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As California health officials investigate an outbreak of a more severe type of mpox virus, federal data indicate that across the country most of the people at highest risk of exposure haven’t been vaccinated against the disease.
In most states – including Georgia, Florida, Texas, Michigan, and New Jersey – more than half of at-risk people remained unvaccinated in the wake of the 2022-23 U.S. outbreak of a milder form of the virus that infected more than 30,000 people, according to Centers for Disease Control and Prevention estimates last updated in January 2024.
Mpox, which causes a rash and sores that can be painful, is spread mostly through close, intimate, and sexual contact.
Fewer than one-quarter of at-risk people in most states were fully vaccinated with two doses of the mpox vaccine, the CDC data show. Even in the jurisdictions with the highest levels of people fully vaccinated against mpox – the District of Columbia, at 68%, New York City, at 47%, and California at 43% – many at-risk people were not fully vaccinated.
It’s likely that mpox immunization rates are even lower today, as the earlier mpox outbreak has faded from the headlines and is “out of sight, out of mind,” said Dr. Peter Chin-Hong, an infectious disease specialist at the University of California, San Francisco.
“It’s a wake-up call for at-risk populations to be up-to-date on their vaccines, because a lot of people are not,” Chin-Hong said. “They might have gotten the first shot back in 2022 when everyone was afraid, and people knew a lot of people who had it.”
None of the three Southern California residents hospitalized in the new outbreak were vaccinated against mpox, the California Department of Public Health said in an email to Healthbeat.
California cases of clade I are first in the U.S. without international travel
California public health officials last week began warning that a more virulent type of mpox that has primarily caused disease in African countries, called clade I, now appears to be spreading from person to person in their state.
The three California cases identified with clade I infections didn’t have any recent history of international travel, local, county and state health officials have said. They also didn’t have any connection to each other. Two lived in Los Angeles County, one in Long Beach. All are recovering from their infections, officials said.
They are the first reported clade I infections in the United States that don’t involve international travel, the California Department of Public Health said. These cases indicate that clade I is spreading in the community, “primarily impacting communities of gay and bisexual men, and other men who have sex with men, as well as their social networks,” the department said.
The clade I form of the virus can cause more severe disease than clade II type, which was involved in the 2022-23 outbreak. Vaccination and public health education campaigns caused a sharp drop in those clade II cases, but that form of the virus continues to circulate at low levels across the country.
Both forms of mpox, formerly called monkeypox, cause rashes that can initially look like pimples or blisters that may appear on the hands, face, mouth, chest, or near genitals. Mpox also can cause flu-like symptoms. The risk of severe disease is highest among people with weakened immune systems.
The two-dose mpox vaccine, called JYNNEOS, provides protection against both clade I and clade II mpox, health officials said. For those who have already received two doses, a third booster shot is not recommended.
At-risk people encouraged to get mpox vaccine
While California health officials said the risk to the public is low, they are encouraging people at increased risk of mpox exposure to get vaccinated, including people who are gay, bisexual, and men who have sex with men, transgender, and non-binary people, and people who have been exposed to someone with mpox.
The virus primarily spreads through close contact with an infected person, such as through intimate physical contact during massages, cuddling, or sex, or sharing a living space or personal items with someone who has mpox. Casual contact, such as interactions in an airplane, office, or store, are unlikely to spread the virus, California’s state health department said.
There is no indication so far that the clade I outbreak in California is spreading to other states.
“We have to be vigilant, but not scared,” Chin-Hong said. “If it gets into the right place at the right time, like what happened in 2022, it could potentially take off again.”
While California has only identified three cases of clade I mpox, Chin-Hong said there are probably more people who haven’t sought treatment or been diagnosed, despite painful sores and other symptoms that can take three weeks to run their course.
Chin-Hong said he found it interesting that all three of the identified cases were hospitalized.
“Either it’s something about clade I, or it could be that the people who were identified happened to have more serious cases,” he said, “and people who had milder cases just didn’t bother to come to see anybody about it.”
The mpox vaccine is available across the United States through a mix of public health departments, community clinics, and retail pharmacies, said Mark Clarke, a spokesperson for Bavarian Nordic, which makes the JYNNEOS vaccine.
The vaccine, which is given as two injections four weeks apart, is generally covered by health insurance, Clarke said, and those without coverage may find free or reduced-cost vaccine from local health departments and LGBTQ+ focused clinics. The company’s locator tool www.EmpoweredAgainstMpox.com – provides locations that may offer the vaccine.
Spokespeople for CVS and Walgreens told Healthbeat that in most cases, people seeking mpox vaccination will need to make an advance appointment because it can take a few days to ship the vaccine to their local pharmacy.
Chin-Hong said the emergence of what appear to be locally spread clade I cases in California illustrate the broader importance of public health activities in the United States and around the world.
By the United States helping other countries combat infectious diseases, he said, it helps protect against the spread of diseases spreading here.
“We need to continue to invest in public health. That’s what keeps us safe,” he said. He noted that the California cases have been identified as clade I in the middle of a federal shutdown that has impacted the CDC. “You need to invest in people and surveillance, diagnostics and prevention with vaccines to keep everyone safe.”
The CDC has been doing genomic testing to learn more about the virus that infected each of the clade I cases in California, the Los Angeles County Department of Public Health has said.
The CDC did not respond to questions from Healthbeat about mpox vaccination rates across the country and the potential for clade I spreading beyond California. A spokesperson for the U.S. Department of Health and Human Services told Healthbeat to seek information about the new California outbreak from state health officials and the CDC webpage about the disease.
When asked about the impact of the federal shutdown on the mpox outbreak response, the California Department of Public Health told Healthbeat by email that the department continues to work with available staff at CDC, “but the recent federal government shutdown and other actions at the federal level have added a layer of uncertainty to the current work environment.”
Alison Young is Healthbeat’s senior national reporter. You can reach her atayoung@healthbeat.orgor through the messaging appSignalat alisonyoungreports.48
