Definition and research guide
This page combines a MeSH definition, publication statistics and selected research abstracts. It is a starting point for reading the literature, not a medical textbook or a systematic evidence review.
Content available: 4 complete abstracts (728 words), 10 references. Full article text is not stored or reproduced here; follow the PMID, DOI or PMC links to read the original sources and their access terms.
Definition
Divisions of the year according to some regularly recurrent phenomena usually astronomical or climatic. (From McGraw-Hill Dictionary of Scientific and Technical Terms, 6th ed)
Definition: NLM Medical Subject Headings (MeSH) scope note (Public domain (U.S. National Library of Medicine); attribution requested). View the MeSH record.
Also known as: Season; Seasonal Variation; Seasonal Variations; Variation, Seasonal; Variations, Seasonal.
Where it fits in the MeSH classification
- Broader topics
- Periodicity; Climate
Research landscape
PubMed indexes 135,605 records tagged with the MeSH heading “Seasons” (counts retrieved 2026-10-31). 29,982 of them (22.1%) were published from 2020 onward, and the busiest period so far is 2010-2019 with 43,992 records.
Reviews account for 4,488 records (3.3%) and meta-analyses for 366. Randomized controlled trials number 1,158 (0.9%) as a share of all records on the topic. Randomized trials make up only a small share of this literature, so much of what is known comes from laboratory, observational or descriptive work.
Show the data
| Period | Records |
|---|---|
| through 1999 | 35,028 |
| 2000-2009 | 26,603 |
| 2010-2019 | 43,992 |
| 2020 onward | 29,982 |
Publication-type chart data
| Type | Records | Share |
|---|---|---|
| Reviews | 4,488 | 3.3% |
| Meta-analyses | 366 | 0.3% |
| Randomized controlled trials | 1,158 | 0.9% |
Method: PubMed query "Seasons"[MeSH Terms] with publication-type and date filters, retrieved 2026-10-31.
Reading the evidence in public health and nutrition
Population and nutrition studies mostly observe what people eat, breathe or are exposed to and then look for links with health, which shows association and not proof of cause. Self-reported diet is imprecise, people who eat or live differently also differ in other ways, and effects measured across a population may not apply to one person. Check the study design, how exposure was measured, what else was accounted for and the size of the effect, not only whether it was statistically significant.
Evidence from open-access studies
These open-access studies come from PubMed’s best-match results for this heading (papers whose main topic it is), ranked here by citation count, with one recent addition. Each abstract is reproduced in full under its recorded open licence so that you can read the authors’ own words. They illustrate the literature; they are not a systematic summary of it. Citation counts measure attention, not reliability or clinical benefit.
| Study / authors | Year | Source label / design | Europe PMC citations | Licence / source |
|---|---|---|---|---|
| Global phenology maps reveal the drivers and effects of seasonal asynchrony | 2025 | Research article Design not recorded in structured metadata | 9 | cc by PMID 40866701 · DOI · PMC12408380 |
| Habitat and seasonal drivers of leukocyte profiles within and across Neotropical bat species | 2025 | Research article Design not recorded in structured metadata | 7 | cc by PMID 41159440 · DOI · PMC12570079 |
| Emerging trend of increasing spring frost damage for beech at higher elevations in the Jura Mountains: evidence from tree-ring data | 2025 | Research article Design not recorded in structured metadata | 7 | cc by PMID 40827653 · DOI · PMC12445829 |
| Seasonal forcing and waning immunity drive the sub-annual periodicity of the COVID-19 epidemic | 2026 | Research article Design not recorded in structured metadata | 6 | cc by PMID 42044189 · DOI · PMC13138748 |
Global phenology maps reveal the drivers and effects of seasonal asynchrony [1]
Abstract reading summary — source excerpts
- Opening excerpt
- Terrestrial plant communities show great variation in their annual rhythms of growth, or seasonal phenology1,2.
- Closing excerpt
- Finally, we find that our global LSP map predicts complex geographical discontinuities in flowering phenology, genetic divergence and even harvest seasonality across a range of taxa, establishing remote sensing as a crucial tool for understanding the ecological and evolutionary consequences of allochrony by allopatry.
- Interpretation limits
- Verbatim excerpts from the authors’ abstract; the closing excerpt may describe a finding, limitation or recommendation. Design, population, effect size and uncertainty have not been independently extracted or appraised. Read the complete abstract and linked paper before interpreting the findings.
Read complete abstract (203 words)
Terrestrial plant communities show great variation in their annual rhythms of growth, or seasonal phenology1,2. The geographical patterns resulting from this variation, known as land surface phenology (LSP)3, contain valuable information for the study of ecosystem function4,5, plant ecophysiology6-8, landscape ecology9,10 and evolutionary biogeography11-13. Yet globally consistent LSP mapping has been hampered by methods that struggle to represent the full range of seasonal phenologies occurring across terrestrial biomes14, especially the subtle and complex phenologies of many arid and tropical ecosystems1,15,16. Here, using a data-driven analysis of satellite imagery to map LSP worldwide, we provide insights into Earth's phenological diversity, documenting both intercontinental convergence between similar climates and regional heterogeneity associated with topoclimate, ecohydrology and vegetation structure. We then map spatial phenological asynchrony and the modes of asynchronous seasonality that control it, identifying hotspots of asynchrony in tropical mountains and Mediterranean climate regions and reporting evidence for the hypothesis that climatically similar sites exhibit greater phenological asynchrony within the tropics. Finally, we find that our global LSP map predicts complex geographical discontinuities in flowering phenology, genetic divergence and even harvest seasonality across a range of taxa, establishing remote sensing as a crucial tool for understanding the ecological and evolutionary consequences of allochrony by allopatry.
