This illustration, created at the Centers for Disease Control and Prevention (CDC), reveals ultrastructural morphology exhibited by coronaviruses. Note the spikes that adorn the outer surface of the virus, which impart the look of a corona surrounding the virion, when viewed electron microscopically. A novel coronavirus, named Severe Acute Respiratory Syndrome coronavirus 2 (SARS-CoV-2), was identified as the cause of an outbreak of respiratory illness first detected in Wuhan, China in 2019. The illness caused by this virus has been named coronavirus disease 2019 (COVID-19). (Courtesy Alissa Eckert, MSMI / Dan Higgins, MAMS via CDC 2019)

The first two known cases of the infectious B.1.117 U.K. variant of COVID in Contra Costa County have been confirmed by laboratory results, county health officials said Tuesday.

The variant, believed to have originated in the United Kingdom, is more contagious than others and possibly more deadly, officials said.

“This is a reminder that even though COVID numbers are falling, we need to continue using all our tools to prevent another surge: wear masks in public, continue to physically distance, avoid both indoor and large gatherings, and get vaccinated when it’s your turn,” Dr. Chris Farnitano, the county’s health officer, said in a statement.

Farnitano said there are likely many more in the community that have not been detected. “We can’t say how widespread it is in Contra Costa, but it’s concerning,” he said.

Farnitano said the South African variant, which has also raised concern, has not been detected in Contra Costa yet, but that it should be assumed it is also circulating in California.

The U.K. variants were discovered as part of laboratory surveillance work during the pandemic, officials said. “One local person infected with the U.K. variant began displaying common COVID-19 symptoms such as cough and muscles aches and was able to isolate at home,” officials said in a news release. “The other Contra Costa resident reported having multiple symptoms, including runny nose, cough, headache and loss of smell and taste.”

Contra Costa data and COVID-19 health information is available online at cchealth.org/coronavirus.