The virus formerly known as monkeypox hasn’t completely disappeared, but Colorado public health officials expect to only see sporadic cases here in 2023.
Mpox, which was renamed by the World Health Organization because of the racist discourse around it, took off in the United States in the summer of 2022 before infections rapidly dropped off. The virus, while first scientifically described in monkeys, is believed to circulate in rodents in parts of Africa, with spillovers to people.
At the peak in August, an average of more than 450 mpox cases were reported nationwide each day. By early January, there were only about four cases per day, according to the Centers for Disease Control and Prevention. The U.S. recorded 29,913 mpox cases in 2022 and 20 deaths.
In Colorado, mpox cases also peaked in August, with 157 recorded that month. In December, the Colorado Department of Public Health and Environment only reported 16 cases.
Milder cases of mpox may look like common sexually transmitted infections or even pimples, so it’s likely some people never knew they had it. Testing was also difficult to find when the virus was spreading more widely in early summer, so the state’s total may exceed the 403 official cases. There have been no mpox deaths confirmed in Colorado.
State epidemiologist Dr. Rachel Herlihy said the health department is making plans in case mpox starts to circulate more widely again, but she expects “sporadic” cases or small clusters this year. The infrastructure is still in place to trace people who were in close contact with someone who has mpox and to offer them vaccination, she said.
The vaccine is most effective before exposure, but can prevent or reduce symptoms if a person takes it in the days after encountering the virus. Mpox typically causes flu-like symptoms and a rash, and has a low fatality rate.
“In some ways, the mpox response has been a success,” she said.
Katheryn Jacobsen, an epidemiologist at the University of Richmond, said that the small number of cases would make it difficult for mpox to spread widely, at least in the near future. Furthermore, when few people are getting a virus, it doesn’t have many opportunities to mutate and become more contagious or better at evading the immune system, as the virus that causes COVID-19 has, she said.
“This is a pretty incredible thing,” she said.
Relatively difficult to spread
In Colorado, 95% of cases were in men and 85% of those who answered questions about their identities said they were gay or bisexual. The pattern was similar nationwide, and Black and Hispanic men were disproportionately affected both in Colorado and around the country.
Because the community of men who have sex with men is relatively small, the virus rapidly began to run out of people to infect as men either got the vaccine or recovered from an infection. Some women and heterosexual people got mpox, but it never became widespread in their networks.
It’s not clear how much of the credit for the drop in cases goes to vaccination, behavior changes or even the virus running out of susceptible people. At least at the height this summer, gay and bisexual men reported in surveys that they had reduced their number of partners, and more than 600,000 people have received at least the first dose in the two-shot regimen.
It also helped that, unlike COVID-19, mpox is relatively difficult to spread. Most cases appeared to be spreading via sex, though other forms of close contact could also transmit it. That means that for most people, the risk of encountering the virus remained low.
Very little is known about whether people who have had monkeypox could face any long-term consequences. A small number of patients have developed eye problems, including vision loss, so doctors are advising people who have the virus not to wear contacts or touch their eyes until their rash has cleared up.
There isn’t much data on how long immunity lasts after vaccination or infection, though scientists think that people will be protected for at least a few years, Jacbosen said.
Of course, that doesn’t rule out the possibility that mpox could be reintroduced in unexpected ways, as it was in 2003 when pet prairie dogs that had been housed with imported animals spread the virus to their new owners in several Midwestern states, she said.
While some people have gotten mpox after being vaccinated, they generally reported less-severe symptoms, with lower odds of fever, muscle pain and a rash outside the genital area. They were also less likely to be hospitalized, according to the CDC.
Vaccines and immunity
So far, there doesn’t appear to be any difference in protection between those who received a smaller dose into the skin and those who got the vaccine the traditional way, though it’s possible that one group could see less durable protection, according to STAT News.
Early in the outbreak, the supply of vaccines was extremely limited, and slots at clinics filled almost immediately. By October, however, demand was dropping and supply was increasing enough that the state expanded the criteria for who could get the shots.
Now, anyone can get vaccinated if they or their sexual partners: had close contact with someone who has monkeypox; have multiple partners, or anonymous partners; had close physical contact in a venue where people have sex; were diagnosed with gonorrhea or syphilis in the past six months; have HIV; use medication to prevent HIV; or engage in sex for money, shelter or other benefits.
The state health department will send out reminders to people who haven’t gotten their second shot and has plans for an ad campaign later this winter on social media and dating sites to encourage vaccination, Herlihy said.
“Our priority is to make sure the people at increased risk are protected,” she said.
Right now, mpox isn’t as big a threat in the United States as COVID-19 or vaccine-preventable diseases like measles and pertussis, which are poised to resurge because many children haven’t gotten their shots over the last three years, Jacobsen said. Of course, it’s a different story in countries where the virus regularly circulates, which need sustained money and scientific attention to study it, she said.
“Within the community that had the highest risk profile, there is a high level of immunity,” she said.
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