Clinical efficacy of tecovirimat for treatment of mpox in people living with HIV

Simon Collins, HIV i-Base

Guidelines for the clinical management of mpox infection include the recommendation in severe cases to use tecovirimat, an antiviral against smallpox, while recognising the limited evidence.

Results from a prospective cohort study provide new data supporting the early use of tecovirimat within seven days of mpox symptoms.

The study included people living with HIV who were diagnosed with mpox between June amd October 2022 at four HIV clinics in Atlanta, Georgia. Multivariable regression analysis was used to identify factors associated with mpox progression.

Participants were divided into those who received tecovirimat within seven days of the first mpox symptoms (n=65) or those who either received it later or not at all (n=197). Propensity scores were used to match 112 participants (n=56 from each group) using a primary outcome of progression of mpox symptoms after day seven.

The median time to starting tecovirimat in the early group was 4 days (IQR: 3 to 6); 20 individuals received tecovirimat in the late group at a median of 10 (IQR:9 to 15) days after the first symptom.

Approximate baseline characteristics included median age 45 (IQR: 30 to 43). 96% cisgender men, 85% Black ethnicity, balanced between the two groups. Roughly 40% in each group (n=22) had detectable HIV viral load >200 copies/mL.

Although CD4 count was not used when matching, this was lower in the early tecovirimat group (median 314 vs 433 cells/mm3, respectively).

Mpox disease progression occurred in 3 (5.4%) vs 15 (26.8%) individuals in the early vs late/no groups respectively. This represented an odds ratio for progression of 11.0 (95% CI: 1.4 to 85.1), p=0.002 with late/no vs early tecovirimat.

The median time to symptom progressions was also significantly longer for those using early tecovirimat: median 22 days (IQR: 4 to 57) vs 4 days (IQR: 2 to 12), respectively.

The authors concluded that even though this was a small study with limitations of the matched design, these results supported early use of tecovirimat in all people living with HIV as soon as mpox is suspected. Although side effects were not reported, other larger studies have reported good tolerability.

However, an editorial comment on the paper suggested that a more cautious approach might still be warranted before universally prescribing tecovirimat to everyone with mpox, given the limitations of observational data and limited access to tecovirimat. The potential for confounding and the wide confidence interval for the primary endpoint was also noted. [2]


Current recommendations for access, including by the US CDC, are based on severity of mpox and risk factors that increase the risk of a severe outcome. More limited access also supports the importance of prioritising access to those with a low CD4 count (<200 cells/mm3) or detectable viral load.

Limiting access also enables enrolment into the ongoing randomised studies of tecovirimat that will produce a more reliable dataset and definitive evidence about efficacy.

Of note, neither publication referred to the lack of susceptibility testing for the development of tecovirimat resistance, with is an additional concern on an individual and population level.

A recent paper in PLoS usefully reviews some of the difficulties faced by international tecovirimat studies. This includes the lack of a fast-track approval process, apparently learning little from the experiences of COVID-19. It also highlights how the drive for research is still closely tied to potential commercial outcomes in high-income countries. [3]

  1. Early Tecovirimat Treatment for Mpox Disease Among People With HIV. JAMA Internal Medicine Research. (8 January 2024).
  2. Tecovirimat for Mpox—Promise and Limitation. JAMA Internal Medicine. Opinion. (8 January 2024).
  3. Olliaro P et al. (2024) Mpox: The alarm went off. Have we gone back to sleep? PLoS Negl Trop Dis 18(1): e0011871.

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