WASHINGTON (NEXSTAR) — While in the middle of the holiday season, health experts want Americans to stay on guard as the Omicron variant poses a risk.

“It is the most transmissible virus of COVID that we had to deal with thus far,” White House Chief Medical Advisor Dr. Anthony Fauci said.

Thursday, Fauci told the U.S. Chamber of Commerce that Americans should expect omicron to become the country’s dominant variant.

“It is predictive and has shown in reality to evade certain immune parameters,” Fauci said.

Fauci says the latest data shows booster shots help improve protection against the Omicron variant, and there is currently no need for a variant-specific booster.

“If we continue to get people vaccinated, that we will be able to counter the emerging variants that we might see as the months go by,” Fauci said.

Meanwhile, CDC officials are changing their recommendation of the Johnson and Johnson vaccine, due to the risk of rare complications, such as blood clots.

“The Jansen vaccine prevents fewer COVID-19 related hospitalizations, ICU admissions and deaths. And there are more severe health impacts from TTS and GBS after a Jansen vaccine,” Dr. Sarah Oliver, CDC Workgroup Lead, said.

The CDC advisory panel now says the mRNA vaccines from Pfizer and Moderna should be the first choice of anyone over 18.