NBC News
As concern grows over a strain of monkeypox spreading through Africa that is believed to cause more severe complications, infectious disease experts are expressing cautious optimism that this strain of the virus will not spread as widely in the United States or cause as severe health impacts.
The risk of this subtype of the virus, known as monkeypox The spread of the novel coronavirus in the United States, abbreviated as mpox, could be mitigated by a number of factors, including immunity from vaccination and prior infection with the outbreak of a different variant that began in 2022, a lack of viral circulation in wild animals, and better access to health care.
On Wednesday, the World Health Organization reinstated monkeypox’s status as a public health emergency of international concern. This was done in response to a large ongoing outbreak of mpox clade 1. ―a clade is an evolutionary branch― in the Democratic Republic of the Congo, or DRC, which has spread to other African nations.
Sweden announced its first clade 1 case outside Africa on Thursday.
“It was only a matter of time before this spread beyond the African continent,” said Boghuma Titanji, an infectious disease specialist at Emory University.
In a statement on Friday, Pamela Rendi-Wagner, director of the European Centre for Disease Prevention and Control, said the agency had raised the risk level for clade 1 for the general European population from “very low” to “low.”
“Because of the close links between Europe and Africa,” Rendi-Wagner said, “we must be prepared for more imported cases of clade 1.”
The Centers for Disease Control and Prevention (CDC) confirmed Friday that there have been no reported cases of clade 1 in the United States to date.
Clade 1 is generally considered to be more transmissible and more severe than clade 2, which drove the global mpox outbreak that peaked in August 2022 and had a case fatality rate of 0.2%. Immunocompromised individuals, particularly those with advanced untreated HIV, have been at increased risk for severe complications, hospitalization, and death from clade 2. Low-level clade 2 transmission continues to be observed in the United States.
Anne Rimoin, an epidemiologist at the University of California, Los Angeles and a leading expert on mpox, said context is key when looking at how mpox might behave in Western countries compared with Africa.
“I think we have to be very, very cautious about saying it’s more dangerous,” Rimoin said of clade 1. “Data on severity and associated mortality are scarce. There are many questions about whether the perceived severity might have more to do with the population in which it spreads, their immune system, the route of transmission, the infectious dose.”
The National Institutes of Health reported Thursday that the antiviral drug TPOXX did not reduce the duration of clade 1 symptoms in a clinical trial in the DRC. But it is promising that only 1.7% of participants died, compared with a typical clade 1 death rate in the DRC of 3.6% or higher. Institutes experts praised the improved medical care provided to study participants.
Epidemiologist Jennifer McQuiston, who is responsible for the CDC’s mpox clade 1 response, said the study offered hope that High-quality health care in the United States would help minimize deaths from the disease.
Dan Barouch, a virologist at Harvard Medical School, said clade 1 cases were likely to occur in the country. “Currently, the absolute risk in the United States is low”he said. “Although we must remain vigilant.”
In December, CDC officials first alerted physicians and other health care professionals to be on the lookout for clade 1. The agency updated that advisory on August 7. When U.S. clinics request testing of possible MPOX specimens from patients with suspected cases, some testing sites test directly for the MPOX clade type, while others must send the specimens to CDC for testing. All positive results must be reported to CDC. Numerous sites across the country also test wastewater for signs of infection in the local population.
“We’re more concerned about clade 1 than clade 2,” McQuiston said of the CDC’s national surveillance.
The agency recently reported that receiving both doses of the Jynneos vaccine appears to reduce the risk of mpox. The CDC expects the vaccine to protect against both clades.
Throughout the now low-level clade 2 outbreak, mpox has overwhelmingly spread through sex between men. CDC continues to urge men with multiple male partners to receive both doses of Jynneos. Only an estimated 1 in 4 people considered at significant risk for mpox in the United States have been fully vaccinated.
The DRC outbreak has seen substantial sexual transmission of the clade, both among gay men and sex workers. Children, however, have accounted for two-thirds of the approximately 20,000 suspected cases and three-quarters of the 975 suspected deaths in the DRC since January 2023, according to the CDC.
The recently documented mutations of the virus may have made it more transmissible. Rimoin noted that close physical contact — whether sexual or nonsexual household contact — is likely still necessary for transmission.
People in the DRC tend to live in much smaller spaces than in the United States, according to Rimoin. “We have no news of people getting infected at the market”McQuiston said.
He added: “It is possible that domestic spread may occur in the DRC because family members care for the sick, and have less capacity to isolate the infected.”
The vaccine remains in short supply in the DRC. In the United States, where there is an adequate supply, household contacts of infected individuals can administer the vaccine prophylactically.
Rural residents in the DRC can also contract mucouspox from an unknown wild animal, perhaps a rodent. No animals in the United States are believed to carry the virus.
Jeffrey Klausner, an infectious disease expert at the University of Southern California, said in an interview that differences in sexual behavior between gay and straight people in the United States may continue to limit the spread of mpox among the general U.S. population.
Unlike heterosexuals, the general population of gay and bisexual men has a smaller group that engages in behaviors that could sustain an mpox outbreak outside of Africa, Klausner wrote in a commentary published in The Lancet Microbe on Aug. 7.
Klausner argued that infectious disease researchers have underestimated the rate of natural immunity from prior infection. For now, a combination of natural immunity and vaccine-induced immunity is sufficient among people with sexual behavior patterns more likely to transmit mpox to largely prevent a major outbreak.
However, while research suggests that natural immunity from the 2022 outbreak has persisted, it is possible that it will eventually wane and mpox may mutate to evade these defenses.
Furthermore, Chloe Orkin, an infectious disease expert at Queen Mary University of London, said: “It is unknown to what extent immunity to clade 2 viruses will protect people from infection or severe disease from clade 1 viruses.”
Emory researcher Titanji said of clade 1: “I don’t want people to get complacent and think that this can’t happen in a heterosexual network” in the United States.
