Why do we need an updated vaccine?

Viruses evolve.1 It’s the reason your doctor recommends you get a flu shot annually.2

Virus evolution, or “drift,” means that small changes, or “mutations,” in the virus result in changes to proteins on the surface of the virus.1,3,4 The COVID virus spike proteins attach themselves to human cells and cause infection – so it’s important for your body to be able to recognize them in order to train your immune system to fight off infection.5

As the virus that causes COVID drifts or mutates, new variants are created.1,4 Some may spread more easily, some are more resistant to previously developed vaccines, and others can be both!4 Your immune system may have trouble recognizing the new COVID variants, increasing your risk of reinfection (i.e., getting sick again).3,6

In 2020 when COVID was on the rise, the strain that caused the disease was known as the Wuhan strain.The virus that causes COVID then drifted or mutated to produce new strains, including the Alpha, Beta, Delta and Omicron strains.4 The primary strains we are dealing with as of Fall 2023 are XBB subvariants.8

For this reason, U.S. and EU public health authorities, as well as the World Health Organization, are updating their recommendations on what vaccines are needed to best combat and protect against COVID.9,10,11 These recommendations are based on extensive monitoring and data from public health agencies, industry and academia, and allow us to identify the COVID strain expected to cause the most infections in the upcoming fall season.10,12,13Vaccine manufacturers then prioritize the identified strain, developing and producing updated vaccine doses that can help immune systems around the world be better prepared against the identified variant.12,13

  1. Markov, et al. Nat Rev Microbiol. 2023;21(6):361-379.
  2. CDC. How flu viruses can change: “drift” and “shift”. Available at: https://www.cdc.gov/flu/about/viruses/change.htm#print. [Accessed: August 2023].
  3. CDC. Science Brief: COVID-19 Vaccines and Vaccination. Available at: https://www.cdc.gov/coronavirus/2019-ncov/science/science-briefs/fully-vaccinated-people.html. [Accessed: August 2023].
  4. CDC. SARS-CoV-2 Variant Classifications and Definitions. Available at: https://www.cdc.gov/coronavirus/2019-ncov/variants/variant-classifications.html. [Accessed: August 2023].
  5. CDC. Myths and Facts about COVID-19 Vaccines. Available at: https://www.cdc.gov/coronavirus/2019-ncov/vaccines/facts.html. [Accessed: August 2023].
  6. Antonelli M, et al. Risk factors and disease profile of post-vaccination SARS-CoV-2 infection in UK users of the COVID Symptom Study app: a prospective, community-based, nested, case-control study. Lancet Infect Dis. 2022;22(1):43-55.
  7. Wolf JM, et al. Molecular evolution of SARS-CoV-2 from December 2019 to August 2022. J Med Virol. 2023;95(1):e28366.
  8. CDC. Variant Proportions [Data set]. Available at: https://covid.cdc.gov/covid-data-tracker/#variant-proportions. [Accessed: August 2023].
  9. FDA. Updated COVID-19 vaccines for use in the United States beginning in fall 2023. Available at: https://www.fda.gov/vaccines-blood-biologics/updated-covid-19-vaccines-use-united-states-beginning-fall-2023. [Accessed: August 2023].
  10. EMA. EMA and ECDC statement on updating COVID-19 vaccines to target new SARS-CoV-2 virus variants. Available on: https://www.ema.europa.eu/en/news/ema-ecdc-statement-updating-covid-19-vaccines-target-new-sars-cov-2-virus-variants. [Accessed: August 2023].
  11. WHO. XBB.1.5 updated risk assessment. Available at: https://www.who.int/docs/default-source/coronaviruse/20230620xbb.1.5.pdf?sfvrsn=fff6f686_3. [Accessed: August 2023].
  12. FDA. Recommendation for the 2023-2024 Formula of COVID-19 vaccines in the U.S. Available at: https://www.fda.gov/media/169591/download?attachment. [Accessed: August 2023].
  13. WHO. Statement on the antigen composition of COVID-19 vaccines. Available at: https://www.who.int/news/item/18-05-2023-statement-on-the-antigen-composition-of-covid-19-vaccines. [Accessed: August 2023].
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