Delta Variant Drives Resurgence of COVID-19 Cases and Updated Public Health Guidance

Healthy Davis Together issued the following news release today (July 30):

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Starting today, Yolo County has reintroduced its masking requirement in indoor public spaces regardless of vaccination status due to the surge in new COVID-19 cases. County officials say the mask mandate will remain in place until the new case rate falls and stays below 2.0 per 100,000 residents for seven consecutive days.

These changes are a vital step toward gaining control of the surge in new cases led by the delta variant, which is the most infectious strain yet and currently makes up 93 percent of all new cases in and around Davis. While there was a great amount of optimism that the summer would mean the end of these restrictions, public health experts are responding to the scientific reality of the pandemic.

“We are at a critical moment that calls for increased caution and care for the health of our communities,” said Sheri Belafsky, medical director for Healthy Davis Together and director of the Medical Surveillance Program in the Department of Public Health Sciences, UC Davis School of Medicine. “This includes getting vaccinated as soon as possible, getting tested regularly and following local mask guidance.” When planning activities, Yolo County residents should keep in mind the recent surge in cases and remain vigilant to stop the spread.

“We’re not out of the woods yet,” Belafsky added. “By being thoughtful and committing to the actions we know save lives, we can all help to slow the spread and reclaim the moments that matter to us most.”

Graph shows COVID-19 positivity rate falling over time, then rising from mid-July to now.
After falling from the heights seen last fall, the COVID-19 positivity rate among tests performed by Healthy Davis Together has risen sharply this summer. (UC Davis Genome Center)

Over the past month, the rate of new cases has risen eightfold while testing has declined. Test positivity rates in Davis are at their highest point since January. In that same time, hospitalizations from the virus have increased dramatically due to the high transmissibility and severity of the delta variant, which is thought to be roughly twice as contagious as the original virus strain. Recent data from the city’s wastewater sampling program also indicate higher levels of the virus that may not yet be reflected by clinical tests and may predict a continued rise in new cases.

While those who are vaccinated are at significantly less risk than those who have yet to receive the vaccine, breakthrough cases (when a fully vaccinated individual contracts the virus) account for 25-33% of all new cases, so people who are already vaccinated should also take care to follow new guidelines to protect themselves as well as decrease the possibility of spreading it to others.

“Though the recent rise in cases, both locally and nationally, may be disheartening, it’s important that our community remain committed to halting the spread of the virus and protecting the health of our friends, loved ones and neighbors,” said Brad Pollock, Healthy Davis Together project director and chair of the Department of Public Health Sciences. “A reinvigorated effort to combat the pandemic will not only save lives but also bring about a far quicker end to the need for restrictions and a faster return to normal life in Davis.”


From Healthy Davis Together

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Healthy Davis Together is a joint project of UC Davis and the city of Davis to prevent the spread of COVID-19 in our community and facilitate a coordinated and gradual return to regular city activities and student life. Comments and questions are welcome at

The UC Davis Genome Center testing lab operates under a CLIA-certified extension of UC Davis Student Health and Counseling Services’ CLIA license.

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