Scientists assess potential of monkeypox transmission at mass gatherings

In a recent study posted to the medRxiv* preprint server, researchers assessed the potential of monkeypox transmission at mass gatherings.

Since May 2022, several non-endemic countries have reported monkeypox infections. Moreover, owing to the strict measures undertaken due to the coronavirus disease 2019 (COVID-19) pandemic over the past two years and the collective desire of the general public to regain their normal lives, mass gatherings held in Summer 2022 are expected to be very crowded.

Social contact and mass gatherings

In the present study, researchers explored the likelihood of monkeypox transmission at settings and venues of mass gatherings that would facilitate infection spread.

Many social and mass gatherings such as music festivals like Glastonbury in the UK, the Zurich Street Parade in Switzerland, and Summerfest in Wisconsin are held in the summers and have an attendance of between 200,000 and 850,000 people. Since restrictions related to COVID-19 were imposed in 2020 and 2021 led to either event cancellation or restricted attendance, these events are expected to be highly attended in 2022.

Social contact surveys showed that the average number of contacts recorded on a Saturday in Germany was 19.5 while in the UK it was 20.3. Additionally, social mixing patterns observed at an event were calculated using video analysis. An experiment that measured the direct contact incidents in an indoor mass gathering of almost 1,100 attendees revealed contacts with 8.9 to 14.1 distinct persons for more than 15 minutes and five minutes, respectively.

Human-to-human monkeypox transmission

The increasing number of monkeypox infections reported in endemic countries along with the current monkeypox outbreaks in non-endemic countries indicated the potential of monkeypox transmission from human to human. The team estimated the basic reproduction number (R₀) from endemic countries using previous years’ data wherein a large percentage of the population had received the smallpox vaccine. Taking this into account, R₀ within a completely susceptible population was found to be approximately 2. Furthermore, secondary attack rates (SAR) estimates could be used to estimate the R₀ value.

R₀ for monkeypox in mass gatherings

The team investigated the potential of monkeypox transmission among humans in a mass gathering under several scenarios, considering the number of close contacts. The researchers assumed that one infectious individual attending such a mass event would have two to 10 contacts including family and friends as well as five to 50 other contacts. In this scenario, the R₀ was calculated using estimates of the SAR for unvaccinated individuals. The team also employed SAR estimates for household persons for close contacts as well as non-household persons for contacts with fellow attendees. The simulations performed showed that the SAR for unvaccinated close contacts was 7.57 and that for unvaccinated other contacts was 2.69.

The simulation results showed that the mean R₀ could increase to 2.1 for individuals having a high number of close as well as other contacts. Notably, R₀ could be more than one for an infectious person who had contact with more than 30 individuals, even if that person had close contact with only two or three persons. Moreover, having contact with eight to 10 people could result in more than one secondary infection case even if the person had less than 15 other contacts.    

Overall, the study indicated that enforcing awareness and timely detection of the monkeypox virus is imperative to control infection transmission and curb its spread.

*Important notice

medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.

Written by

Bhavana Kunkalikar

Bhavana Kunkalikar is a medical writer based in Goa, India. Her academic background is in Pharmaceutical sciences and she holds a Bachelor's degree in Pharmacy. Her educational background allowed her to foster an interest in anatomical and physiological sciences. Her college project work based on ‘The manifestations and causes of sickle cell anemia’ formed the stepping stone to a life-long fascination with human pathophysiology.