Early Launch – Characteristics and Transmission Dynamics of International Travel-Associated Mpox Instances Attributable to Clade Ib Monkeypox Virus – Quantity 32, Number 2—February 2026 – Rising Infectious Illnesses journal

By June 19, 2025, MPXV clade Ib had been reported from 14 nations in Africa. Travel-related circumstances, as outlined by WHO (5), have been reported from 19 nations outdoors of Africa and led to secondary circumstances in 8 of the vacation spot nations.

Figure 1

Figure 1. Transmission dynamics amongst world travel-related mpox circumstances brought on by clade Ib monkeypox virus. Yellow dots characterize nation of publicity; arrows characterize course of journey for mpox circumstances reported as of…

We used case knowledge that was shared with WHO below the provisions of the International Health Regulations (2005) (6) or revealed individually. We collated knowledge from 127 mpox circumstances, 124 confirmed and three suspected; 89 have been travel-related, 34 have been secondary, and 4 have been unlinked. Of the 89 travel-related circumstances, 70 case-patients reported having been uncovered in Africa and 18 outdoors Africa; 1 had unknown publicity origin (Figure 1). All imported circumstances have been amongst adults, besides 1 of unknown age (lacking knowledge); 88 circumstances had intercourse knowledge accessible, 67 (76%) have been males and 21 (24%) have been girls; 25 travel-related circumstances led to 34 secondary circumstances within the nation of notification, together with circumstances amongst 6 males, 19 girls, and 6 youngsters (<17 years of age). Among secondary circumstances, 15/25 (60%) adults reported sexual contact or probably sexual contact with the index case (i.e., unspecified contact with the index case’s companion).

Figure 2

Figure 2. Characteristics and transmission dynamics amongst world travel-related mpox circumstances brought on by clade Ib monkeypox virus. A) Sankey diagram of secondary transmission occasions amongst 33 transmission occasions and secondarily contaminated individuals….

Of the 33 secondary circumstances with knowledge accessible for each index and secondary circumstances, most (73%) resulted from males, who transmitted MPXV to principally girls and kids, adopted by girls (21%), who contaminated principally males and kids. Secondarily contaminated youngsters (6%) contaminated 1 youngster and 1 man (Figure 2, panel A). Using 14 case pairs, we estimated that the imply serial interval (SI) for an infection was 12 (95% CI 4–27) days. We estimated that the SI for sexual and sure sexual contact was 9 (95% CI 5–14) days, which was shorter than the SI for nonsexual family contact, 15 (95% CI 8–29) days (Figure 2, panel B). That SI distinction may partly be due to the shorter incubation interval and better infectious dose for sexual transmission (7; F.Okay. Kaiser et al., unpub. knowledge., https://doi.org/10.1101/2025.08.14.669880).

Contact knowledge have been accessible from 50 circumstances, and we have been capable of disaggregate threat standing of contacts for 32 of these circumstances. We outlined high-risk contacts as family members, sexual contacts, or each. When no additional data was accessible, reporting nations outlined high-risk contacts. Using these knowledge, we recognized a complete of 74 high-risk contacts from 33 circumstances, 1 of which didn’t have sufficient data accessible to disaggregate additional into contact sort (Figure 2, panel C). Of the 25 major circumstances from whom secondary transmission was reported, a median of 1 (vary 1–4) secondary case occurred. We estimated the SAR for family contacts was 17% (95% CI 8%–31%) and for sexual contacts was 73% (95% CI 39%–94%) (Figure 2, panel D). No secondary circumstances have been reported amongst group contacts or contacts in healthcare settings.

The first limitation of our evaluation is the small pattern measurement as a result of data was lacking for some circumstances. Second, the sexual contact SAR is primarily restricted to transmission between spouses or companions, and the excessive estimate would possibly mirror repeated sexual publicity, extended shut contact throughout the family, or each, along with a attainable underreporting of sexual contacts outdoors the family. Finally, travel-associated circumstances could possibly be missed, particularly in nations the place mpox is strongly stigmatized, and our estimates won’t be generalizable past the settings described.

Our outcomes spotlight that shut contact is a key driver of MPXV clade Ib outbreaks and present that sexual contact carried the best transmission threat, adopted by family contact. We discovered no proof of an infection threat past settings the place contact was probably shut and extended. Other research have additionally acknowledged the function of sexual contact as essentially the most environment friendly MPXV transmission route (8,9). Of be aware, secondary family circumstances have been recognized in the course of the MPXV clade Ib outbreak reported right here, however in the course of the 2022–23 clade IIb outbreak, such occasions have been uncommon; earlier than August 2024, WHO recorded solely 15 (0.2%) of seven,794 mpox circumstances in youngsters <15 years of age amongst these uncovered within the family (knowledge not proven). Whether that disparity displays variations in family and social contact buildings or intrinsic viral properties stays unclear. The greater threat related to sexual publicity and family contact ought to inform response methods and precedence interventions for populations most in danger.