I gave an mpox webinar yesterday, to focus on the new threat from the Clade Ib outbreak of mpox currently going on in the Democratic Republic of Congo (DRC), which has prompted the WHO to declare a public health emergency of international concern.

You can view the recording of the webinar below and download the slides here, but here’s a few things that struck me when I was preparing the webinar.

• There is a stark difference in the epidemiological presentation of the global Clade IIb outbreak of mpox in 2022 and the Clade Ib outbreak in Africa. Clade IIb was circulating mainly in gay, bisexual, and other men who have sex with men, whereas there seems to be a pretty much even gender split in the Clade Ib outbreak.
• There is very little published data to go by to understand the Clade Ib outbreak. I found a couple of useful articles on medrxiv (not peer reviewed of course), like this one.
• Mpox doesn’t seem to be that transmissible. If you measure it by R0 or secondary attack rate, whilst it does vary by clade, it’s substantially less transmissible that, say, measles or chickenpox, and less transmissible than SARS-CoV-2. For example, the secondary attack rate of mpox (across the different clades) comes out at about 0-10%, compared with around 20-40% for SARS-CoV-2 (review and meta-analysis of household transmission), and >50% for measles and chickenpox (nice review of transmissibility of respiratory viruses). Close, intimate, usually sexual contact seems to be the most important transmission route – and it’s of not that around one third of those involved in the Clade Ib outbreak are sex workers.
• Published case fatality rates are probably inflated. You may have heard a 10% CFR for Clade I mpox. Whilst this may be a fair analysis of the data, I don’t think it’s a true CFR because of limitations in surveillance. Also, I expect that fewer patients with mpox in a better resourced healthcare setting will have a bad outcome. Also, age seems to be an important factor – here’s a modelling pre-print showing that young children seem to have a considerably higher CFR than adults based on historic Clade I data.
• Whilst contact with the contaminated environment is a minor player in transmission based on epidemiological analyses, MPXV, the virus that causes mpox is more than capable of surviving on surfaces. Vaccina virus (from the same virus family) survive on dry surfaces for extended periods (>28d), and sampling of the hospital environment identifies high levels of MPXV DNA and culturable virus. Fortunately though, since MPXV is an enveloped virus, our usual range of hospital disinfectants will be effective.
• In terms of IPC management, mpox is ‘split’ into non-HCID mpox (Clade II) and HCID mpox (Clade I).
• Whilst community transmission of Clade Ib mpox seems unlikely at this stage or anytime soon, now is a really good time to prepare for an important case. How will you apply the case definitions for HCID and non-HCID mpox? Who will you test and how? Which PPE will you recommend for suspected and confirmed cases? How will you manage the contaminated environment?
• Finally, a few resources, which I found useful in preparing the webinar:
  • UKHSA mpox recommendations.
  • NHS mpox recommendations.
  • ECDC mpox recommendations.
  • CDC mpox recommendations.
  • WHO mpox recommendations.