What’s new in 2021

This article highlights the changes in the DeCS/MeSH vocabulary.

Totals by type of terminology

Term types language 2020 2021 Variation
amount %
Main Heading (Descriptor) terms English 34041 34294 253 0,74%
Spanish (America) 34041 34294 253 0,74%
Spanish (Spain) 34041 34294 253 0,74%
Portuguese 34041 34294 253 0,74%
Entry terms English 218803 228525 9722 2,03%
Spanish (America) 60670 66118 5448 8,98%
Spanish (Spain) 51380 56740 5360 10,43%
Portuguese 67078 74963 7885 11,75%
Qualifier terms English 77 77 0 0,00%
Spanish (America) 77 77 0 0,00%
Spanish (Spain) 77 77 0 0,00%
Portuguese 77 77 0 0,00%
Total 534403 563830 29427 5,51%

Changes for 2021

  • 277 MeSH descriptors and 12 exclusive DeCS descriptors were added
  • 17 descriptors were modified in English, of which 3 are exclusive of DeCS
  • 39 descriptors were modified in Spanish, of which 22 are exclusive of DeCS
  • 53 descriptors were modified in Portuguese, of which 36 are exclusive of DeCS
  • 17 descriptors were eliminated
  • 129 scope notes have been updated in English, Spanish and Portuguese
  • 1209 indexing annotations have been updated in English, Spanish and Portuguese

Subcategories receiving the greatest number of new descriptors:

Subcat Subcategory name Descriptor amounts
B03 Bacteria 33
B01 Eukaryota 30
E05 Investigative Techniques 22
F01 Behavior and Behavior Mechanisms 18
D12 Amino Acids, Peptides, and Proteins 15
N06 Environment and Public Health 13
C14 Cardiovascular Diseases 12
D08 Enzymes and Coenzymes 12
C23 Pathological Conditions, Signs and Symptoms 11
I01 Social Sciences 11

New descritors per category

DeCS/MeSH Tree categories Descriptor amounts
A – Anatomy 9
B – Organisms 69
C – Diseases 41
D – Chemicals and Drugs 32
E – Analytical, Diagnostic and Therapeutic Techniques, and Equipment 34
F – Psychiatry and Psychology 32
G – Phenomena and Processes 29
H – Disciplines and Occupations 5
HP – Homeopathy 0
I – Anthropology, Education, Sociology, and Social Phenomena 19
J – Technology, Industry, and Agriculture 16
K – Humanities 0
L – Information Science 3
M – Named Groups 4
N – Health Care 25
SH – Science and Health 1
SP – Public Health 11
V – Publication Characteristics 0
VS – Sanitary Surveillance 0
Z – Geographicals 0

The total is greater than the number of new descriptors because some of them occur in more than one category.

DeCS 2021 for online consultation is available through the DeCS Portal or directly from the home page of the VHL Regional Portal.

Helpful Links

For more details, please refer to these documents about the DeCS 2021 edition or the Introduction to MeSH 2021.

The complete lists of changes to the vocabulary are available on the following links:

Vocabulary changes

New descriptors

Replaced descriptors

Deleted descriptors

DeCS and MeSH tree number changes

MeSH and DeCS 2021 highlights:

SARS-CoV-2 and COVID-19 related descriptors

Since January 2020, terms related to SARS-CoV-2 and COVID-19 have been created in the MeSH Supplementary Concept Records database (SCR).

As SCR has not yet been included in the DeCS, and in order to be able to index and retrieve documents with them in 2020, these two concepts were inserted as non-preferred concepts in the two closest general descriptors, that is, Betacoronavirus and Coronavirus Infections, respectively.

The creation of descriptors depends on the number of publications in which the terms appeared in titles and abstracts. In this way, for example, SCR terms are created or promoted to descriptors in DeCS/MeSH or not. For version 2021, the following 14 descriptors were created. Some of these have moved from the 2020 SCR base to the 2021 MeSH, while others are new.

Coronavirus 3C Proteases

Coronavirus Envelope Proteins

Coronavirus M Proteins

Coronavirus Nucleocapsid Proteins

Coronavirus Papain-Like Proteases

Coronavirus Protease Inhibitors

Coronavirus RNA-Dependent RNA Polymerase


COVID-19 Nucleic Acid Testing

COVID-19 Serological Testing

COVID-19 Testing

COVID-19 Vaccines

Receptors, Coronavirus


For more details on these and other descriptors of interest to those investigating COVID-19 and SARS-CoV-2, read the NLM technical bulletin for November-December 2020.

For more information on other descriptors updated or added to DeCS/MeSH as a result of special NLM projects click here.

Access to new data fields

In this version of DeCS, the user has access to some more existing MeSH fields:

  • The unique identifier of the RDF MeSH record.
  • CAS Type 1 Name of substances, that is, the systematic name assigned by the Chemical Abstracts Service (CAS) according to the nomenclature convention of the American Chemical Society.
  • Registration Number: contains the Unique Ingredient Identifier (UNII) linked to the molecular structure of a chemical substance and/or descriptive information by the FDA Substance Registration System (SRS).
  • Related Number of substances, that is, the registration number of salts, optical isomers or versions labeled with the isotope of the substance.

Example for the four fields above: Calcimycin

  • Previous Indexing: free text field that refers to descriptors or descriptor/qualifier combinations that were used to index the concept in MEDLINE databases before creating the descriptor. Its objective is to allow users of new descriptors to find similar indexed concepts before the creation of the descriptor. Includes dates in the format (YYYY) for a single year or (YYYY-YYYY) for a range of years. It can include descriptive text that refers to a group of descriptors as “specific.” References are not currently maintained when a <DescriptorName> or <QualifierName> changes. Example: Indinavir.
  • New: In the same Registration Number field, previously only for substances, DeCS/MeSH now offers access to the unique identifier of the NCBI taxonomy of organisms (txid). This is part of a 2020 project in which this code was added to SCR class 4 organisms. This project was extended this year to organisms of the 2021 DeCS/MeSH subcategories B1 to B4. Example: SARS-CoV-2. For more information, read NCBI Taxonomy Identifiers Added to MeSH.

Other pertinent articles:

MEDLINE/PubMed Year-End Processing Activities for 2021 MeSH

2021 MeSH Headings Available in the MeSH Browser

MEDLINE data changes – 2021


Tybaert S. MEDLINE Data Changes – 2021. NLM Tech Bull. 2010 Nov-Dec;(437):e3a. Available in:

Translation and adaptation: Sector de Terminologías y Clasificaciones en Salud – TCS – BIREME/OPS/OMS

Last update: May 2021

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