By Julie Steenhuysen
CHICAGO (Reuters) - Monkeypox cases in some large U.S. cities appear to be declining, matching trends seen in Europe, and experts are cautiously optimistic the outbreak may have peaked in places hit hardest hit by the virus.
The World Health Organization earlier on Thursday said monkeypox cases reported globally declined 21% last week, after a month-long trend of rising infections, but noted that U.S. cases continued to rise.
Nevertheless, some U.S. experts believe cases are starting to decline based largely on immunity from prior infection and behavior changes as awareness of the disease has grown. That does not mean the disease will be contained, they cautioned.
Since late May, the United States has recorded nearly 17,000 monkeypox cases. The outbreak, which so far has reached 80 countries outside of Africa, where the virus is endemic, is largely being transmitted among gay and bisexual men.
Monkeypox, which is spread through close contact with an infected individual and the pus-filled sores common to the disease, is rarely fatal.
Rollout of Bavarian Nordic's Jynneos vaccine has been slow because of low supplies of the shot, which is also approved to prevent smallpox. But heightened awareness of the risks and increased immunity appear to be slowing the spread.
"It's very likely that the epidemic peaked as of last week," said Dr. Gerardo Chowell, an infectious disease modeler at Georgia State University School of Public Health.
Chowell's latest model, released on Thursday, forecasts a continued slowdown in new infections in the United States over the next four weeks. The declines may not be enough to extinguish the outbreak, but should bring infections to "very low levels,” he said.
The U.S. Centers for Disease Control and Prevention (CDC) did not respond to requests for comment about the apparent trend.
Dr. Celine Gounder, an infectious disease epidemiologist and an editor-at-large at Kaiser Health News, said she believes behavior change is driving down monkeypox transmission, but cautioned that "people get fatigued by behavior change" and transmission may go up again.
"I suspect behavior change will stick only until folks get two doses of the Jynneos vaccine," she said.
For the moment, cases appear to be dropping in some large U.S. cities hardest hit by the outbreak.
New York City's health commissioner, Dr. Ashwin Vasan, in a tweet on Thursday acknowledged the declining cases. "We are cautiously optimistic about this data, but will be closely following to ensure it is a sustained trend."
Likewise, data tracking monkeypox infections in San Francisco and Chicago show cases starting to drop over the past few weeks.
Chicago Department of Public Health spokesman James Scalzitti said the city may be turning a corner but that more data is needed to confirm a downward trend.
There are other signs as well. According to data on the CDC's website, the percentage of positive tests in public health and some commercial labs - an indicator of transmission rates - has fallen sharply, from 55% positive on July 16 to 24% on Wednesday.
"I think there likely has been some bending of the curve," said Dr. Amesh Adalja, a senior scholar at Johns Hopkins Center for Health Security.
He too attributes the change to a combination of increased immunity, particularly among high-risk individuals who got infected early in the outbreak, behavior changes and increased awareness.
Howard Brown Health, a system of 10 federally-funded clinics in Chicago that has treated a third of Illinois' monkeypox cases, has seen decreases in both the number of cases and percentage of positive tests.
"I think that reflects a true decrease in incidence," said Laura Rusie, Howard Brown's director of epidemiology. "It's hard to say it's going to stick, but it's promising."