The 1st US Clade I Mpox Case Has Been Found in the Bay Area. Here’s What to Know

Health officials confirmed this weekend that the first U.S. case of a new mpox strain had been detected in the Bay Area.

This variant of mpox — formerly called monkeypox — is known as clade I and has been circulating in eastern and central Africa over the last year, where it’s caused sickness among children and adults and even deaths. The disease usually spreads through close skin-to-skin contact, including sex.

The Centers for Disease Control and Prevention (CDC) announced Saturday that the U.S.’s first known clade I case had recently returned from travel to the African continent and was treated for mpox symptoms at a medical facility in San Mateo County.

Clade I is a more severe strain of mpox compared to the clade II strain that caused an outbreak in the Bay Area in 2022 and that is still circulating at low levels. But the CDC has said that the risk of clade I mpox to the general public within the U.S. “remains low.” A two-dose vaccine for mpox, which offers protection against both clade I and clade II, remains available for eligible people at higher risk of infection.

Jump straight to:

• Who’s eligible for an mpox vaccine in the Bay Area?
• Who is most at risk from mpox?

Keep reading for what we know about this new U.S. case of clade I mpox, how mpox spreads, what symptoms to be aware of and who should get an mpox vaccine.

What do we know about this first clade I mpox case in the U.S.?

Not a great deal — because health officials don’t want to release details that could identify this person.

We know that the patient received medical care at a facility in San Mateo County and had recently returned from travel to Eastern Africa. The patient is now isolating at home, the CDC said — although their home county hasn’t been disclosed — and their symptoms are improving. “It has not been a severe illness” for this patient, San Mateo County health officer Dr. Kismet Baldwin-Santana said.

“People who had close contact with this individual are being contacted by public health workers, but there is no concern or evidence that mpox clade I is currently spreading between individuals in California or the United States,” the California Department of Public Health (CDPH) said in a statement.

Baldwin-Santana said that officials were also “actively working” with San Mateo health care staff “that have been exposed.”

Dr. Peter Chin-Hong, an infectious disease expert at UCSF, said that the first U.S. case of clade I was “expected,” owing to the scale not just of the outbreak in eastern and central Africa but of international travel. “It was only a matter of time before we saw cases in the U.S. from people who traveled there,” he said.

What is clade I mpox, and where is it spreading?

The mpox virus spreads through close contact with someone who is infected and causes mpox disease. As the name might suggest, the virus is related to the smallpox virus, but it’s generally less severe and much less contagious than smallpox, according to CDPH. In addition to fever, chills, headache and muscle pain, mpox can cause a painful rash — also known as lesions — that appear on many parts of the body.

In August, the World Health Organization (WHO) declared a clade I mpox outbreak in eastern and central Africa a global emergency. Historically, this strain has caused more severe illness and higher fatality rates than the other type of mpox, clade II.

The Democratic Republic of the Congo (DRC), which has been the epicenter of the outbreak, has reported more than 9,000 confirmed clade I mpox cases and more than 40 deaths since Jan. 1. Clade I mpox has also spread to Burundi, Central African Republic, Republic of the Congo, Rwanda and Uganda. Very few doses of the mpox vaccine were originally available on the African continent, but in October, 265,000 doses arrived in the DRC for distribution among vulnerable groups.

In August, the first clade I mpox case outside the African continent was detected in Sweden. Subsequent cases of people who had recently traveled to affected regions in Africa have also been detected in Germany, India, Kenya, Thailand, the United Kingdom, Zambia and Zimbabwe — and now the U.S.

How is clade I different from the type of mpox that hit the Bay Area in 2022?

The 2022 mpox outbreak in the United States — which particularly affected gay and bisexual men, as well as trans and nonbinary people who have sex with men — was caused by clade II mpox, the less severe strain. Read more about the 2022 outbreak.

