. "Tick season is here and these tiny biters can make you seriously sick," said Alison Hinckley, a CDC epidemiologist. "The good news is you have options to help prevent tick bites... These simple steps can go a long way in protecting you and your family" [1].

Whether those simple steps — and the broader systems of surveillance, diagnosis, treatment, and prevention behind them — are adequate to the scale of the problem is the question that researchers, clinicians, patients, and policymakers continue to grapple with. With a vaccine potentially a year away, diagnostic tools that miss a third or more of early cases, prevention programs that lack evidence of real-world effectiveness, and a patient community that feels unheard, tick-borne disease in 2026 is not just an ecological story. It is a test of how well the American health care system responds to a slow-moving, complex, and growing threat.