The University of Texas Southwestern Medical Center has identified its first omicron variant case using genomic sequencing — bringing the number of omicron cases to at least four in North Texas.

The Texas Department of State Health Services verified the case Monday, UT Southwestern spokesperson James Beltran said. The UT Southwestern lab declined to share details of the case, including where the patient is from and when the person was diagnosed with COVID-19.

The omicron variant, first detected by scientists in South Africa, appears to have more than 30 mutations in the coronavirus’ spike protein, which could affect how easily it spreads. Experts say omicron now accounts for more than 90% of all new infections in South Africa.

It now makes up about 3% of cases sequenced in the U.S., according to data from the Centers for Disease Control and Prevention. While the delta variant still dominates the U.S. with about 97% of all COVID-19 cases analyzed, omicron is quickly gaining ground, CNBC reported.

The Washington Post reported that the omicron variant is rapidly spreading in the U.S. and could peak in a massive wave of infections as soon as January, according to new modeling from the CDC.

The prevalence of omicron jumped sevenfold in a single week, CDC modeling shows. The highly mutated variant could increase pressure on a health system already strained by the delta variant, The Washington Post reported.

Of the positive COVID-19 tests that UT Southwestern sequences, about one-third come from outpatient drive-through testing, one-third come from emergency room visits and one-third come from outside clients, said Dr. Jeffrey SoRelle, who is leading UT Southwestern’s COVID-19 variant tracking effort.

All of the medical center’s sequenced COVID-19 tests come from North Texas, he said.

Denton County Public Health also announced its first omicron case Tuesday. The patient lives in Fort Worth and had recently traveled within the U.S., the county health department said in a statement. “The omicron variant test result here in Denton County underscores what we already know: COVID-19 remains an ongoing pandemic, and Denton County has continuing risk,” said Dr. Matt Richardson, DCPH director.

Last week, two cases of the omicron variant were detected in North Texas, just days after Texas’ first case was confirmed in Harris County. Frisco-based Ayass Bioscience identified the cases, and the Texas Department of State Health Services, which investigates and verifies variant cases, confirmed them Thursday.

Experts expected the spread of the new COVID-19 strain, said Dr. James Cutrell, associate professor of medicine in the Department of Infectious Diseases and Geographic Medicine at the UT Southwestern.

New omicron developments in South Africa

The omicron variant appears to cause less severe disease than previous versions of the coronavirus, and the Pfizer vaccine seems to offer less defense against infection from it but still good protection from hospitalization, the Associated Press reported. That’s according to an analysis of data from South Africa, where the new variant is driving a surge in infections.

While the findings are preliminary and have not been peer-reviewed — the gold standard in scientific research — they line up with other early data about omicron’s behavior, including that it seems to be more easily transmitted, the AP reported.

A two-dose Pfizer/BioNTech vaccination appeared to provide just 33% protection against infection during South Africa’s current omicron wave, but 70% protection against hospitalization, according to the analysis conducted by Discovery Health, South Africa’s largest private health insurer, and the South African Medical Research Council.

The data were gathered from Nov. 15 to Dec. 7, during which time omicron was first detected by scientists in South Africa and Botswana, and may change as time passes. Experts now say that omicron accounts for more than 90% of all new infections in South Africa, according to Discovery Health chief executive Dr. Ryan Noach.

The country is experiencing rapid spread of the virus — concentrated in its most populous province, Gauteng. The seven-day rolling average of daily new cases in South Africa has risen during the past two weeks from 8.07 new cases per 100,000 people on Nov. 29 to 34.37 new cases per 100,000 people on Monday, according to Johns Hopkins University. The death rate hasn’t increased during that same period.

“The omicron-driven fourth wave has a significantly steeper trajectory of new infections relative to prior waves. National data show an exponential increase in both new infections and test positivity rates during the first three weeks of this wave, indicating a highly transmissible variant with rapid community spread of infection,” Noach said.