2024’s clade I mpox is also different because it’s “not really in a sexual network per se,” UCSF’s Chin-Hong said — that is, groups of people who are connected to one another sexually. In 2022, clade II “was engineered, almost, to be very efficiently spread within a sexual network, and it was amplified by a lot of things happening at the same time, like Pride events.”

The clade I strain that’s been spreading in eastern and central Africa “primarily affects heterosexual people and children within households,” Chin-Hong said — but with the caveat that this exposure within a home has to be “intensive.”

Data from Stanford University’s WastewaterSCAN project, which monitors the presence of viruses, including mpox, in human sewage across the U.S., shows that more than two years after the initial 2022 outbreak, clade II of mpox is still occasionally detected in the Bay Area’s wastewater.

Dr. Julia Janssen, deputy director of the HIV/STI Prevention and Control Branch at the San Francisco Department of Public Health, stressed that the city had seen 31 confirmed cases this year — and that Bay Area residents at higher risk of infection should still stay vigilant for clade II mpox by getting their mpox vaccine.

Who is at higher risk of getting clade I mpox?

“Nothing has led us to believe up till now that there is a heightened risk to the general public” from clade I mpox, San Mateo County’s Baldwin-Santana said, echoing the CDC and CDPH. “Most people in the public really should not be too concerned at this point in time.”

The CDC said that the large number of children getting clade I in eastern and central Africa likely shows that it’s spreading within households and between family members. “Based on what we know right now, we don’t expect to see the same sort of risk if mpox were introduced in the United States for several reasons, including different household makeup and size, access to disinfecting products and improved access to medical care,” the agency said.

Based on its own models, the CDC also said that close-contact transmission within and between households “is unlikely to result in a large number of mpox clade I cases” nationally.

Clade I is “nothing to worry about for the general population” in the Bay Area, UCSF’s Chin-Hong said. “It’s still very hard to get mpox, even from somebody with active lesions. It requires close skin-to-skin contact or intensive household contact — so you can’t get it from Muni or from yoga or from going to Trader Joe’s.”

Clade II mpox remains a much more real threat in the Bay Area right now than this one clade I case, Chin-Hong said, since that strain is still circulating at low levels in the region. It’s “a great reminder for people to continue to pay attention to that — that is, people in the LGBTQ community — to really make sure they’re up to date on vaccines,” he said, reminding folks that gay and bisexual men and other men who have sex with men, as well as transgender, nonbinary and gender-diverse people, are at greater risk for a clade II infection. Jump to where to find an mpox vaccine. 

What are the symptoms of mpox, and how does it spread?

The mpox virus spreads through close — usually skin-to-skin — contact with someone who is infected. This could be direct contact with the infectious rashes or scabs someone with mpox develops, scabs, having intimate physical contact with someone who has mpox, such as kissing, cuddling or sex. Coming into contact with infected bodily fluids or items that have been touched by rashes or fluids from an infected person can also expose you to the virus.

The symptoms of clade I and clade II mpox are similar, SFDPH’s Janssen said, and they can often start as flu-like conditions — which is worth bearing in mind as the Bay Area enters respiratory virus season.

The mpox virus also appears as a rash or sores or spots that can resemble pimples or blisters on the skin anywhere on the body, including the face, inside the mouth, hands, feet, chest, genitals and anus. These spots often start as red, flat spots that then become bumps before the bumps become filled with pus and turn into scabs when they break. These symptoms can be extremely painful. If you’re unsure about recognizing an mpox rash, the CDC has a photo guide.

Mpox can have a long incubation period — that is, the time between when you’re exposed to mpox and when you start to develop symptoms — that can range from three to 17 days, according to the CDC.

If you suspect you might have mpox symptoms — even if they’re subtle — see your health care provider right away or consult one of SFPDH’s clinics for mpox testing. See more on what to do if you suspect you have mpox.

Who’s eligible for an mpox vaccine in the Bay Area?

