The omicron variant of the coronavirus has arrived in Texas, Harris County Judge Lina Hidalgo said in a tweet on Monday night. A 40-year-old woman in Harris County with no recent travel history tested positive for the variant, Hidalgo said.

The woman is fully vaccinated and experienced COVID-19 symptoms, according to the Harris County Public Health Department. She has not required hospitalization.

“The fact that the patient did not have a travel history means she picked it up in the community. So it’s here, it has been here probably for a week or two,” said Catherine Troisi, associate professor of epidemiology at the University of Texas Health Science Center at Houston.

Genetic sequencing tests this week showed that the woman’s recent COVID-19 case was the omicron variant, the Texas Department of State Health Services confirmed.

Dr. John Hellerstedt, a DSHS commissioner, said the variant’s arrival in Texas was unsurprising. “It’s normal for viruses to mutate, and given how quickly omicron spread in southern Africa, we’re not surprised that it showed up here,” Hellerstedt said.

“Getting vaccinated and continuing to use prevention strategies, including wearing a mask when you are around people you don’t live with, social distancing, handwashing and getting tested when you have symptoms, will help slow the spread of the virus and help end the pandemic,” he said.

Texas Gov. Greg Abbott and his aides did not immediately respond to a request for comment Monday. The Republican governor has refused so far to mandate any protective measures against COVID-19 and has forbidden state or local government entities from imposing their own mandates.

As of Monday, almost 65% of the Texas population has received at least one dose of a COVID-19 vaccine and 55% have been fully vaccinated, according to the U.S. Centers for Disease Control and Prevention. That is well below the national average of 71% receiving at least one dose and 60% being fully vaccinated.

Troisi said there’s no reason to panic. “We need to protect ourselves, and we have ways of doing that,” she said. She expects other large Texas cities will see their own cases soon, although the variant will likely take longer to spread to rural communities.

Dr. Philip Huang, director and health authority for Dallas County Health and Human Services, encouraged residents to get vaccinated and to receive their COVID-19 booster shots. He said residents should continue following coronavirus-related precautions, including social distancing, washing hands and wearing face coverings.

Huang urged people to consider family members who are at high risk for severe symptoms of COVID-19 before traveling for the holidays. “We continue to work with the state to monitor for omicron and we also continue to get vaccinations out to the community and promote prevention messages to do everything we can to try to slow the spread of the virus,” he said.

The omicron variant, first detected in South Africa, appears to have more than 30 mutations in the coronavirus’ spike protein, which could affect how easily it spreads to people.

Last Wednesday, the White House announced that a person in California who had been vaccinated against COVID-19 became the first in the U.S. to have an identified case of the omicron variant. Scientists continue to study the risks posed by the new virus strain. As of Monday, omicron has been detected in 19 U.S. states, including New York, Minnesota, Colorado, Hawaii, Nebraska, Pennsylvania and Maryland.

Dr. Anthony Fauci, President Joe Biden’s chief medical adviser, told reporters that the person in California was a traveler who returned from South Africa on Nov. 22 and tested positive Nov. 29. Fauci said the person had been vaccinated but had not received a booster shot and was experiencing “mild symptoms.”

It’s still unclear whether the genetic changes in the new variant will pose a public health threat. Some previous variants, like the beta variant, initially alarmed scientists but didn’t end up spreading very far.

Fauci told Biden it would take about two more weeks before there was more information on the transmissibility, severity and other characteristics of the variant, but said he believed vaccines would continue to provide a degree of protection, The Washington Post reported.

Since being first detected, the variant has appeared in virus samples around the world. Cases have been identified in more than 40 countries, including Australia, Botswana, Britain, Belgium, Botswana, the Czech Republic, Denmark, Germany, Hong Kong, Israel, Italy and the Netherlands, according to The Washington Post, The New York Times and the Associated Press.

Cecilia Tomori, director of global public health and community health at the Johns Hopkins University School of Nursing, said Americans should first be worried about the continued spread of the delta variant. Delta has become the dominant variant in the U.S., accounting for more than 99% of all new cases, according to the Centers for Disease Control and Prevention.

“We are not adequately concerned by how bad our current surge is,” Tomori said. “We haven’t been adequately concerned about where we’ve been, which is a very high case number per day and a very high number of hospitalizations and deaths for a very, very long time.”

She said she hopes concern over the omicron variant will push people to use strategies to prevent coronavirus transmission, like getting vaccinated.

What are Biden’s winter plans to respond to the new omicron variant?

Biden kicked off a more urgent campaign for Americans to get COVID-19 booster shots Thursday as he unveiled his winter plans for combating the coronavirus and its omicron variant with enhanced availability of shots and vaccines but without major new restrictions, the AP reported.

The plan includes requiring private insurers to cover the cost of at-home COVID-19 tests and tightening testing requirements for people entering the U.S. regardless of their vaccination status. But as some other nations close their borders or reimpose lockdowns, officials said Biden was not moving to impose additional restrictions beyond his recommendation that Americans wear masks indoors in public settings, the AP reported.

As of Monday, all travelers to the U.S., regardless of nationality or vaccination status, will need to provide proof of a negative COVID-19 test within one day of boarding their flights. That’s down from three days right now for those who have been vaccinated, in an added precaution against the omicron variant. But the White House has shelved tougher options, like requiring post-arrival testing or requiring quarantines upon arrival in the U.S., the AP reported.

