Update on mpox: sleeping or hiding?

Simon Collins, HIV i-Base

For the first time in six months, this issue of HTB does not lead with a special report on mpox, previously called monkeypox.

From the first cases reported in the UK in May 2022, this normally rare infection rapidly spread to more than 100 non endemic countries, generating more than 85,000 cases and a global health crisis. By the end of the year, numbers dropped dramatically, even in countries with limited vaccine access.

Based on the recent WHO report, between 2 to 15 January 2023, 11 countries reported an increase in 7-day cases, with Mexico most affected, but still with only 59 cases. Importantly, 78 previously affected countries have not documented any new cases for over three weeks, the maximum incubation period. [1]

The most affected countries were the US (29,787 cases), Brazil (10,625 cases), Spain (7,505 cases), France (4,114 cases), Colombia (4,049 cases), the UK (3,730 cases), Germany (3,700 cases), Peru (3,698 cases), Mexico (3,696 cases), and Canada (1,460 cases).

Although sometimes mild, many cases involved considerable discomfort and pain and extremely severe cases, including necrosis, amputation, intensive care and approximately 30 deaths in the US. [2]

Mpox disproportionately affected people living with HIV, likely due to social and behavioural patterns that increased the risk of exposure than people on effective ART having a higher susceptibility. 

But many of the most serious cases were in people living with HIV, especially in those with low CD4 counts and detectable viral load, if not on ART, and the focus of an MMWR alert. [2]

This suggests that people not yet diagnosed might be at the highest risk, and late diagnosis remains a complex problem in nearly every country, reported in 40% or more of new diagnoses. [3] 

The risk of future outbreaks during 2023 is impossible to predict because of significant gaps in our understanding of the 2022 epidemic. 

Vaccine programmes only provided partial protection on a population level and vaccine efficacy was barely tested as case numbers were already falling due to early behavioural changes. Part of the decline is also being attributed to natural immune responses in those who were exposed but it is unclear how long either natural or vaccine induced immunity will last, with some studies suggesting that boosters might be needed within 6 to 24 months.

Unfortunately, mpox is likely to still continue in some countries, especially in central Africa where there is still no access to treatment or vaccines. There is also the potential for local outbreaks to occur, perhaps linked to international travel.


  1. WHO. Multi-country outbreak of mpox, External situation report number 14. (19 January 2023).–external-situation-report-14–19-january-2023
  2. Severe complication of monkeypox reported to the US CDC: risks associated with HIV and other causes of immunosuppression. HTB (3 October 2022).
  3. Collins, S,  Namiba, A,  Sparrowhawk, A,  Strachan, S,  Thompson, M,  Nakamura, H.  Late diagnosis of HIV in 2022: Why so little change? HIV Med.  2022; 23(11): 1118–1126. doi:10.1111/hiv.13444

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