SARS-CoV-2 subvariant XEC: emerging challenges amidst the global decline of KP.3.1.1

Abstract

The ongoing COVID-19 pandemic has seen the emergence of numerous SARS-CoV-2 variants, each posing distinct public health challenges. The XEC variant, a recombinant Omicron subvariant, has rapidly gained prevalence globally, raising critical questions about its potential implications on health systems and public policy. This paper examines the emergence, spread, and unique characteristics of XEC, especially in the context of the global decline of KP.3.1.1, another significant Omicron lineage. We discussed the public health implications, including vaccine effectiveness, genomic surveillance, and healthcare system preparedness, underscoring the need for adaptive strategies in response to evolving SARS-CoV-2 variants.

Introduction

Over the past two decades, the world has faced an unsettling rhythm of emerging and re-emerging incidences of infectious diseases like Ebola, Zika, H5N1 avian influenza, dengue, Mpox, and Coronavirus disease 2019 (COVID-19), with each one exposing the fragility of public health systems and reminding us of our global interconnectedness and shared vulnerabilities [1–5]. The COVID-19, also known as severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) pandemic has been a relentless race with a marathon of mutations and survival. From its earliest days, the virus demonstrated remarkable adaptability, continuously evolving to outpace humanity’s defenses. Variants like Alpha, Delta, and Omicron became more than scientific names; they symbolized pivotal moments in the pandemic, each presenting new challenges that reshaped public health strategies and prompted vaccine updates.

Today, a new contender has emerged: the XEC variant. Detected across multiple countries, XEC is showing early signs of dominance, gradually outcompeting its predecessors and raising fresh questions for researchers and policymakers. Its rise coincides with the decline of KP.3.1.1, a subvariant of Omicron that once prevailed but now appears to be losing ground [6]. This shifting competition among SARS-CoV-2 lineages highlights the virus’s persistent drive for survival and humanity’s need to stay ahead.

In this paper, we examine XEC’s emergence: what distinguishes it, its impact on vaccines and public health strategies, and the broader context of its rise. As the world observes this new chapter of the pandemic, understanding XEC’s trajectory provides critical insight into the evolving battle against COVID-19 and what might lie ahead.

Epidemiological trends of SARS-CoV-2 variants and subvariants

Over the past four years, the world has witnessed the emergence and spread of multiple SARS-CoV-2 variants, leading to different Variants of Interest (VOIs) and Variants of Concern (VOCs) [6]. VOIs are characterized by genetic changes that are predicted or known to affect virus characteristics such as transmissibility, immune escape, or disease severity, and have been identified to cause significant community transmission or multiple COVID-19 clusters across countries. In contrast, VOCs demonstrate evidence of increased transmissibility, more severe disease (e.g., increased hospitalizations or deaths), significant reduction in neutralization by antibodies generated during previous infection or vaccination, reduced effectiveness of treatments or vaccines, or diagnostic detection failures. Among the notable VOCs are Alpha, Beta, Delta and Omicron and its sub-lineages, which have posed distinct epidemiological and clinical challenges throughout the pandemic. It is noteworthy that these variants have necessitated ongoing adjustments to vaccine strategies, therapeutic approaches, and public health policies globally. This underscores the importance of genomic surveillance, real-time epidemiological tracking, and robust public health preparedness frameworks to mitigate future outbreaks and inform timely interventions.

Omicron and its subvariants: the path to XEC

The Omicron variant (B.1.1.529) was first reported to the World Health Organization (WHO) from South Africa on November 24, 2021, and was rapidly designated as a Variant of Concern due to its extensive spike protein mutations [7]. This variant demonstrated increased transmissibility and notable immune escape compared to previous variants, which triggers global surges in infection rates [8]. Subsequently Omicron evolved into multiple subvariants, including BA.1, BA.2, BA.4, and EG.5 etc., each with different genetic makeup and public health impact. BA.4 and BA.5 exhibited enhanced transmissibility and partial resistance to vaccine-induced and natural immunity [9]. Other emerging descendants such as BA.2.75, XBB, and BQ.1 posed additional challenges for therapeutic interventions and vaccine updates [10].

