Vaccine profiles: mpox

Mpox had mostly been seen in West Africa until a global epidemic in 2022; the smallpox vaccine used to curb cases never made it to low-income countries that still need it.

  • 10 October 2023
  • 5 min read
  • by Gavi Staff
Monkeypox virus, one of the human orthopoxviruses, pathogen closeup (3d microbiology render)
Monkeypox virus, one of the human orthopoxviruses, pathogen closeup (3d microbiology render)


Factfile: mpox

  • Type: Virus
  • Symptoms: Fever, headache, muscle ache, swollen lymph nodes, chills and exhaustion, followed by a rash on the face, hands and feet, that can spread to the inside of the mouth, the genitals and the cornea.
  • Mortality rate: Up to 10% depending on the strain
  • Annual cases and deaths: Highly variable but in 2020, the Democratic Republic of the Congo has reported 6216 suspected cases and 222 deaths.
  • Geographical range: Mostly West and Central Africa, although 2022 saw a global outbreak in 111 countries.

Until 2022, mpox (formerly monkeypox) had only been seen outside the endemic areas of West and Central Africa when a traveller brought the smallpox-like virus with them. In May 2022, a case of mpox was detected in the UK, and soon several more – apparently unconnected – cases were found, spreading across borders in Europe and to the US.

This was unprecedented. Scientists puzzled over how a disease that wasn't thought to be easily transmissible was spreading so widely.  

Despite the 2022 global outbreak, the burden of disease remains highest in sub-Saharan Africa and South Asia.

African epidemiologists had been warning for a few years, largely unheeded by the rest of the world, that patterns of transmission seemed to be changing in countries with historical transmission of the virus. And in 2022, for the first time, the virus seemed to be spreading easily between people in non-endemic countries.

It soon emerged that most of the cases across Europe and the US were in men who have sex with men, especially those who had closely connected sexual networks, allowing the virus to spread in a way it hadn't in the general population.

By July 2022, the World Health Organization (WHO) declared the global outbreak a Public Health Emergency of International Concern (PHEIC), a move intended to galvanise action to respond to the emergency. Mpox is closely related to smallpox, and the smallpox vaccine that can prevent about 85% of mpox cases was deployed to curb transmission.

However, the vaccine supplies were used almost entirely in high-income countries. Today Africa has still not received a single dose. By the time WHO declared the end of the PHEIC in May 2023, more than 87,000 cases and 140 deaths had been reported from 111 countries.

Meanwhile since 2018, the Democratic Republic of the Congo (DRC) has reported more than 3,000 suspected cases per year, with a peak of 6,216 suspected cases and 222 deaths in 2020.

In 2017, Nigeria saw a re-emergence of cases after nearly four decades of zero cases; this outbreak culminated in May 2018 with 122 confirmed or probable cases in 17 states, including seven deaths. The country has continued to report mpox cases, most of which are concentrated in the most southern states, including in urban settings.

Despite the 2022 global outbreak, the burden of disease remains highest in sub-Saharan Africa and South Asia.

History of the virus

Mpox and smallpox are members of the Orthopoxvirus genus in the family Poxviridae. Mpox was first discovered in 1958 when outbreaks of a disease that caused pox-like symptoms were discovered in monkeys held in captivity for research. It was first seen in humans in 1970 in the Democratic Republic of the Congo (DRC) and it is now endemic in Central and West Africa.

People can get infected either through contact with animals – for example via infected rodents through broken skin (bites or scratches), or direct contact with an infected animal's blood, bodily fluids or pox lesions (sores)​. The virus can also spread between people, through skin-to-skin contact with sores, scabs, respiratory droplets or oral fluids, usually through close, intimate situations.

Early symptoms include fever, headache, muscle ache, backache, swollen lymph nodes, chills and exhaustion. Once a fever has appeared, a rash tends to follow, mostly on the face, hands and feet before spreading to other areas of the body. It can spread to the inside of the mouth, the genitals and the cornea.

The rash progresses until it forms a scab which falls off, and in some cases large sections of skin can drop off the body. Symptoms normally appear between five and 13 days after infection, although it can take up to 21 days for them to appear.

Mortality rates depend on which type of mpox is causing the infection. There are two groups or 'clades'; with clade I infections, one in ten cases can be fatal. People infected with clade II are far less likely to die, however, people with severely weakened immune systems, babies younger than one year of age, and people who are pregnant or breastfeeding may be more likely to get seriously ill or die. These groups are also less likely to receive a vaccine, given that the currently licensed vaccines against mpox are not approved for use in these parts of the population.

Mpox vaccines

Two vaccines, Jynneos (Bavarian Nordic) and ACAM2000 (Emergent Biosolutions), have been licensed in the US, Canada and Europe for mpox, both for people older than 18. LC16m8, an attenuated, replicating smallpox vaccine is currently licensed in Japan for both children and adults. However, it's not clear yet how long immunity lasts.  

BioNTech, in partnership with CEPI (Coalition for Epidemic Preparedness Innovations) is starting a Phase 1/2 clinical trial of the mRNA-based mpox vaccine candidate, BNT166.

Potential challenges in vaccine rollout

Currently, getting a clear picture of how mpox is circulating is challenging in low- and middle-income countries because surveillance is difficult and characterised by under-reporting of cases. Diagnosis of mpox is also challenging as the symptoms can look similar to chickenpox or other pox-causing diseases, and thus molecular diagnostics are needed, which are unlikely to be available in rural parts of Africa.

Another factor hindering a good understanding of the virus's behaviour is stigma, since the global outbreak was largely driven by sexual transmission. This renders contact tracing and case reporting difficult, resulting in incomplete and poor-quality data from the African region.

Furthermore, vaccine deployment will require the identification of at-risk populations at the community level that would need to be targeted for immunisation, as mass vaccination against mpox is currently not recommended.