Simianpox transmission dynamics in the UK: contact tracing study Main findings The global transmission of monkeypox since May 2022 in non-endemic countries required greater understanding of the transmission dynamics of the virus. The mean incubation period and mean serial interval were found to range from 6.6 to 9.2 days and 7.4 to 12.3 days, respectively, when adjusted for right truncation and epidemic phase bias. . The median serial interval was estimated to be shorter than the incubation period, indicating considerably greater presymptomatic transmission than previously thought, and was validated by analysis of individual-level data. Analysis of the instantaneous growth rate indicates that as of July 9, the epidemic peaked in the United Kingdom. Although the number of cases is decreasing, increased international transmission would facilitate the importation of infections and could lead to stochastic outbreaks even if vaccination in local networks limits transmission. |
A UK study published in The BMJ found evidence of "substantial" monkeypox transmission before symptoms appear or are detected (known as pre-symptomatic transmission).
Transmission was detected up to four days before the onset of symptoms, and researchers estimate that more than half (53%) of transmission occurred in this pre-symptomatic phase, meaning that many infections cannot be prevented by asking people to isolate themselves. after you notice your symptoms.
In a linked editorial, the researchers say that if these findings are supported by other studies, presymptomatic transmission "would have important implications for global infection control."
Since the international monkeypox outbreak in May 2022, more than 70,000 cases have been recorded worldwide, with just over 3,500 cases in the UK.
Although the number of cases is now declining, it is still important to understand the "transmission dynamics" of the virus - for example, how it spreads from person to person and how quickly symptoms appear - to help inform policy decisions and policies. future interventions.
While previous research on smallpox viruses did not rule out transmission before symptoms, this work represents the first evidence to support this.
To explore this further, researchers at the UK Health Security Agency set out to analyze the transmission dynamics of the monkeypox outbreak in the UK.
Their findings are based on routine surveillance and contact tracing data from 2,746 people who tested positive for monkeypox virus in the United Kingdom between May 6 and August 1, 2022. Their average age was 38 years old and 95% reported being gay, bisexual, or men who have sex with men.
The two main measures of interest to the researchers were the serial interval (time from the onset of symptoms in the primary case patient to the onset of symptoms in the secondary contact) and the incubation period (time from exposure to the onset of symptoms).
To estimate this, they linked exposure information and symptom onset dates of these people to their contacts through contact tracing case questionnaires, which they then analyzed using two statistical models.
The models were adjusted for several biases common to virus outbreaks, such as changes in infection rates over time, that would otherwise affect the results.
The mean incubation period was estimated to be 7.6 days in one model and 7.8 days in the other model, while the estimated mean serial interval was 8 days in one model and 9.5 days in the other.
For both models, the median serial interval was 0.3 to 1.7 days shorter than the median incubation period, indicating that considerable transmission is occurring before the onset or detection of symptoms.
Analysis of individual-level patient data, collected from a subset of patients with more detailed information, appeared to confirm this explanation, with 10 of 13 case-contact patient pairs reporting presymptomatic transmission. Four days was the maximum time transmission was detected before symptoms appeared.
Based on these results, the researchers say an isolation period of 16 to 23 days would be required to detect 95% of people with possible infection.
These are observational findings, and the researchers point out several limitations, such as relying on contact tracing to identify the correct case-contact pairs and self-reported data on the date of symptom onset. Furthermore, the results may not necessarily be directly applicable to other populations with different transmission patterns.
However, this was a large study that used robust methods and adjusted for key biases present in the data, providing greater confidence in the conclusions.
These findings have important implications for isolation and contact tracing policies, the researchers say, adding that backward contact tracing strategies (tracking who the disease is spreading) should take into account a pre-symptomatic infectious period when trying to find the contacts of confirmed cases.
In a linked editorial, researchers based in the US, UK and Nigeria argue that pre-exposure vaccination and vaccine equity are urgently needed around the world.
Vaccination is likely to be more cost-effective than controlling the consequences of preventable infections, including hospital admissions, loss of income during isolation and long-term complications, they explain.
However, they note that many of the public health measures that have been critical during monkeypox outbreaks in high-income countries remain unavailable in much of Africa.
“As the monkeypox outbreak subsides in Europe and North America, we have a responsibility to implement effective tools for viral control globally, not just in wealthy nations,” they write.“These tools include research to understand transmission dynamics in African settings and the inclusion of endemic countries in vaccine trials.”
Conclusions Global transmission of the monkeypox virus has been on a scale never before seen outside of Central Africa. The shorter median estimate for serial interval relative to incubation period suggests that presymptomatic transmission may be more important than previously thought, which is supported by linked patient-level data. The 95th percentile of the serial interval ranged from 23 to 41 days, suggesting a potential for long infectious periods that are consistent with research on previous clades. In the present study, the incubation period, ranging from 16 to 23 days post-exposure, would be adequate to identify 95% of infected individuals, as well as the required duration of post-exposure isolation policies. |
What is already known about this topic?
- Monkeypox was first detected in 1970 in the Democratic Republic of the Congo.
- The incubation period and series interval have been estimated from observational studies.
- Since the international monkeypox outbreak in May 2022, one study estimated a median incubation period of 8.5 days; however, the sample size was small (n=18).
What this study adds
- This study found evidence of presymptomatic monkeypox transmission , using contact tracing data and adjusting for interval censoring, right truncation, and epidemic phase bias.
- The maximum time transmission was detected before symptoms appeared for infected individuals who could be linked through reliable personally identifiable information was four days.