Most recently, KP.3.1.1, a subvariant of Omicron, rose to dominance in early 2024 across Europe and North America, driven by its notable immune escape capabilities and moderate transmissibility [13]. However, its reign has been short-lived, as it is now being overtaken by emerging variants such as XEC, which display a pronounced growth advantage. This transition underscores the dynamic and competitive nature of SARS-CoV-2 evolution. The XEC subvariant which is a recombinant lineage derived from KS.1.1 and KP.3.3 has been detected in several countries, including Germany, where it was first reported in July 2024. Early genomic assessments suggest XEC may combine transmissibility and immune evasion characteristics of its parent lineages, though more research is required to understand its clinical significance [11, 12]. Its emergence further reinforces the importance of sustained genomic surveillance and adaptive public health preparedness [14] (Fig. 1).

Fig. 1.

Timeline of the SARS-CoV-2 variants and subvariants

Competitive dynamics

Several factors contribute to XEC’s ability to outcompete KP.3.1.1:

1. Enhanced Transmissibility: XEC’s recombinant nature provides a fitness advantage, enabling faster spread [15].

2. Superior Immune Evasion: Mutations like Q493E allow XEC to bypass neutralizing antibodies generated by prior infections or vaccinations more effectively than KP.3.1.1 [14].

The decline of KP.3.1.1 highlights the dynamic interplay of evolutionary pressures that Favor variants with greater adaptability to host immune responses and transmission dynamics.

Understanding the XEC variant

Origin and classification

In the evolving trend of SARS-CoV-2, the XEC variant represents a story of convergence and adaptation, reflecting the virus’s remarkable evolutionary flexibility. As a recombinant lineage, XEC emerged from the genetic melding of two distinct parental variants, KS.1.1 and KP.3.3, both descendants of the globally dominant JN.1 variant. Genetic recombination, the process underlying XEC’s creation, occurs when multiple viral lineages simultaneously infect a single host, allowing their genetic material to intermix and produce a novel variant [15].

XEC was first identified in Germany during the summer of 2024. Initially spreading unnoticed, it quickly crossed borders and continents. By November, it had been detected in 27 countries and accounted for 36.8% of all global SARS-CoV-2 sequences [1]. Its prevalence was highest in Europe, with Germany as the epicentre, where nearly 13% of sequenced cases bore its genetic signature. The United Kingdom reported a prevalence of 7%, while the United States remained below 5%.

As the Northern Hemisphere’s winter looms, XEC appears poised to assume global dominance, its growth advantage positioning it as a leading variant [13]. The emergence of XEC underscores SARS-CoV-2’s relentless capacity for evolution and adaptation, serving as a stark reminder of the pandemic’s unyielding progression.

In contrast, KP.3.1.1, a previous dominant Omicron descendant, witnessed a global decline despite accounting for over 50% of new COVID-19 cases in the United States as of mid-2024. Several factors have contributed to this downturn. First, the emergence of competitive variants notably XEC may have led to selective displacement due to superior transmissibility or immune escape potential [16, 17]. Second, increasing population immunity through vaccination campaigns and widespread natural infections has reduced the number of individuals susceptible to infection [18]. Finally, ongoing public health interventions, such as updated vaccine boosters, widespread testing, and non-pharmaceutical interventions (NPIs), have played a key role in limiting the spread of KP.3.1.1 [19].

A comparative analysis of XEC and other Omicron subvariants reveals both similarities and differences. Genetically, XEC is a recombinant hybrid, unlike single lineage subvariants such as BA.2 or BA.5, as it combines mutations from two separate Omicron offshoots KS.1.1 and KP.3 [116]. This unique origin may contribute to changes in viral behavior, though its full impact is still under investigation. Regarding immune evasion, early data suggest that XEC exhibits antibody escape properties on par with, or slightly exceeding, those of its parent strains [217]. Clinically, however, XEC remains comparable to other Omicron subvariants, with most infections presenting as mild to moderate illness [16].