Abstract reproduced from the open-access article under the recorded cc by licence; © the authors. PMID 40866701 · DOI · PMC12408380
Habitat and seasonal drivers of leukocyte profiles within and across Neotropical bat species [2]
Abstract reading summary — source excerpts
- Opening excerpt
- Land conversion is a widespread form of environmental change that can alter infection dynamics in wildlife by modifying host immune defence.
- Closing excerpt
- Our results highlight the complex, species-dependent effects of environmental change on wildlife immunity.
- Interpretation limits
- Verbatim excerpts from the authors’ abstract; the closing excerpt may describe a finding, limitation or recommendation. Design, population, effect size and uncertainty have not been independently extracted or appraised. Read the complete abstract and linked paper before interpreting the findings.
Read complete abstract (198 words)
Land conversion is a widespread form of environmental change that can alter infection dynamics in wildlife by modifying host immune defence. Such effects may be compounded by seasonal variation in resources and reproduction and differ among members of a host community, yet the combined effects of habitat, season and species identity on wildlife immunity remain poorly understood. We tested within- and across-species effects of land conversion and seasonality on immunity in Neotropical bats by quantifying haematological markers of physiological stress and inflammation. We sampled seven species across a large forest preserve and smaller nearby forest fragment in northern Belize during the dry and wet seasons. Using phylogenetic generalized linear mixed models, we tested overall effects of habitat and season and quantified per-species impacts. Total leukocyte counts and neutrophil-to-lymphocyte ratios showed no overall habitat or seasonal effects but displayed strong species-specific responses to these predictors. In contrast, the systemic inflammation response index was higher across species in the dry season and in the smaller fragment, suggesting poor health in unfavourable conditions. Species-specific effects did not align with diet guilds, indicating potential roles for finer-scale ecological traits. Our results highlight the complex, species-dependent effects of environmental change on wildlife immunity.
Abstract reproduced from the open-access article under the recorded cc by licence; © the authors. PMID 41159440 · DOI · PMC12570079
Emerging trend of increasing spring frost damage for beech at higher elevations in the Jura Mountains: evidence from tree-ring data [3]
Abstract reading summary — source excerpts
- Opening excerpt
- Late spring frost (LSF) severely impacts tree growth and forest productivity, with global warming potentially altering LSF risk due to asymmetric changes in vegetation onset and frost timing.
- Closing excerpt
- The increasing frequency of damaging LSFs raises concern about future frost risks in mountainous areas under climate change.
- Interpretation limits
- Verbatim excerpts from the authors’ abstract; the closing excerpt may describe a finding, limitation or recommendation. Design, population, effect size and uncertainty have not been independently extracted or appraised. Read the complete abstract and linked paper before interpreting the findings.
Read complete abstract (201 words)
Late spring frost (LSF) severely impacts tree growth and forest productivity, with global warming potentially altering LSF risk due to asymmetric changes in vegetation onset and frost timing. However, reconstructing past frost regimes with climatic and phenological data remains challenging. Using phenological models, high-resolution climate and tree-ring data, we identified damaging LSF on European beech at two sites in the Swiss Jura mountains over nine decades. A novel tree-ring indicator, comparing frost-sensitive beech with evergreen Norway spruce, allowed us to isolate LSF impacts from background climate signals. While no significant long-term trend in the safety margin between leaf-out and LSF was detected since 1930, negative margins - that is, leaf-out preceding last frost - were frequent at the high-elevation site in the last two decades. Our tree-ring approach identified six damaging LSF events since 1991, exceeding twice the long-term return rate. No lag effects of LSF were found, suggesting beech can tolerate episodic frosts. These findings demonstrate the potential of tree rings as bioindicators of past LSF events, offering an alternative to climatic and phenological records, which contain uncertainties that hamper LSF reconstructions. The increasing frequency of damaging LSFs raises concern about future frost risks in mountainous areas under climate change.
Abstract reproduced from the open-access article under the recorded cc by licence; © the authors. PMID 40827653 · DOI · PMC12445829
Seasonal forcing and waning immunity drive the sub-annual periodicity of the COVID-19 epidemic [4]
Abstract reading summary — source excerpts
- Opening excerpt
- Seasonal trends in infectious diseases are shaped by climatic and social factors, with many respiratory viruses peaking in winter.
- Closing excerpt
- Using a modified SIRS model that allows specification of the tempo of waning immunity, we show that specific forms of non-durable immunity can sufficiently explain the sub-annual waves characteristic of the COVID-19 epidemic.
