Six cases of the omicron variant have been detected in Nebraska, health officials announced.

The first individual was likely exposed during travel to Nigeria, officials said. The individual returned to the U.S. on Nov. 23 and developed symptoms the next day.

The five other people were "likely exposed" through household contact with the first case, health officials said.

Only one of the six individuals was vaccinated, officials noted, and none have required hospitalization.

-ABC News' Arielle Mitropoulos

Daily COVID-19-related hospital admissions have jumped by 26% since the beginning of November, according to federal data.

Nearly 60,000 patients with COVID-19 are currently in hospitals.

The Northeast and the Midwest are seeing the biggest jump in cases and hospitalizations, according to federal data.

-ABC News' Arielle Mitropoulos

With several cases of the omicron variant confirmed in the United States, officials have learned that "many" of those infected are vaccinated against COVID-19, according to Dr. Rochelle Walensky, director of the Centers for Disease Control and Prevention.

But many of the patients experiencing mild symptoms from omicron are also vaccinated, Walensky said, indicating that the current COVID-19 vaccines are fending off severe disease.

"We've seen omicron in about five states now and we're continuing to do investigations in other states as probable cases emerge. But what we can say, based on what these cases are showing -- some have mild disease, some may have more severe disease, many of them are vaccinated -- and what we're seeing now is that many of the people with mild disease were the vaccinated people," Walensky told ABC News' Cecelia Vega in an interview Friday on "Good Morning America."

"So we still have a lot of science to do to understand how these vaccines are working against omicron, except to say that we know for every variant that we've had it's better to be vaccinated than unvaccinated," she added.

Walensky emphasized that, despite the global frenzy around omicron, delta remains the dominant variant in the U.S.

"We have 90,000 new cases of COVID-19 every day and about 99.9% of them continue to be delta," she said. "So we can't lose sight of the fact that the vast majority of what we have here in the United States is delta, and we know how to tackle delta with vaccines, with boosters, with masking and all of our prevention measures we have been using all along."

Walensky acknowledged that there are still many unknowns about omicron, including the severity of disease, transmissibility and vaccine effectiveness.

"I think we really do need to follow the science here and understand how our vaccines are going to work against omicron," she said. "It may very well be that our vaccines actually work quite well and continue to work quite well against severe disease, and those are the studies that are ongoing."

Hawaii became the fifth state to detect the omicron variant, after confirming a case through expedited genomic sequencing Thursday, health officials said.

The individual is an unvaccinated resident of Oahu who had a previous COVID-19 infection, the state health department said. The person is experiencing "moderate symptoms," the department said.

The resident has no recent travel history, indicating that this is a case of community transmission, health officials said.