COVID-19 variants | Coronavirus | UC Davis Health

COVID-19 variants

Updated: Sept. 11, 2023

Throughout the past several years of COVID-19, the virus has mutated into different strains, including delta and omicron. Our infectious disease experts provide up-to-date information on the COVID variants, including symptoms and how effective the vaccines are at protecting you and your family.

  • BA.2.86 and EG.5

    Late summer 2023 saw a rise in COVID-19 hospitalizations caused by variants BA.2.86 (Pirola) and EG.5 (Eris). Our chief of infectious diseases answers questions about the new variants and the new COVID-19 boosters.

    Learn about these variants and new boosters
  • XBB.1.5 variant

    In December 2022, a new variant called XBB.1.5 emerged and quickly grew as the dominant strain into January 2023. This COVID mutation, also known as the "Kraken" variant, is causing similar COVID symptoms in 2023 as other recent strains.

    Learn more about the XBB.1.5 variant
  • Omicron variant

    The omicron subvariant of COVID-19, called BA.5, became one of the dominant strains of the virus in the U.S. in the fall of 2022. During that time, it was the most easily spread strain to date and was able to evade immunity from past COVID infection and vaccination.

    Learn more about the omicron variant
  • Delta variant

    The delta variant began spreading rapidly in the U.S. in June 2021. It was causing similar COVID symptoms, but physicians were seeing people get sicker quicker, especially younger people.

    Learn more about the delta variant
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