More than two months after the first case was detected in the United States, an outbreak of monkeypox virus is continuing to spread quickly nationwide and in the Bay Area, mostly among gay and bisexual men, and is showing no signs of slowing down.
New cases could continue to rise at a faster pace for weeks, if not longer, and eradicating the disease altogether may prove difficult, infectious disease experts and local health officials say, though the exact trajectory is hard to predict. How quickly high-risk people can get vaccinated in large numbers — as well as how much behavioral changes can mitigate transmission in communities where it’s spreading the most — will shape how well and how fast the outbreak can be wrested under control.
A limited supply of monkeypox vaccine has fueled concerns that the disease could spread further into the LGBTQ community and into the wider population, though that hasn’t happened yet.
“Judging by the curve of the outbreak, we’re definitely on the increasing phase,” said Dr. Bela Matyas, public health officer for Solano County. “I anticipate we’ll continue to see this will rise for a while longer because I don’t see evidence of cresting yet.”
Eventually, he said, “It’ll crest and start to come back down. The real question is: Will it remain endemic in this community because we can’t get rid of it? Or will we be able to successfully get rid of it?”
In San Francisco, the jurisdiction with the second-highest number of infections in California after Los Angeles County, cases are roughly doubling each week — prompting the city Thursday to declare monkeypox a local state of emergency. As of Wednesday, the most recent day for which there is data, there were 281 confirmed and probable cases in San Francisco — up from 141 just over a week ago and 60 a week before that, according to the city Department of Public Health. The US epidemic curve is similarly rising, reaching about 4,900 cases to date.
Monkeypox in the Bay Area
“We’re still in a phase of increasing spread,” said Dr. Stephanie Cohen, medical director of San Francisco City Clinic, who is helping manage the public health department’s monkeypox response.
Monkeypox, a less severe cousin of smallpox, is an old virus that has been endemic in West Africa for years. The current outbreak is worrisome because it’s circulating in large numbers in parts of the world that don’t typically see many infections.
For a public collectively traumatized by SARS-CoV-2 — a virus that caused deadly disease before it was tamed by vaccines — the spread of monkeypox may sound scary. But experts say there are key differences that may be reassuring: The version causing the current epidemic is less severe than the one circulating in West Africa. Among the thousands of cases in the US, no one has died, and the vast majority of patients don’t need hospitalization, although the lesions caused by the virus can be uncomfortable and even debilitating if they’re on or near the eyes, mouth , urethra or rectum because they make daily activities painful.
Monkeypox is a DNA virus, not an RNA virus like the virus that causes COVID-19, which means it’s more stable and likely won’t mutate quickly the way COVID has. Unlike COVID, monkeypox is largely spread through prolonged skin-to-skin contact, such as sexual contact—not from sharing air space for short periods of time. This dramatically alters its path to proliferation.
Locally and nationally, monkeypox has so far largely been contained to gay and bisexual men who transmitted the virus through intimate contact — often, health officials believe, as a result of multiple sexual encounters, including with anonymous partners. Monkeypox is not a sexually transmitted infection in and of itself, but physical encounters allow for the necessary sustained contact for transmission.
About 98% of cases in San Francisco are in males and the remaining 2% are trans male, and nearly 90% are gay, lesbian or same-gender loving, according to the city’s most recent demographic data.
There has been some but not major spillover recently to the broader population beyond gay and bisexual men — two cases among US children were reported late last week by the CDC. But the children likely got it from household contact with a known case, since it can also be spread by touching the same sheets or clothing, or by nonsexual skin-to-skin encounters such as holding a child or sleeping in the same bed.
The fact that the children did not get it from an unknown source — which would have indicated more widespread community transmission — is reassuring, said Dr. Abraar Karan, a Stanford infectious disease physician. The highest risk remains within sexual networks, which is why researchers are also keeping an eye on other high-risk groups such as female sex workers and people with many partners who seek frequent treatment at sexual health clinics.
“We haven’t seen significant spillover yet, outside men who have sex with men,” Karan said. “The fact that this hasn’t spilled over more at this point suggests you need prolonged intimate contact the way you’d see in sexual networks.”
There are now so many monkeypox cases around the world, there’s a high chance the virus has also entered reservoirs of animals such as rodents — which means there could be ongoing transmission from them back to humans, Karan said.
“Eradication will be tough,” he said. “For at least the foreseeable future, we’ll have at minimum a low level of cases in the community once we get this initial outbreak under control. Eliminating this further is going to be very tough.”
Federal health officials said Thursday they’ll be making an additional 780,000 doses of the Jynneos monkeypox vaccine available Friday. But that’s expected to fall well short of the current need. San Francisco requested 35,000 doses for its high-risk residents and so far has only received several weekly batches of a few thousand doses each. The city’s main public vaccine clinic had to close to walk-ins this week after running out of supply, and vaccine providers have had to shift to a one-dose strategy to give more people partial protection. The shot is supposed to be given in two doses, at least four weeks apart, and the one-dose strategy means people who’ve gotten their first dose will probably not be able to get their second until global vaccine supply improves.
“If we had infinite amounts of vaccine, which we don’t, how quickly could we get this under control? I’d like to think we could get it under control fairly quickly,” said Dr. Art Reingold, a professor of epidemiology at UC Berkeley’s School of Public Health. “But we don’t have unlimited quantities of vaccine and won’t for quite some time. I think we will continue to see transmission at least in the coming weeks. There’s just infected people out there. And they have contact with other people.”
Catherine Ho (she/her) is a San Francisco Chronicle staff writer. Email: cho@sfchronicle.com Twitter: @Cat_Ho