A new study from researchers in the U.K. suggests monkeypox spread may occur up to four days before symptoms surface, and that presymptomatic transmission might be more "substantial" than previously thought.
The findings were published Nov. 2 in the BMJ. Researchers examined data on 2,746 people diagnosed with monkeypox in the U.K. between May 6 and Aug. 1. Based on information from a subset of individuals who completed questionnaires, they identified 13 pairs between whom monkeypox was likely transmitted. There was evidence that monkeypox spread prior to symptom onset in 10 of those cases. Using mathematical models, researchers estimated 53 percent of cases may be transmitted presymptomatically.
Guidance from the CDC and other health agencies indicates the virus is transmitted after symptom onset. A CDC webpage last updated Oct. 26 says, "There is no evidence that monkeypox spreads from people with no symptoms," adding that "CDC will continue to monitor for new or changing information about transmission."
"It's an important and potentially controversial paper," Esther Freeman, MD, PhD, co-author of an accompanying editorial on the study and director of global health dermatology at Cambridge, Boston-based Massachusetts General Hospital, told The Guardian. "It provides evidence that there may be presymptomatic transmission of monkeypox going on. But like any modeling paper, it still needs to be reproduced and validated using other real-world data."
A key limitation of the study is that it depended on possibly unreliable recollections of sexual contacts and timing of symptom onset.
Two more monkeypox updates:
1. The World Health Organization and HHS said the outbreak still constitutes a public health emergency. HHS extended the nation's monkeypox public health emergency declaration Nov. 2, a day after the WHO said its emergency committee determined the global outbreak remains an emergency. Renewing the public health order in the U.S. ensures continued data flow between states and jurisdictions, and enables vaccine effectiveness studies, an HHS spokesperson told The Hill.
2. There have been nearly 29,000 confirmed cases in the U.S. as of Nov. 3, CDC data shows. The nation's seven-day daily case average has fallen significantly since August. On Nov. 2, the daily case average was 29, down from 423 on Aug. 15.