Where has the omicron variant been detected?

The New York Times reports that, in the U.S., omicron has been detected in California, Colorado, Connecticut, Georgia, Hawaii, Louisiana, Maryland, Massachusetts, Minnesota, Mississippi, Missouri, Nebraska, New Jersey, New York, Pennsylvania, Texas, Utah, Washington and Wisconsin, according to reporting by The New York Times, The Washington Post and the Associated Press.

The variant has been detected in South Africa, Botswana, Zambia and Zimbabwe, as well as in travelers to Austria, Brazil, the Czech Republic, Finland, France, Ghana, Greece, Hong Kong, Ireland, Italy, Japan, Luxembourg, Malaysia, Mexico, the Netherlands, Nigeria, Norway, Reunion, Saudi Arabia, Singapore, South Korea, Sri Lanka, Sweden, Switzerland, Tunisia and the United Arab Emirates, according to The New York Times. Omicron cases have also been reported in Australia, Belgium, Britain, Canada, Denmark, Germany, Iceland, India, Israel, Norway, Portugal and Spain.

Why are scientists worried about the omicron variant?

The omicron variant appears to have more than 30 mutations in the coronavirus’ spike protein, which could affect how easily it spreads to people, the Associated Press reported.

Sharon Peacock, who has led genetic sequencing of COVID-19 in Britain at the University of Cambridge, said the data so far suggest the new variant has mutations “consistent with enhanced transmissibility,” but said that “the significance of many of the mutations is still not known.”

Even though some of the genetic changes in the new variant appear worrying, it’s still unclear whether they will pose a public health threat. Some previous variants, like the beta variant, initially alarmed scientists but didn’t end up spreading very far.

What do scientists know about the omicron variant?

The variant was identified last week by researchers in South Africa. Much is still not known about it, including whether it is more contagious, more likely to cause serious illness or more able to evade the protection of vaccines, the Associated Press reported.

On Friday, scientists in South Africa said that omicron appears to spread more than twice as quickly as delta, which had been considered the most contagious version of the virus, The New York Times reported. Omicron’s rapid spread results from a combination of contagiousness and an ability to evade the body’s immune defenses, the researchers said, but the contribution of each factor is not yet certain. The research has not been appeared in a scientific journal or been peer-reviewed.

Fauci told Biden it would take about two more weeks before there was more information on the transmissibility, severity and other characteristics of the variant, but said he believed vaccines would continue to provide a degree of protection, The Washington Post reported.

Dr. Francis Collins, director of the National Institutes of Health, said that there is no data yet that suggests the new variant causes more serious illness than previous COVID-19 variants, the AP reported.

“I do think it’s more contagious when you look at how rapidly it spread through multiple districts in South Africa. It has the earmarks, therefore, of being particularly likely to spread from one person to another... What we don’t know is whether it can compete with” the delta variant, Collins said recently on CNN’s “State of the Union.”

Collins said everyone should redouble their efforts to use the tools the world already has, including vaccinations, booster shots and measures such as mask-wearing, the AP reported.

Collins said that vaccination remains the first line of defense, saying that there are “good reasons” to believe, based on previous variants, that current vaccines will provide sufficient protection, The New York Times reported.

“Please, Americans, if you’re one of those folks who’s sort of waiting to see, this would be a great time to sign up, get your booster,” Collins said recently on Fox. “Or if you haven’t been vaccinated already, get started.”

While some experts say that early signs indicate that the omicron variant may cause only mild illness, it’s too early to assume that the variant will not cause severe illness, too, Dr. Richard Lessells, an infectious diseases specialist in South Africa, told The New York Times. Many of the early infections in South Africa were identified among younger people more likely to experience mild illness, he said.

What travel restrictions have been put in place because of the omicron variant?

CNN is maintaining a list of travel restrictions by country during the omicron variant outbreak, although it cautions that governments can change their regulations at a moment’s notice.

The European Union is restricting travel to and from seven countries in southern Africa — Botswana, Eswatini, Lesotho, Mozambique, Namibia, South Africa and Zimbabwe — while the U.S. and South Korea have targeted those countries and Malawi, according to The New York Times. Britain has restricted travel with those eight nations and Angola and Zambia. Israel announced it was sealing its borders to all foreigners for 14 days after one case was confirmed in the country.

Many countries are introducing such bans, though they go against the advice of the World Health Organization, which has warned against any overreaction before the variant is thoroughly studied, the AP reported.

South Africa’s government responded angrily to the travel bans, which it said are “akin to punishing South Africa for its advanced genomic sequencing and the ability to detect new variants quicker.” It said it will try to persuade countries that imposed them to reconsider, the AP reported.

What do variants like omicron reveal about global vaccine inequities?

Some experts said the variant’s emergence illustrated how rich countries’ hoarding of vaccines threatens to prolong the pandemic, the AP reported.

Fewer than 6% of people in Africa have been fully immunized against COVID-19, and millions of health workers and vulnerable populations have yet to receive a single dose, the AP reported. Those conditions can speed up spread of the virus, offering more opportunities for it to evolve into a dangerous variant.

“This is one of the consequences of the inequity in vaccine rollouts and why the grabbing of surplus vaccines by richer countries will inevitably rebound on us all at some point,” said Michael Head, a senior research fellow in global health at Britain’s University of Southampton.

The Associated Press contributed to this report.