The vaccine currently available in the U.S. (brand name: Jynneos) is a two-dose series, with roughly a month between doses. Maximal immunity will build two weeks after your second dose. If you only got one dose previously, go ahead and seek out your second dose ASAP.

The U.S. Department of Health and Human Services said in a statement that people who have received both doses of the mpox vaccine — along with people who have already had clade II mpox — “are expected to be protected against severe illness from clade I mpox” as well.

The CDC recommends the two-dose mpox vaccine to gay and bisexual men and other men who have sex with men, as well as transgender, nonbinary or gender-diverse people who in the past 6 months, have had:

• More than one sexual partner and/or
• A new diagnosis of one or more sexually transmitted infections.

The CDC’s vaccine recommendations also include anyone who has had sex at a commercial sex venue like a sex club or bathhouse. See the full mpox vaccine eligibility recommendations from the CDC.

San Francisco additionally recommends vaccination for anyone living with HIV, anyone taking PrEP or who’s eligible to take it and sex workers.

The CDC has recently updated its vaccination recommendations to extend to people traveling to countries with clade I outbreaks, which as of Nov. 16 include Burundi, Central African Republic, Democratic Republic of the Congo, Republic of the Congo, Rwanda and Uganda. The agency recommends getting both doses of the vaccine “if you anticipate experiencing any of the following” while traveling to these countries:

• Sex with a new partner
• Sex at a commercial sex venue, such as a sex club or bathhouse
• Sex in exchange for money, goods, drugs or other trade
• Sex in association with a large public event, such as a rave, party or festival.

The mpox vaccine was also originally only available for people aged 18 and older, but in 2022 the Food and Drug Administration (FDA) issued an emergency-use authorization that allows providers to also give the vaccine to young people under 18 who are “determined to be at high risk” of infection.

Where can I find an mpox vaccine?

If you have a regular health care provider, SFDPH recommends you ask them first about getting the mpox vaccine. Your vaccine will be free, but you may be charged a regular copay for seeing your provider.

If you’re eligible for the vaccine, your health insurance should cover the costs thanks to the CDC’s recommendations. If you don’t have a regular health care provider or insurance, you can find the mpox vaccine free at clinics around the Bay Area. You can opt to schedule an appointment or choose a walk-in clinic, depending on what works best for you.

(As with the COVID-19 vaccine, receiving an mpox vaccine won’t make you a public charge or affect any future immigration processes you may enter into, and you won’t be asked about your immigration status to receive the mpox vaccine.)

If you live in or near San Francisco:

See a full list of mpox vaccine sites near you in San Francisco. SFDPH confirms that you don’t have to be a city resident in San Francisco to get vaccinated for mpox.

Mpox vaccination sites elsewhere in the Bay Area and California:

• Find an mpox vaccine clinic near you using the CDC’s Vaccine Locator
• Find an mpox vaccine clinic near you using the state’s myturn.ca.gov site

Getting an mpox vaccine at a pharmacy

Some pharmacies offer mpox vaccination appointments online, along with other vaccines like COVID-19 and flu. But if you choose this route, you’ll be asked for insurance details — and it’s important to verify with your insurer ahead of time that they’ll cover the cost of an mpox vaccine at a pharmacy like CVS or Walgreens, as the out-of-pocket costs you’ll be quoted may be steep. If you find your insurance doesn’t fully cover the cost, SFDPH said you can seek your vaccine at one of their clinics while supplies last.

If you get your health care through a health system like Kaiser Permanente, it’s unlikely you’ll be able to get your mpox vaccine covered by insurance at a pharmacy like CVS or Walgreens — the way you can’t get your COVID-19 or flu shot covered by Kaiser at a pharmacy either — and may have to seek it directly from a Kaiser provider.

If you’re able to make an appointment online at a pharmacy for your mpox vaccine, you should consider calling that location ahead of time to verify that they do indeed have supply in stock.

This story includes reporting from KQED’s Billy Cruz, Carlos Cabrera-Lomelí and Nisa Khan.