The new three cases were detected Thursday in residents by the county's health and human services department.
Officials said all three residents were vaccinated with two doses, but did not report receiving the booster shot. The cases reported mild symptoms and said they had not traveled in the last 14 days.
"While the full impact of omicron is not currently known, we do already know how to reduce the spread of any form of SARS CoV-2," said Dr. Jacquelyn Minter, the director and health authority for Fort Bend County Health & Human Services. "We can protect ourselves and those at highest risk by getting vaccinated, including with boosters, staying away from others when we are ill, getting tested when appropriate, and wearing face coverings indoors or at crowded events with close contact."
Earlier in the day, Houston Methodist Hospital confirmed nine cases of the variant.
SEE RELATED STORY: Houston Methodist Hospital confirms 9 omicron COVID-19 cases
In addition, Harris County confirmed its first case of the omicron variant spreading in the area on Monday.
READ MORE: Woman tests positive for omicron variant in NW Harris County, judge says
Woman tests positive for omicron variant in NW Harris County
Houston Methodist identified the nine cases through comprehensive genome sequencing. This is the first time since earlier this year that a variant, other than delta, has been detected by their scientists.
The hospital did not say where the patients are from, how they're doing or if they're hospitalized.
Scientists around the globe are rushing to gather more information about the new variant.
Early data suggests that omicron is less severe than the delta variant, but is much more transmissible.
SEE ALSO: 8 of 39 Houston wastewater plants detect COVID omicron variant
COVID omicron variant found in 8 Houston wastewater plants
ABC Chief Medical Correspondent Dr. Jen Ashton spoke with CDC Director Rochelle Walensky about the new variant and what doctors are hoping to discover.
"We are following and interested in increased transmissibility. We are seeing that coming from data from other countries. We are interested in disease severity," Walensky said. "Will this variant evade our vaccines and therapeutics?"
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