Although cases are rising, hospitalizations are not increasing at the same rate, leading the scientists to report that the risk of hospitalization from omicron is lower than delta or earlier variants. Hospital admissions for adults diagnosed with COVID-19 are 29% lower compared to the wave that South Africa experienced in mid-2020, after adjusting for vaccination status, according to the analysis.

The U.K. Health Security Agency said Friday that new data from the U.K. confirm that omicron is more easily transmissible than other variants. Other studies suggest that both the AstraZeneca and Pfizer vaccines are less effective in preventing symptomatic infections in people exposed to omicron, though preliminary data show that effectiveness appears to rise to between 70% and 75% after a third booster dose.

The study also found that omicron poses a higher risk of reinfection. For individuals who have previously had COVID-19, the risk of reinfection with omicron is significantly higher than that of earlier variants.

Pfizer’s COVID-19 pill appears effective against omicron

Pfizer said Tuesday that its experimental COVID-19 pill appears effective against the omicron variant, the Associated Press reported.

The company also said full results of its 2,250-person study confirmed the pill’s promising early results against the virus: The drug reduced combined hospitalizations and deaths by about 89% among high-risk adults when taken shortly after initial COVID-19 symptoms.

Separate laboratory testing shows the drug retains its potency against the omicron variant, the company announced, as many experts had predicted. Pfizer tested the antiviral drug against a human-made version of a key protein that omicron uses to reproduce itself.

The updates come as COVID-19 cases, deaths and hospitalization are rising again and as the U.S. hovers around 800,000 pandemic deaths. The latest surge, driven by the delta variant, is accelerating due to colder weather and more indoor gatherings, even as health officials brace for the impact of the emerging omicron mutant.

The Food and Drug Administration is expected to soon rule on whether to authorize Pfizer’s pill and a competing pill from Merck, which was submitted to regulators several weeks earlier. If granted, the pills would be the first COVID-19 treatments that Americans could pickup at a pharmacy and take at home.

What we know about the previous North Texas omicron cases

The North Texas omicron cases from last week involve a 35-year-old man from Tarrant County and a 40-year-old man from Collin County, Ayass Bioscience said. The 40-year-old patient, who lives in Plano, reported mild symptoms, while the 35-year-old patient, who knew he had been exposed to the virus, reported no symptoms.

Both men received the Pfizer vaccine, but neither got a booster dose, said Dr. Mohamad Ayass, president and founder of Ayass Bioscience. Neither patient has a recent travel history.

Collin County Health Care Services confirmed Thursday that the 40-year-old patient tested positive for the new strain.

“At this time, it is the only lab-confirmed case of the omicron variant in Collin County,” said Darrell Willis, public information officer for the country’s health care services department.

A Tarrant County Public Health official said the department is in the process of reviewing the case of the 35-year-old man.

What patient travel history tells us about community spread

Neither the two North Texas omicron cases nor the first case of the variant identified in Harris County had any recent travel history, meaning the patients likely contracted the virus locally.

“It’s pretty clear that there’s been evidence of community transmission going on in the state and likely in North Texas,” Cutrell said.

Houston has also detected the omicron variant in eight of its wastewater treatment facilities, city health department officials said last week. The plants where the variant was identified aren’t concentrated in one area.

“That tells us, more than likely, that the variant is here, circulating in the community already,” said Scott Packard, chief communications and public affairs officer at the Houston Health Department.

What you can do to protect yourself against omicron

The best line of defense against the variant, Cutrell of UT Southwestern said, is to get the COVID-19 vaccine.

Pfizer said last week that a booster dose of its vaccine may protect against omicron even though the initial two doses appear less effective. The Pfizer booster dose is available to anyone ages 16 and older who received the first two doses of the vaccine at least six months ago.

“We’re in the midst of the holiday season, and people are traveling more, getting together with family and gathering. We really want to encourage people to get fully vaccinated and get their booster before they start doing all that traveling and gathering,” Cutrell said. “But, also, make good decisions about using masks and getting tested before you go to a large gathering.”

The Associated Press contributed to this report.