- Interpretation limits
- Verbatim excerpts from the authors’ abstract; the closing excerpt may describe a finding, limitation or recommendation. Design, population, effect size and uncertainty have not been independently extracted or appraised. Read the complete abstract and linked paper before interpreting the findings.
Read complete abstract (126 words)
Seasonal trends in infectious diseases are shaped by climatic and social factors, with many respiratory viruses peaking in winter. However, the seasonality of COVID-19 remains in dispute, with significant waves of cases across the United States occurring in both winter and summer. Using wavelet analysis of COVID-19 cases during the pandemic period, we find that the periodicity of epidemic COVID-19 varies markedly across the U.S. and correlates with winter temperatures, indicating seasonal forcing. However, seasonal forcing alone cannot explain the pattern of multiple waves per year that has been so characteristic of COVID-19. Using a modified SIRS model that allows specification of the tempo of waning immunity, we show that specific forms of non-durable immunity can sufficiently explain the sub-annual waves characteristic of the COVID-19 epidemic.
Abstract reproduced from the open-access article under the recorded cc by licence; © the authors. PMID 42044189 · DOI · PMC13138748
Key reviews and meta-analyses
The most cited review-type papers among PubMed’s best-match results for this heading, listed with bibliographic details only. Follow the links for the full text and access terms.
- Research article Global burden of respiratory infections due to seasonal influenza in young children: a systematic review and meta-analysis [5]
- Research article The evolution of seasonal influenza viruses [6]
- Research article Air pollution and daily mortality: a review and meta analysis [7]
- Research article Respiratory Syncytial Virus Seasonality: A Global Overview [8]
- Research article Prevention and Control of Seasonal Influenza with Vaccines: Recommendations of the Advisory Committee on Immunization Practices - United States, 2024-25 Influenza Season [9]
- Research article A systematic review and meta-analysis of Northern Hemisphere season of birth studies in schizophrenia [10]
Full-text reviews on EvidenceLib
Open-access review articles about this topic, reproduced in full with authors, licence and references.
Climate factors and gestational diabetes mellitus risk – a systematic review
Emma V. Preston, Claudia Eberle, Florence M. Brown et al. · Environmental Health 2020 · CC BY 4.0
References
- Terasaki Hart DE, Bùi TN, Di Maggio L, Wang IJ. Global phenology maps reveal the drivers and effects of seasonal asynchrony. . 2025. PMID 40866701 · DOI · PMC12408380
- Becker DJ, Dyer KE, Lock LR, Fenton MB, Simmons NB. Habitat and seasonal drivers of leukocyte profiles within and across Neotropical bat species. . 2025. PMID 41159440 · DOI · PMC12570079
- Vitasse Y, Spafford L, Reim J, Baumgarten F, Martínez-Sancho E. Emerging trend of increasing spring frost damage for beech at higher elevations in the Jura Mountains: evidence from tree-ring data. . 2025. PMID 40827653 · DOI · PMC12445829
- Rubin IN, Bushman M, Lipsitch M, Hanage WP. Seasonal forcing and waning immunity drive the sub-annual periodicity of the COVID-19 epidemic. . 2026. PMID 42044189 · DOI · PMC13138748
- Nair H, Brooks WA, Katz M, Roca A, Berkley JA, Madhi SA, et al.. Global burden of respiratory infections due to seasonal influenza in young children: a systematic review and meta-analysis. Lancet. 2011. PMID 22078723 · DOI
- Petrova VN, Russell CA. The evolution of seasonal influenza viruses. Nat Rev Microbiol. 2018. PMID 29081496 · DOI
- Schwartz J. Air pollution and daily mortality: a review and meta analysis. Environ Res. 1994. PMID 8287841 · DOI
- Obando-Pacheco P, Justicia-Grande AJ, Rivero-Calle I, Rodríguez-Tenreiro C, Sly P, Ramilo O, et al.. Respiratory Syncytial Virus Seasonality: A Global Overview. J Infect Dis. 2018. PMID 29390105 · DOI
- Grohskopf LA, Ferdinands JM, Blanton LH, Broder KR, Loehr J. Prevention and Control of Seasonal Influenza with Vaccines: Recommendations of the Advisory Committee on Immunization Practices - United States, 2024-25 Influenza Season. MMWR Recomm Rep. 2024. PMID 39197095 · DOI · PMC11501009
- Davies G, Welham J, Chant D, Torrey EF, McGrath J. A systematic review and meta-analysis of Northern Hemisphere season of birth studies in schizophrenia. Schizophr Bull. 2003. PMID 14609251 · DOI
About this article
- Sources
- NLM Medical Subject Headings (definition, synonyms); NCBI PubMed (counts, identifiers); Europe PMC (open-access abstracts and citation counts).
- Verification
- Every reference was resolved against PubMed on 2026-11-04; title, year and DOI matched.
- Review state
- automated source verified; no human expert review has been recorded yet.
- Version
- 1, last updated 2026-11-04.
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Evidence strength
EvidenceHelix's computed view of the study designs behind this topic: how common meta-analyses, randomized trials and reviews are, how recent the literature is, and a plain-language reading. It describes the design mix of the literature. It is not a quality appraisal of any study, and it is not medical advice.