There is evidence pointing to a “considerable” transmission of monkeypox in the several days before symptoms of the virus emerge, a contact tracing study in the UK has revealed.Routine surveillance data on 2,746 people diagnosed with monkeypox in Britain between May 6 and August 1 and collected by the UK Health Security Agency (UKHSA) had been examined by the research team.The UKHSA investigators involved in the study, details of which were published in the British Medical Association journal (BMAJ) on November 2, analyzed questionnaire data to estimate the monkeypox incubation period. They also scrutinized data to estimate the so-called ‘serial interval’. The latter is the timeframe between one individual’s first symptoms and the onset of symptoms in a person to whom they likely passed the virus.Resorting to various mathematical models, the team found that the average serial interval was 0.3 to 1.7 days shorter than the median incubation period, which was typically a week. Accordingly, the scientists concluded that a “substantial” number of cases (an estimated 53 percent) were transmitted presymptomatically.After detailed analysis of 13 pairs of individuals between whom monkeypox likely transmitted, ten of the cases appeared to show presymptomatic transmission having occurred. In other words, the virus was likely to have been transmitted from one person to another a maximum of four days before any symptoms were displayed.Meanwhile, the US Centers for Disease Control and Prevention (CDC) guidance on monkeypox says that people “can spread it to others from the time symptoms start until the rash has fully healed,” indicating that to date “there is no evidence that monkeypox spreads from people with no symptoms.”Monkeypox is a rare viral disease that occurs predominately in Central and West Africa, with most people recovering in a few weeks. Early symptoms include rash, fever, headache, muscle aches, backache, swollen lymph nodes, chills and exhaustion. Across the globe, 77,174 people have been found to have contracted the disease in 109 nations, including 28,442 in the US, according to the CDC. Since the first patient tested positive for the disease in early May, 3,439 confirmed and 146 highly probable monkeypox cases were registered in the country up to September 16, 2022. UKHSA has reported a slowing of monkeypox cases in Britain since August 15.