New-onset allergic diseases after SARS-CoV-2 infection: mechanistic hypotheses and emerging strategies for risk...

Multinational cohort studies consistently associate SARS-CoV-2 infection with elevated incidence of allergic diseases, with hazard ratios of 2.25 for asthma and 1.23 for allergic rhinitis persisting beyond six months post-infection; whether this excess risk reflects de novo allergic sensitization or preferential unmasking of pre-existing subclinical atopy remains to be established. Yet mechanisms bridging acute viral illness to delayed allergic phenotypes remain incompletely understood. This review synthesizes recent advances across epithelial biology, immunology, and neuroimmune interactions to propose a unified mechanistic framework organized around three interconnected axes. First, epithelial injury during COVID-19 triggers passive IL-33 release while inducing active TSLP and IL-25 production. These alarmins act through mechanistically distinct pathways to converge on type 2 immune priming, which is established and reinforced by epigenetic memory in group 2 innate lymphoid cells and dendritic cells. Second, regulatory T cell depletion and, hypothetically, hematopoietic stem and progenitor cell epigenetic reprogramming driven by acute interleukin-6 elevation may generate immune cell progeny with persistently altered inflammatory responsiveness, while dendritic cells adopt Th2-polarizing phenotypes that lower the threshold for allergic sensitization; the direct contribution of hematopoietic reprogramming to Th2-skewed allergic outcomes remains to be demonstrated. Third, mast cells undergo direct spike protein-mediated activation via angiotensin-converting enzyme 2 receptors, and alarmin-primed mast cells establish bidirectional crosstalk with sensory neurons that amplifies neuroinflammation and links long COVID symptoms to heightened allergic susceptibility. Together, these axes define a post-infectious vulnerability window during which allergen encounters trigger exaggerated type 2 responses. Risk stratification incorporating disease severity, circulating biomarkers including immunoglobulin E and eosinophil counts, and genetic susceptibility variants may identify individuals requiring targeted surveillance, while mechanistically informed interventions such as low-dose interleukin-2, mast cell stabilizers, and alarmin-targeted biologics warrant prospective evaluation in convalescent cohorts.