Antigenic Shift vs Antigenic Drift- Definition and 16 Differences

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Differences Between Antigenic Shift and Antigenic Drift
Figure: Antigenic Shift vs Antigenic Drift. Image Source: Health Hearty.

Here are some differences:

S.N. Characteristics Antigenic Shift Antigenic Drift
1. Definition Antigenic shift refers to the gene recombination occurring when influenza viruses re-assort. Mutations causing minute changes in the hemagglutinin and neuraminidase antigens on the surface of the Influenza virus is termed antigenic drift.
2. Result in Forms a new sub-type (Subtype A + Subtype B –> New Subtype). Forms a new strain of the virus.
3. Genome changes Large change in nucleotides of RNA. Small mutation of RNA.
4. Results from Genome re-assortment between different subtypes. Accumulation of point mutations in the gene.
5. Change type The change is sudden and drastic. The change is gradual.
6. Virus involved One or more viruses are involved. Only one virus is involved.
7. Magnitude of change The change is large at once. Changes increase with each division cycle.
8. Relatedness of new virus The new form or subtype produced bears no similarity to the previous virus. The strains produced by antigenic drift are somewhat similar to the older strains.
9. Host range May jump from one species to another, for instance, animal to human. May infect animals of the same species only.
10. Frequency of occurrence Occurs once in a time. Occurs frequently.
11. Antigen changes The virus acquires completely new antigens—for example by reassortment between avian strains and human strains. Antigens are only mutated.
12. Virus type involved Occurs only in Influenza Virus A Occurs in Influenza Virus A, B, and C
13. Leads to Leads to pandemics. Leads to main epidemics.
14. Treatment option Difficult to treat (need new vaccine) Easy to treat (antibody and drugs available)
15. Susceptibility Everybody is susceptible to the virus after an antigenic shift, and novel influenza may thus spread uncontrollably. Some people may still be immune and some others may be partially immune to the new strain of virus thus leading to a milder illness.
16. Examples The 1968 pandemic arose when the H3 hemagglutinin gene and one other internal gene from an avian donor reassorted with the N2 neuraminidase and five other genes from the H2N2 human strain that had been in circulation.

The 1918 pandemic arose when an avian H1N1 strain mutated to enable its rapid and efficient transfer from human to human.

 The subtle mutations accumulated through antigenic drift of these subtypes (e.g., H1N1, H3N2, H5N1) give rise to different strains of each subtype.

Antigenic drift is also known to occur in HIV (human immunodeficiency virus), which causes AIDS, and in certain rhinoviruses, which cause common colds in humans. It also has been suspected to occur in some cancer-causing viruses in humans.

Read more about Antigenic Shift and Antigenic Drift from USMLE Step 1 Preparation videos and books.

References

  1. http://score99.blogspot.com/2009/05/influenza-antigenic-drift-and-shift.html
  2. http://www.usmleforum.com/files/forum/2009/1/470125.php
  3. https://microbiologyinfo.com/differences-between-antigenic-shift-and-antigenic-drift/
  4. https://www.globalsecurity.org/security/ops/hsc-scen-3_flu-antigenic.htm
  5. Lydyard, P.M., Whelan,A.,& Fanger,M.W. (2005).Immunology (2 ed.).London: BIOS Scientific Publishers.

About Author

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Sagar Aryal, PhD

Dr. Sagar Aryal is a microbiologist, researcher, and science communicator from Nepal. He is also co-founder and Research Head of the Department of Natural Products at the Kathmandu Research Institute for Biological Sciences (KRIBS), where he leads research on natural product discovery and microbial biodiversity. Dr. Aryal earned his Ph.D. in Microbiology from Tribhuvan University, Kathmandu, Nepal, in 2025, supported by a DAAD Research Grant and a University Grants Commission (UGC) Nepal Ph.D. Fellowship. His research interests include Actinomycetes, Myxobacteria, microbial taxonomy, and natural products, particularly the discovery of bioactive compounds with potential pharmaceutical applications. He isolated and identified Nocardia nepalensis, a novel bacterial species from Nepal, contributing to understanding microbial diversity in the region. Dr. Aryal has published more than 16 research articles in international journals and contributed three book chapters to established academic publications. He has presented scientific research findings and developed international research collaborations through visits to more than 18 countries across Asia, Europe, North America, and Oceania. From 2023 to 2025, he served as the American Society for Microbiology (ASM) Young Ambassador to Nepal. Since December 2025, he has served as an Editorial Board Member of Scientific Reports, a Nature Portfolio journal. In recognition of his scientific contributions, Dr. Aryal received the NAST Science and Technology Youth Award 2025 from the Nepal Academy of Science and Technology. He previously received the Frs. Locke and Stiller Research Award (LSRA) for the 2017-2018 cycle from St. Xavier's College, Kathmandu, and a Nepal Academy of Science and Technology (NAST) Research Grant for 2017-2018. Alongside his scientific career, Dr. Aryal has more than 15 years of experience in blogging, content writing, and search engine optimization (SEO).