Genetic and phenotypic characteristics

XEC’s genetic profile includes key mutations that enhance its transmissibility and immune evasion. Notably:

• T22N mutation (from KS.1.1): Associated with structural changes in the spike protein, potentially increasing transmissibility [20].

• Q493E mutation (from KP.3.3): Alters the receptor-binding domain, contributing to immune escape by reducing antibody neutralization efficiency [14].

While its symptoms remain consistent with other Omicron sub variants—fever, sore throat, cough, and fatigue—its transmissibility and ability to evade prior immunity make it a significant public health concern [13].

Is the current vaccine effective against XEC?

Vaccines targeting earlier Omicron lineages, such as JN.1 and KP.2, remain effective at preventing severe disease and hospitalization caused by XEC. However, its immune escape potential may reduce vaccine efficacy against infection and mild disease [20, 21].

The updated 2024–2025 COVID-19 vaccines, tailored to JN.1 and KP.2, are likely to provide substantial protection against severe outcomes associated with XEC. For example, the United Kingdom’s autumn booster campaign, emphasizing updated formulations, aims to mitigate hospitalizations during the winter surge [22].

The need for adaptation

The emergence of the XEC variant underscores the necessity for continuous adaptation in combating SARS-CoV-2. As the virus evolves, so too must our strategies, particularly the timely development and distribution of variant-specific vaccines. Accelerating these efforts is essential to sustain immunity and mitigate the impact of future variants [13].

XEC’s emergence serves as a poignant reminder of the pandemic’s central lesson: adaptability is vital. The virus’s relentless evolution demands a dynamic response that prioritizes the development and equitable distribution of variant-specific boosters. Beyond scientific necessity, this is a public health imperative. By staying ahead of emerging variants, the global community can reduce the severity of future waves, protect those most at risk, and reinforce preparedness in the ongoing race against viral evolution.

Public health implications

Hospitalization and disease severity

The emergence of the XEC variant marks a new chapter in the evolving narrative of SARS-CoV-2, with significant implications for global public health systems. Although definitive clinical data on XEC’s disease severity remains limited, its genetic similarity to other variants suggests it may cause typical COVID-19 symptoms, including fever, sore throat, cough, fatigue, and body aches [13]. Its spread coincides with winter in many regions, a period historically linked to increased hospitalizations from respiratory illnesses. Colder temperatures and more frequent indoor gatherings provide an ideal setting for viral transmission, likely amplifying the seasonal surge. However, it is essential to contextualize rising hospitalizations within the broader landscape of respiratory viruses and SARS-CoV-2 evolution to accurately assess XEC’s impact among other contributing factors.

Monitoring and surveillance

Effective management of XEC requires robust genomic surveillance. Platforms like Global Initiative on Sharing all Influenza Data (GISAID) have been invaluable in tracking variants and analysing their genetic evolution [23]. Yet, disparities in sequencing capacity, particularly in low- and middle-income countries, hinder timely variant reporting and threat identification. Strengthening global collaboration and investing in sequencing infrastructure are critical for equitable and efficient monitoring. Enhanced genomic surveillance will enable swift adaptation of public health measures to changes in transmissibility, vaccine efficacy, or disease severity.

Health system strain

As XEC spreads, it could exacerbate strain on healthcare systems, especially in regions with low vaccination rates or limited resources [24]. Public health systems must scale up testing, contact tracing, and vaccination efforts to control the variant’s spread. Healthcare workers, already under immense pressure, require sustained support through adequate staffing, protective measures, and resources to prevent burnout and maintain care delivery. In cases where there are staff shortages, non-medical personnels must be targeted for training in emergencies [25].

Potential for future variants

XEC’s rise serves as a stark reminder of the unpredictable nature of SARS-CoV-2 evolution. Recombinant variants, such as the T22N-carrying MV.1, are already under observation, and XEC itself may spawn subline ages with enhanced transmissibility or immune evasion [20]. These developments emphasize the ongoing need for vigilant surveillance, innovative vaccine strategies, and proactive public health measures.

