Last week, the Centers for Disease Control and Prevention (CDC) issued a health advisory to physicians in the United States about a more transmissible strain of mpox virus spreading in the Democratic Republic of the Congo and asked them to consider mpox when evaluating rashes.
The alert was for clade I mpox virus, which is different than the clade IIb mpox virus at the center of last year’s global mpox outbreak.
Clade I has previously been associated with non-sexual routes of transmission, according to the CDC. Last month, however, WHO announced that it was spreading through sexual contact for the first time in the Democratic Republic of the Congo (DRC).
No clade I cases have been detected in the U.S. based on testing of roughly 12% of mpox cases reported in 2023, and the lack of direct commercial passenger flights from the DRC to the U.S. means the threat for travelers is low, according to the CDC, which nevertheless asked clinicians to be on the lookout for the virus.
Jay K. Varma, MD, executive vice president and chief medical officer at SIGA Technologies, said it is “very likely” the U.S. will see infections from this clade. Until recently, Varma led Cornell’s Center for Pandemic Prevention and Response.
“Given that there is ongoing human-to-human transmission in the DRC and likely other neighboring countries, it is only a matter of time before cases begin occurring regularly in other parts of the world,” Varma told Healio. “What remains uncertain for me and many others is the timeline. We do not know if this will happen in a matter of weeks, months or years, and we cannot predict where the cases will first arise.”
The CDC said clinicians should notify their health departments of any patient with mpox-like symptoms.
“Since the COVID-19 pandemic, the CDC is more quickly alerting clinicians and the general public to disease threats overseas, even if the risk of an epidemic in the U.S. is low,” Varma said. “I think this is part of a new general strategy by the CDC to not just detect events earlier but to also alert U.S. citizens as soon as possible.”
The global outbreak of mpox reached 111 countries, causing more than 92,000 infections, including more than 31,000 cases and 55 deaths in the U.S. The outbreak mainly spread via sexual transmission, mostly among men who have sex with men.
According to WHO, Since Jan. 1, 2023, there have been 12,569 reported mpox cases and 581 deaths (5% of suspected cases) in the DRC, with cases reported in 22 of 26 provinces in the country. Although household and community outbreaks have occurred in the country, this is the first time that clade I has spread among humans via sexual transmission.
Mpox vaccines are available, although coverage in the U.S. remains low, with just one in four eligible people receiving both recommended doses, according to the CDC. A study earlier this year showed that vaccination is 75% effective after a first dose, and that protection is boosted to 86% after a second dose.
Varma said it is unknown how long immunity from mpox infection or vaccination will last. He said there have been cases reported in people who have previously been vaccinated or infected, suggesting their protection may be limited to milder forms of disease rather than preventing infection.
Another challenge is that “new individuals become sexually active each day, such as teens or people coming out gay or bisexual and it is crucial to maintain continuous vaccination efforts to sustain high immunity levels,” Varma said.
According to the CDC, available treatments being used for clade IIb mpox infection including tecovirimat, brincidofovir, and vaccinia immune globulin are expected to also be effective against clade I infection.