Monitoring COVID-19 Variants in Yolo County

As the number of asymptomatic as well as symptomatic people who test positive for COVID-19 rises in Yolo County and new mask wearing guidelines are implemented, it’s important to remain vigilant and continue to get tested – even if you are fully vaccinated.

The charts below shows the latest COVID-19 variant testing results from Healthy Davis Together for Yolo County. Results are updated weekly.

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

That’s why testing, especially for people who are not yet vaccinated or who have symptoms remains so important. It is also advisable to get tested when there has been an increased risk of infection (for example, participation in a large, unmasked gathering, travel or exposure to a traveler from a region with high prevalence) to screen for new variants, particularly those that overcome vaccines. For information on where to get a free COVID-19 test or vaccine, visit our testing and vaccine pages 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 remain vigilant and follow local guidance to prevent the spread of COVID-19 and all its variants, including:

Getting vaccinated

Wearing a mask/face covering

Keeping a physical distance

Practicing good hand hygiene

Getting tested for COVID-19

Avoiding large crowds, opt for outdoors

Staying home if you feel sick

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