Addressing the emerging threats

The XEC variant’s emergence signifies a pivotal moment in the SARS-CoV-2 pandemic. As KP.3.1.1, a once-dominant Omicron subvariant, declines, XEC leverages its higher transmissibility and immune evasion capabilities to dominate during the winter of 2024–2025. This transition emphasizes the virus’s adaptability and its relentless drive to exploit immunity gaps. While updated vaccines targeting earlier Omicron lineages offer robust protection against severe outcomes, uneven surveillance and healthcare capacities threaten the global response.

To manage XEC and future variants effectively, five critical strategies must take precedence:

Continuous genomic monitoring

Early identification of emerging threats is essential for timely public health interventions. Platforms like GISAID have been instrumental but require further investment to close gaps in global sequencing capacity, particularly in under-resourced regions. Equitable access to genomic data is crucial for a coordinated response.

Rapid vaccine adaptation

mRNA platforms provide flexibility for quickly updating vaccine formulations to match evolving variants. However, innovation alone is insufficient. Proactive distribution and equitable access to updated vaccines, especially in vulnerable regions, are imperative to sustain global immunity.

Equitable resource distribution

Strengthening healthcare systems through investments in testing infrastructure, vaccination campaigns, and healthcare worker support is vital. These measures will alleviate strain on health systems during high-risk periods like winter and fortify global preparedness against future variants.

Harnessing technology and community empowerment

To revolutionize public health efforts, leveraging digital tools and localized interventions should become a priority. Social media platforms like Instagram, TikTok, and Facebook can be harnessed to deliver timely messages on XEC prevention through pop-up ads, short videos, and interactive content. Mobile health platforms could also play a key role by providing reminders about testing, vaccinations, and safety protocols while connecting users to telehealth services and clinics. Establishing mobile clinics in underserved regions would help bridge healthcare access gaps, ensuring that vulnerable populations receive essential services.

Community empowerment must remain at the heart of this response. Governments and organizations should support local leaders to transform schools, markets, and community centres into health hubs where residents can learn about self-testing and access reliable vaccine information. These grassroots initiatives could foster ripple effects as informed individuals become ambassadors within their communities, spreading awareness and encouraging action. Cities like Bogotá, Nairobi, and Jakarta offer models for how localized efforts can empower communities while simultaneously contributing to global genomic surveillance systems.

Strengthening global collaboration

At both national and international levels, fostering coordinated efforts will be essential. Governments and organizations should consider subsidizing testing kits, vaccines, and mobile health services to ensure that no community is left behind. Increasing investments in healthcare infrastructure, particularly in low- and middle-income countries, is critical to building resilience against current and future variants.

Global genomic surveillance initiatives, such as GISAID, require sustained support to address disparities in sequencing capacity and ensure the early detection of new threats. Strengthening these systems would enable timely updates to public health measures, including vaccine adaptations.

The emergence of XEC underscores the virus’s relentless adaptability, reinforcing the need for a united global response. By prioritizing vigilance, equitable resource distribution, and innovative public health strategies, the global community can better prepare for and mitigate the impact of evolving variants. These efforts, when implemented, have the potential to strengthen public health systems and foster a more secure and equitable future.

Conclusion

The emergence of XEC highlights the virus’s relentless adaptability and the urgent need for a unified, innovative response. Rapid vaccine adaptation is essential to address immune evasion, while collaborative research must drive the development of next-generation vaccines. However, the fight against XEC extends beyond laboratories it is a collective effort, requiring individuals, communities, and nations to work together to safeguard public health. Through sustained vigilance, the integration of advanced technology, localized interventions, and global solidarity, humanity can meet the challenge of XEC and build resilience against future variants. This moment is not just about combating a virus it is an opportunity to transform how we address shared health crises.

Author contributions

SA, HC and OCE: conceptualized and wrote the manuscript, contributed to the critical revision of the manuscript.SA, HC and OCE: wrote the manuscript, contributed to the critical revision of the manuscriptAll authors read and approved the final manuscript.

Funding

No specific funding was received for the writing of this commentary.

Data availability

No datasets were generated or analysed during the current study.

Declarations

Ethics approval and consent to participate

Not applicable.

Consent for publication

Not applicable. No individual data is presented in this manuscript.

Competing interests

The authors declare no competing interests.