Marian Natividad, 11, gets her first COVID-19 vaccine at Katherine R. Smith Elementary School in San Jose, Calif., on Nov. 4, 2021. (Harika Maddala/ Bay City News)

Santa Clara County health officials urged residents Thursday to get a booster vaccine dose if they are eligible, forecasting a wave of cases in the coming weeks tied to the omicron variant.

Ten cases of the variant have been confirmed in the county so far, according to county Health Officer and Public Health Department Director Dr. Sara Cody.

Of those 10, four were unvaccinated, five were fully vaccinated and had yet to receive a booster and one had received a booster dose, but had not yet eclipsed the two-week period it takes for vaccine-induced protection to reach its peak.

In addition, most of those 10 have shown symptoms, Cody said, but none have required hospitalization. Early research has found that the variant may be highly contagious but less likely to cause serious illness than past variants such as delta.

Cody argued that while delta remains the county’s dominant variant, the omicron variant’s ongoing spread in Europe is likely a harbinger of the pandemic’s next phase in the Bay Area.

“When I look around the corner ahead, what I see is a deluge of omicron,” Cody said Thursday during a briefing on the variant. “What I see is perhaps one of the most challenging moments that we’ve had yet in the pandemic.”

Cody and county Vaccine Officer Dr. Marty Fenstersheib said that while the county’s vaccination rate is high — 80 percent of all county residents have completed their initial vaccine series — the original two-dose Pfizer and Moderna series or the single-dose Johnson & Johnson vaccination will likely not be enough on their own to counter the infectiousness of new variants like omicron.

However, only 44 percent of the county’s adults have received a booster dose. In addition, some 250,000 residents age 50 and up — who Fenstersheib noted are at the highest risk of infection and serious illness — have yet to receive a booster dose.

While some children between the ages of 12 and 15 would also be eligible for a booster dose if state and federal regulators had given their blessing, Fenstersheib argued those at highest risk should be prioritized first.

“Before we worry about going younger, let’s get those 250,000 adults boosted so that we can keep them from getting hospitalized or dying,” he said.

All residents age 16 and up are eligible for a booster vaccine dose if they are at least six months past their second Pfizer or Moderna dose or at least two months past their single Johnson & Johnson dose.

While the three available vaccines remain highly effective at preventing serious COVID-19 illness and death, public health officials at all levels have argued that their protection begins to wane after several months, and that preemptively boosting a person’s immune response will maximize protection against existing and potential variants of the virus, which could continue to become more contagious and even circumvent vaccine protections.

“What we’re saying is that the initial vaccine series that 80 percent of our population have gotten isn’t enough anymore because the situation on the ground has changed,” Cody said. “And so to be fully up to date with COVID vaccine protection, you need to have a booster.”

The two officials suggested that residents take extra precaution if they hold gatherings with friends and family members for the holidays by wearing a mask and getting tested prior to attending any gatherings.

Vaccination, however, remains the best tool to prevent transmission of the virus and is even more effective when paired with other mitigation measures like masking and proper ventilation for enclosed spaces.

“This is about layers of prevention; no single strategy works,” Cody said. “We have to combine them.”

Cody also acknowledged the pandemic fatigue that many are facing after cooperating with pandemic restrictions and requirements for nearly two years.

“I think what makes this so difficult is … we now have a variant that all evidence suggests grows really fast and takes over really fast,” she said. “And it’s happening in a setting where we’re (saying) ‘we’ve been at this for two years, we’re awfully tired, please don’t tell us to do anything else.’ That is how we all feel. So that combination is really challenging.”