We track COVID-19 variants in California to control the spread of the disease.

On this page you’ll find:

What a variant is

Viruses change through mutations that create new strains of virus over time. This is a normal process that happens with most viruses. We call these strains variants.

Some variants rise and then disappear. Other variants become common. Most variants do not have a meaningful impact.

Variants we’re tracking

Variants of concern

Variants of concern are likely have one or more of the following features:

  • More contagious
  • Likely to cause more severe symptoms
  • Resistant to treatment
  • More resistant to vaccines
VariantKnown differences
Delta
  • 200% increased transmission
  • Reduced antibody treatment effectiveness

Variants being monitored

Variants being monitored are seen at low levels or no longer detected. They do not pose a significant or immediate risk to the public. They are likely to have one or more of the following features:

  • Potential or known effect on treatment
  • More severe symptoms
  • Increased transmission
VariantKnown differences
Alpha
  • 50% increased transmission
  • Potential increased disease severity and risk of death
  • Minimal impact on antibody treatment effectiveness
Beta
  • 50% increased transmission
  • Reduced antibody treatment effectiveness
Gamma
  • Reduced antibody treatment effectiveness
Epsilon
  • 20% increased transmission
  • Significantly reduced antibody treatment effectiveness
Eta
  • Moderately decreased antibody treatment effectiveness
Iota
  • Significantly reduced antibody treatment effectiveness
Kappa
  • Moderately decreased antibody treatment effectiveness
Zeta
  • Moderately decreased antibody treatment effectiveness
Mu
  • Moderately decreased antibody treatment effectiveness

California follows the CDC’s variant classifications and definitions.

Vaccine effectiveness against variants

We are working to better understand how these variants respond to vaccination. Vaccines provide valuable protection against variants circulating in California.

COVID-19 vaccines are effective against variants of the virus currently circulating in the United States, including the Delta variant. We are closely following evolving information about the ability of COVID-19 vaccines to protect against variants.

Variants in California

We genetically sequence a sample of positive COVID-19 tests to determine which variant they are. This helps us understand which variants are circulating in California.

[Variant percentage chart]