Half of monkeypox transmission could be pre-symptomatic: Study

Jolyon Attwooll

3/11/2022 4:48:28 PM

Monkeypox transmission may be taking place up to four days before symptom onset, potentially impacting disease mitigation efforts.

Monkeypox case
Around 53% of all cases could be spread prior to people becoming aware of any symptoms, new research suggests.

‘Considerable’ transmission could happen with monkeypox before symptoms appear, new research published in The BMJ indicates.
The researchers, all from the UK Health Security Agency (UKHSA), based their work on details from a contact tracing study involving people with PCR-confirmed monkeypox from 6 May – 1 August this year, as well as a questionnaire to participants.
The article’s authors say 53% of all cases could be spread prior to people becoming aware of any symptoms – although they acknowledge that figure as ‘an approximation’.
Moreover, infected patients could cause transmission up to four days before symptoms showed, the study indicates, with authors also noting the potential implications for isolation guidelines.
‘If a substantial proportion of secondary transmission occurs before symptom onset, the implications will be that many infections cannot be prevented by isolating individuals with symptoms,’ they wrote.
‘Furthermore, the effectiveness of contact tracing will be affected because when contacts are traced, they might already have generated secondary cases.’
For the article, the researchers sought to measure the serial interval, described as the gap between the symptoms appearing in primary and secondary contacts, as well as the incubation period.
The average age of study participants was 37.8 years, with 95% of those reported to be gay, bisexual, or other men who have sex with men (1160 out of 1213).
By analysing the responses to contact tracing case questionnaires via statistical models and adjusting for bias, the authors estimate the mean incubation period at just over 7.5 days, while the serial interval took notably less time.
‘We found that shorter serial intervals are more common than short incubation periods for monkeypox, which suggests considerable pre-symptomatic transmission,’ the authors wrote.
They suggest an isolation period of 16–23 days would be needed to detect 95% of people with a potential infection.
They also reference limitations of the data, including a reliance on contact tracing to find the correct case-contact pairs, as well as self-reported data for measuring symptom onset. However, the researchers say their work is a ‘large study using robust methods’ and argue that even with widespread vaccination, their findings have implications for future disease spread.
‘Although case numbers are declining, increased international transmission would facilitate infection importation and might drive stochastic outbreaks even if vaccination in local networks limits transmission,’ they wrote.
Transmission peaked in the UK on 9 July, according to the study.

Official figures indicated that monkeypox transmission has also recently slowed significantly in Australia after an initial spike in the number of early cases – the first of which were detected in May this year.
According to the latest Federal Government statistics, there have been 140 probable or confirmed cases recorded in the country as of 27 October. Most of them have been identified in Victoria (69 cases) and NSW (54), with a handful in Western Australia (7), Queensland (5), the ACT (3) and South Australia (2).
The first cases in both Victoria and NSW were detected by GPs, who alerted local testing facilities.
The Government allocated significant funding to halt the transmission of the disease by in the most recent Federal Budget, with $73.9 million set aside for vaccines and treatments aimed at at-risk populations.
In a BMJ editorial accompanying the article, researchers say that more pre-exposure vaccination and vaccine equity are needed throughout the world.
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