Experts Weigh In on Potential Impact of Emerging Mpox Clade
As a more severe strain of Mpox continues to spread across Africa, concerns are growing over the potential threat it could pose to the United States. However, infectious disease experts remain cautiously optimistic, believing that the U.S. may be able to mitigate the impact of this new clade.
The World Health Organization (WHO) recently reinstated Mpox, formerly known as monkeypox, as a public health emergency of international concern. This decision was driven by a large outbreak of clade I Mpox in the Democratic Republic of Congo (DRC), which has now spread to other African nations. Sweden announced the first case of clade I outside of Africa last week.
“It was only a matter of time before we saw this extend beyond the African continent,” said Dr. Boghuma Titanji, an infectious disease specialist at Emory University.
Mitigating factors in the U.S.
Several factors may reduce the risk of a widespread outbreak of this more virulent strain in the U.S. These include immunity from the 2022 Mpox outbreak of clade II, the absence of viral circulation in wild animals, and the U.S.’s robust healthcare infrastructure.
The Centers for Disease Control and Prevention (CDC) has confirmed that there have been no reported cases of clade I in the U.S. so far. However, the agency remains vigilant, having alerted healthcare providers to watch for potential cases and updated their advisory earlier this month.
“Although we need to remain vigilant, the absolute risk in the U.S. is currently low,” said Dr. Dan Barouch, a virologist at Harvard Medical School.
Clade I of Mpox is considered more transmissible and severe than clade II, which was responsible for the global outbreak that peaked in August 2022. Immunocompromised individuals, particularly those with untreated, advanced HIV, remain at the highest risk of severe disease and death.
Epidemiologist Anne Rimoin of UCLA emphasized the importance of context when assessing the threat of clade I. “We have to be very, very cautious about saying that this is more dangerous,” Rimoin said. “There are a lot of questions about whether the perceived severity might have more to do with the population it’s spreading in, their immune system, and the route of transmission.”
Global and domestic preparedness
The National Institutes of Health (NIH) recently reported that the antiviral TPOXX did not significantly reduce symptom duration in a DRC clinical trial for clade I. However, the study participants experienced a lower-than-average death rate, which NIH experts attributed to better medical care.
Dr. Jennifer McQuiston, who leads the CDC’s Mpox clade I response, expressed hope that the U.S.’s high-quality healthcare system would help minimize deaths if the virus were to spread domestically.
The CDC also noted that receiving both doses of the Jynneos vaccine appears to reduce the risk of Mpox, and they expect it to offer protection against both clades. Still, only an estimated 1 in 4 of those at significant risk in the U.S. have been fully vaccinated.
Broader implications and future concerns
The ongoing outbreak in the DRC has seen substantial sexual transmission of clade I, particularly among gay men and female sex workers. However, close physical contact, whether sexual or nonsexual, remains a likely transmission route.
In the U.S., differences in sexual behavior between gay men and heterosexuals could limit the spread of Mpox among the wider population, according to Dr. Jeffrey Klausner, an infectious disease expert at the University of Southern California.
While current immunity levels may help prevent a significant outbreak, experts warn that natural immunity from previous infections could eventually wane, and the virus may mutate to evade existing defenses. “The extent to which immunity from clade II virus will protect people from infection or severe disease from clade I virus is unknown,” cautioned Dr. Chloe Orkin of Queen Mary University of London.
Emory’s Titanji added a note of caution, saying, “I don’t want people to get complacent and think that we cannot see this in a heterosexual network” in the U.S.
As the situation evolves, health authorities continue to monitor the spread of clade I closely, prepared to respond should the virus reach U.S. shores.