After seeing surges in places with similar vaccination numbers in Europe as their own county, they worry it could happen here.
Omicron's emergence is changing the outlook for Santa Clara County Health Director Dr. Sara Cody.
RELATED: Santa Clara Co. reports 1st omicron case in person who traveled to Florida
Fully masked, not even taking it off to answer questions, Dr. Cody delivered a concerning message after seeing cases rise worldwide.
"When I look around the corner ahead, what I see is a deluge of omicron," Dr. Cody said. "What I see is perhaps one of the most challenging moments that we've had yet in the pandemic."
And COVID concerns are only getting greater, at a testing site in San Carlos people were lined up Thursday night to see if they have COVID.
VIDEO: Omicron COVID outlook grim as 10 new cases confirmed in Santa Clara County
Omicron is now present at some level throughout the county, according to detections in four sewer-sheds.
Ten confirmed cases include four unvaccinated individuals, five vaccinated and one person who recently got a booster.
These numbers are expected to grow.
VIDEO: Triple threat: What happens if you contract delta, omicron and the flu?
"What we think is going to happen is a big omicron wave surge on top of delta," Dr. Cody said. "We recommend booster shots for everyone who is eligible."
Only 44% of residents 18 and older in Santa Clara County are boosted, and county health officer Dr. Marty Fenstersheib says early data shows positive results against omicron.
"Especially looking at Pfizer, the effectiveness against omicron was about 30%," Dr. Fenstersheib said. "When you boosted that person, the effectiveness went up to 75% at least. The vaccines work, it's just that we need to boost them so that we have more of it on board."
Dr. Fenstersheib says the older the individual the more important the booster is. He says currently in Santa Clara County there are 250,000 adults 50 or older who have not gotten the booster and need to do so for their own health.
Even so, Dr. Cody says vaccines and boosters may still not be enough to stop omicron.
Masking, testing, ventilation and distancing are all strongly encouraged.
RELATED: Santa Clara Co. 'not anywhere near' lifting indoor mask mandate
"This is about layers of prevention," Dr. Cody said. "No single strategy works, we have to combine them."
Dr. Cody recognizes frustrations of the community, but says we are at a crossroads.
"Everyone has experienced a lot of change, a lot of uncertainty and, in a lot of cases, a lot of difficulty. That is the reality that we have. However, we can't simply lay down or put our head in the sand. When I look around the corner, I see a whole lot of omicron."
Stanford University also just announced that all students in winter courses who are eligible for the booster shot, must have it by January 31.