As more monkeypox cases continue to emerge around the world, it's difficult to tell if or when the outbreak will end—but infectious disease experts offer three potential paths the virus might take in the United States.
According to CDC, more than 1,400 monkeypox cases have been reported in 33 countries since mid-May when the virus first appeared outside of its endemic region in Central and West Africa.
As of June 12, the United States has reported 49 confirmed and suspected monkeypox cases across 16 U.S. states and the District of Columbia. However, experts say this number is likely an undercount due to testing bottlenecks.
"The U.S. probably has as many cases as Canada or the U.K.," said Boghuma Titanji, an assistant professor of infectious diseases at Emory University. "We're just not testing enough to be able to reliably say that there are only  cases. I think we need to be testing way more than we're doing."
Although it is difficult to predict the trajectory of the monkeypox outbreak, infectious disease experts offer three potential paths the virus could take in the United States as cases continue to increase.
In 2003, monkeypox spread to 47 people in six states after infected pet prairie dogs were brought into the country. Within a few months, the spread of the virus was contained, and no deaths occurred.
This time, monkeypox appears to be spreading primarily through person-to-person contact, which makes controlling the outbreak more complicated, but experts say the outbreak is not likely to become a pandemic and the spread can still be contained through vaccination.
"Monkeypox is a containable virus," said Amesh Adalja, a senior scholar at the Johns Hopkins Center for Health Security.
Last month, CDC began releasing doses of Jynneos, a smallpox vaccine that has been approved to prevent both smallpox and monkeypox, from the U.S. emergency stockpile to select groups, including people who have had close contact with infected patients, health care workers, and people at high risk of developing severe illness from the virus.
According to The Atlantic, a tactic called "ring vaccination," in which close contacts of an infected person are vaccinated, helped contain the 2003 U.S. monkeypox outbreak, and Adalja said the same tactic could help control the spread of the virus in this current outbreak, with cases potentially falling to zero within three months.
"If we all react quickly and we all work together, we will be able to stop this," said Rosamund Lewis, the World Health Organization's technical lead for monkeypox. "We will be able to stop it before it reaches more vulnerable people and before it establishes itself as a replacement for smallpox."
Currently, monkeypox is only endemic in areas of Central and West Africa, but as it continues to spread, it could also become endemic in the United States, particularly if the virus jumps from humans to animals. In this situation, monkeypox could continue to circulate in wildlife even after there are no longer any human cases.
If monkeypox become endemic in animal populations, it could then jump from animals to humans and cause periodic outbreaks, much like what sometimes happens with anthrax, rabies, or bird flu. According to Bhargavi Rao, who worked in Africa as the head of emerging and infectious diseases at Doctors Without Borders, a minor monkeypox outbreak could cause occasional disruption and result in some animals being culled, but it is "not the sort of thing that overwhelms a community."
So far, Rao said the risk of monkeypox becoming endemic in animals outside of Central and West Africa is "very low," but the current outbreak may be different than the ones typically seen in Africa, since many cases have been occurring in cities rather than rural areas.
If an urban outbreak of monkeypox becomes large enough, the virus may become endemic in rodent populations, which could lead to other outbreaks later, according to The Atlantic. "When it's in the rats, there's nothing you can do," Adalja said.
Although there are tests, treatments, and vaccines for monkeypox, there is still a possibility that the current outbreak will not be contained and continue to spread, which could result in more severe illness, particularly in vulnerable populations.
"If you'd asked me two weeks ago, I would have anticipated that there might be a few thousand cases globally related to this current outbreak" before it ended, said Jay Varma, a population health professor at Weill Cornell Medical College. "But I've become much more pessimistic. … I would say it's less than 50 percent probability that we will contain this."
According to Varma, if the outbreak is not contained, monkeypox may continue to circulate at low levels, and cases may be concentrated among men who have sex with men (MSM), since many of the current cases have been found in this community. If this occurs, monkeypox could become like syphilis, which affects around 0.04% of Americans, most of whom are MSM.
In a worst-case scenario, which Varma says he believes is less likely, monkeypox could spread to the broader population and become as prevalent as genital herpes, which affects 12% of Americans. If monkeypox becomes widespread, it could have a significant impact on vulnerable populations, including children, pregnant individuals, and people who are immunocompromised, particularly those who have uncontrolled HIV.
According to Vox, around 13% of Americans with HIV are unaware of their diagnosis and are not being treated—a proportion that increases to over 20% in certain regions of the country. "This is the thing that worries me the most," said Gregg Gonsalves, an epidemiologist at Yale University's School of Public Health. "If there's a fifth of the HIV-positive community that doesn't know their status, it means they're at risk."
Ultimately, it is likely too early to say how the current monkeypox outbreak will unfold, especially since researchers are still studying whether the virus can be airborne and why recent cases have presented different symptoms than classic monkeypox.
"Every time a virus crosses species and gets into a new species, and it's transmitting itself and causing outbreaks, you are in a gray zone," which makes future outcomes more difficult to predict, Titanji said. (Gutman, The Atlantic, 6/9; Martichoux, The Hill, 6/9; Landman, Vox, 6/9)
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