WHO declares mpox a public health emergency of international concern

The World Health Organization (WHO) has classified mpox as a public health emergency of international concern following increasing case numbers in the Democratic Republic of the Congo and the risk that it could spread further.

The designation activates an internationally coordinated response to an exceptional event, alongside the deployment of resources including vaccines and diagnostic tests to limit the transmission of this infectious disease.

However, WHO has not said that mpox is a pandemic. Instead, these measures are intended to stop it developing into one.

What caused this latest alert?

Mpox, previously called monkeypox, is a viral illness closely linked to smallpox. Its early signs can include fever, headache, swollen lymph nodes and muscle pain. These are generally followed by a characteristic rash, chiefly affecting the face, hands and feet.

Mpox spreading across several African nations prompted the Africa Centres for Disease Control and Prevention to declare it a public health emergency of continental security earlier this week. It is the first such warning issued by the organisation since its creation in 2017.

For more than a year, the circumstances in the Democratic Republic of the Congo, in central Africa, have been especially concerning.

There are two forms, or clades, of mpox. Clade II, which began in west Africa, is the milder form. Its fatality rate can reach 1% (that is, approximately one in every 100 people may die). Clade I, which originated in central Africa, can have a fatality rate of up to 10% (up to one in ten people die). By comparison, the Omicron variant of SARS-CoV-2, the virus responsible for COVID, had a 0.7% fatality rate. The Democratic Republic of the Congo is experiencing major outbreaks of the more lethal clade I mpox.

In parts of central and west Africa, mpox is endemic: the virus is present in animals and may pass to people. Since 2017, outbreaks have grown, with increasing person-to-person transmission.

One reason is the very limited immunity to mpox, whose virus is related to the virus behind smallpox. Worldwide mass smallpox vaccination ended over 40 years ago, leaving present-day populations with little protection against mpox.

WHO's designation this week concerns clade I. Alongside its higher fatality rate, this clade has acquired new mutations that improve transmission between people. Those changes, combined with the worldwide absence of mpox immunity, leave the global population susceptible to the virus.

Two separate mpox epidemics

During 2022, an mpox epidemic spread through countries where it is not endemic, including nations outside Africa. It involved clade IIb, a clade II variant that originated in Nigeria. Transmitted sexually, it affected mainly men who have sex with men and had a low fatality rate.

That epidemic reached its high point in 2022, when vaccines were offered to at-risk people in high-income countries, although cases have risen again in 2024.

Meanwhile, the Democratic Republic of the Congo was experiencing large clade I epidemics that attracted considerably less attention.

Vaccines were unavailable there, including in 2023, when 14,626 cases and 654 deaths were recorded. The mortality rate was 4.5 percent and was greater among children.

Indeed, children account for most cases and deaths in the Democratic Republic of the Congo. This suggests that transmission there is mostly non-sexual, probably occurring through close contact or respiratory aerosols.

Yet an outbreak in 2023 in South Kivu, an eastern non-endemic area of the country, appeared to be sexually transmitted. This pointed to more than one epidemic in the Democratic Republic of the Congo, with distinct routes of transmission.

By the middle of 2024, the country had already reported more cases than in the whole of 2023: over 15,600 cases and 537 deaths.

The Democratic Republic of the Congo has limited testing capacity, and laboratory testing does not confirm most cases. Available information comes from a small set of genomic sequences sampled in the Kamituga area of South Kivu.

These reveal mutations in the clade I virus from around September 2023, producing a variant known as clade Ib that is more easily transmitted between people. There is little information with which to compare these viruses against those causing cases elsewhere in the country.

Mpox is spreading across borders

Over the past month, the virus has reached Rwanda and Burundi, countries bordering the Democratic Republic of the Congo. It has also appeared in other east African nations, including Kenya and Uganda. None of these countries had previously recorded mpox cases.

In a mobile, interconnected world, cases could reach other continents, just as mpox travelled from Nigeria to the United Kingdom and other countries in 2018.

A small number of travel-associated cases in 2018 and 2019 may have contributed to the major multi-country clade IIb epidemic of 2022.

Vaccines exist, but are not reaching those who need them

Because mpox and smallpox viruses are related, with both belonging to the orthopoxvirus group, smallpox vaccines protect against mpox. They helped bring the 2022 clade IIb epidemic under control.

Nevertheless, most people worldwide have never received vaccination and have no immunity to mpox.

The more recent vaccine, called Jynneos in some countries and Imvamune or Imvanex in others, is effective. Supplies are nevertheless constrained, and the Democratic Republic of the Congo has very little vaccine available.

WHO's declaration of mpox as a public health emergency of international concern should help direct vaccines to the places where they are required. The Africa Centres for Disease Control had already opened negotiations to obtain 200,000 vaccine doses, but this represents only a small proportion of the amount needed to control the epidemic in the Democratic Republic of the Congo.

What happens next?

In the end, a severe epidemic anywhere in the world matters to everyone, because international travel can carry it around the globe, as was seen during the COVID pandemic.

Containing the outbreak at its origin is the most effective approach, and WHO's latest declaration will support the mobilisation of the necessary resources.

It is also vital to monitor the spread of this more severe form of mpox, while recognising that many countries cannot carry out large-scale testing. Tracking the epidemic will therefore depend on "suspected cases", identified using a clinical definition.

Open-source epidemic intelligence can provide an additional early-warning tool, such as AI used to track patterns in rash and fever illnesses, particularly in countries with weak health systems or late reporting of cases.

Another difficulty is that 20-30 percent of people with mpox may also have chickenpox, a separate infection that likewise produces a rash. An initial chickenpox diagnosis, which is easier to test for, therefore does not exclude mpox.

Clear communication, as well as confronting resistance to public health measures and disinformation, is equally important. The COVID pandemic demonstrated just how crucial this can be.

WHO will now lead the global mpox response, with an emphasis on fairness in disease prevention and access to diagnostics and vaccines. Individual countries must make every effort to follow the International Health Regulations and the protocols governing the management of such a global emergency.

The World Health Organization has further information on mpox, including its symptoms and treatment. For details of vaccine access and availability, contact your local health department or doctor, as this differs between countries.

C Raina MacIntyre, Professor of Global Biosecurity, NHMRC L3 Research Fellow, Head, Biosecurity Program, Kirby Institute, UNSW Sydney

This article is republished from The Conversation under a Creative Commons license. Read the original article.