Officials confirmed Wednesday that the first U.S. case of COVID-19 caused by the worrisome omicron variant was confirmed in a San Francisco resident who had recently traveled to South Africa.

Here’s what you need to know:

Q: How was the case discovered?

A: The person is a San Francisco resident who returned to the city from South Africa on Nov. 22. The person felt symptoms of COVID-19, was tested for the virus on Nov. 29 and self-isolated at home. The positive test was confirmed as the omicron variant early Wednesday morning.

Q: Was the traveler vaccinated?

A: Yes. The person was been fully vaccinated with the Moderna vaccine, but did not yet fall within the six-month window for a recommended booster shot.

Q: What else do we know about the traveler?

A: Authorities would not reveal the patient’s age or gender, citing a need to protect privacy.

Q: How sick is the person?

A: San Francisco health officials said the patient is experiencing mild symptoms and appears to be recovering.

Q: If the San Francisco patient was fully vaccinated and not due for a booster, does that mean the vaccines don’t work on omicron?

A: No. While there is concern that omicron may be more vaccine-resistant based on the unusual number of mutations it carries, health officials say it’s too early to tell for sure. More broadly, experts still believe vaccines are the best defense against the virus and encourage everyone to get vaccinated or get a booster shot if they’re due, and wear face masks in indoor public settings. State Health and Human Services Secretary Dr. Mark Ghaly said Wednesday that the San Francisco patient’s mild symptoms demonstrate the value of the vaccines.

Q: Why is this variant so concerning?

A: The World Health Organization named omicron a variant of concern Friday after South African authorities reported a sharp increase in infections linked to it. In addition to their potential impact on vaccine effectiveness, the mutations could affect how easily omicron spreads and the severity of illness it causes. None of those possibilities are yet known.

Q: Is it possible the patient spread omicron to others? What’s being done about that?

A: San Francisco health authorities said the patient has been isolating, and cooperating with outreach to close contacts, defined as people who had been within six feet of the person for 15 minutes or more during the period when the patient could be infectious. Those contacts have been told to get tested, but so far no additional cases have been identified.

Q: Didn’t the government restrict travel last week to keep this variant out of the country?

A: President Biden last Friday restricted travel to the U.S. by non-citizens from South Africa and seven other African countries, effective Monday. The San Francisco patient had returned from South Africa before then. Biden, who had criticized similar travel restrictions by former President Trump, said on Monday that his travel ban “can slow the speed of omicron” and that it “gives us time” to prepare and for more people to get vaccinated. Biden acknowledged the travel restrictions “cannot prevent” the virus from reaching the U.S. The restrictions also don’t apply to U.S. citizens and lawful residents.

Q: Are there other means in place to prevent infected people from coming to the U.S.?

A: International air travelers to the U.S. who aren’t citizens must provide proof of vaccination before boarding. Vaccinated U.S. citizens and lawful residents must show proof of vaccination and a negative COVID-19 test three days before their flight. If the traveler is unvaccinated, the test must be one day before the flight.