Monitoring COVID-19 Variants in Yolo County

As the number of asymptomatic as well as symptomatic people who test positive for COVID-19 varies by week in Yolo County and mask wearing guidelines continue, it’s important to remain vigilant and continue to get tested if you are not vaccinated, if you have symptoms or have been exposed to someone with COVID-19, and before and after traveling or gathering – even if you are fully vaccinated.

UPDATE: Starting January 2, 2022, only a sample of positive COVID-19 tests could be genotyped because of the large number of positives. The prevalence of each variant was calculated and the estimated value for each variant is reported. The actual number of samples genotyped is presented with the parenthesis next to the reported number.

As part of Healthy Davis Together’s free COVID-19 testing operations, all positive COVID-19 samples from Yolo County are routinely screened by the UC Davis Genome Center for variants, including Delta, Omicron and other variants of concern and variants of interest. The new positive COVID-19 cases in Yolo County are nearly all Delta, one of the more contagious variants of concern that is now the prevalent type though much of the country.

That’s why testing, especially for people who are not yet vaccinated or who have symptoms or have been exposed remains so important. For information on where to get a free COVID-19 test visit our testing page on this site.

How to read the variant chart:

1. Each variant is labeled with its scientific name (e.g. “B.1.1.7”) and the letter of the Greek alphabet assigned by WHO (e.g. “Alpha”).

2. Variants of concern are highlighted in red. These variants are more contagious and now make up the majority of positive cases in Yolo County.

3. Only samples up to 7-10 days ago have been sequence validated. Some samples collected in the last 7-10 days are currently classified as miscellaneous, but will be classified as a known variant after sequencing data becomes available.

Genotyping and Sequencing: Why both are important
The variants of the SARS-CoV-2 virus differ from each other at specific locations in the sequence of the viral genome. Each variant has a unique combination of specific sequence changes. Genotyping is a rapid and efficient method that looks for the presence of diagnostic changes that make each variant of concern unique. However, it does not detect changes elsewhere in the genome, and thus does not reveal the presence of new changes. Whole genome sequencing looks at every position in the viral genome and thus detects every change that is present. It is how novel variants are detected. However, it is slower and more expensive than genotyping, so in the interests of getting quick results that can be shared with the community within a few days, the UC Davis Genome Center does genotyping on all positive samples first, followed by sequencing to confirm results and reveal the presence of any new changes.

Additional Resources:
To learn more about COVID-19 variants, please visit the California Department of Public Health (CDPH) and Centers for Disease Control and Prevention (CDC).

Healthy Davis Together encourages everyone to follow local guidance to prevent the spread of COVID-19 and all its variants, including:

Getting vaccinated and getting your booster when eligible
Getting tested if you are not yet vaccinated, have symptoms or have been exposed to someone with COVID-19 and before and after traveling or gathering, even if you are vaccinated
Following local guidance on mask wearing
Staying home if you feel sick

If you have questions, please email [email protected].

Healthy Davis Together encourages everyone to remain vigilant and follow local guidance to prevent the spread of COVID-19 and all its variants, including:

Getting vaccinated and boosted

Getting tested for COVID-19

Wearing a mask/face covering

Keeping a physical distance

Practicing good hand hygiene

Avoiding large crowds

Opting for outdoors

Staying home if you feel sick

If you have questions, please email [email protected].