An escalating mpox outbreak is causing alarm among some health experts, who warn that the latest strain of the virus could be more fast-spreading and deadly than an early 2022 outbreak.

The World Health Organization last week declared mpox a global public health emergency following the spread of an outbreak in the Democratic Republic of Congo (DRC) to neighboring countries.

Since the new outbreak, cases have been identified in countries where mpox is not endemic, such as Sweden, Pakistan and Thailand — although its unclear which strain has been unidentified in some of these nations.

Mpox is a viral infection which spreads through close contact and causes flu-like symptoms and lesions filled with pus. While usually mild, it can be fatal.

The WHO’s director for Europe, Dr. Hans Kluge, said Tuesday that the outbreak is “not the new Covid” and that it can be stopped with international cooperation.

But health experts have warned of the “many unknowns” surrounding the latest outbreak — and in particular a new subvariant — which could make it harder to contain.

“Clade 1b has recently emerged and there are many unknowns that need to be addressed,” said Trudie Lang, professor of global health research and director of The Global Health Network at the University of Oxford.

“There is emerging evidence of differences in transmission and symptoms; such as more commonly passed person to person and from mothers to their babies in pregnancy,” she said.

There are broadly two types of of mpox, known as clades, with the latest outbreak identified as clade 1. Compared with the 2022 strain, clade 2, the current strain, appears to spread more easily and has a higher fatality rate.

A newly identified clade 1b subvariant has been found to be particularly prevalent among young people and appears to be spreading through sexual networks, Jonas Albarnaz, a research fellow specializing in poxviruses at The Pirbright Institute, said.

However, he noted more data is needed to understand its transmission dynamics and to “inform the control strategies.”

More vulnerable countries

Clade 1 is already known for causing more severe disease in young children, pregnant women and immunocompromised people. That has hastened the outbreak in countries where certain health conditions are more prevalent and those with poorer health-care systems.

“As mpox disease is more severe in immunocompromised individuals, it is also a concern that the current outbreak is taking place in a region where HIV prevalence is relatively high but access to antiretroviral drugs is poor,” said Brian Ferguson, associate professor of immunology at the University of Cambridge.

Ongoing conflicts in parts of Africa — such as the DRC, where a large number of displaced people have relocated to refugee camps — have also worsened sanitation conditions and accelerated the spread.

So far this year, more than 15,000 cases and at least 537 deaths have been reported from the outbreak in the DRC, according to the WHO, with more cases reported elsewhere.

Ferguson said that more cases are likely to be identified in the coming days and weeks given the lack of controls in place to prevent the spread from country to country. He also said that lessons had not been learned from the prior outbreak, which was declared a public health emergency in July 2022 before the designation was removed in May 2023.

“The lack of activity in the intervening period has resulted in what could now become a new global outbreak. There should have been a greater effort to produce and distribute vaccines to the affected areas, but this has not happened,” he said.

Vaccines for younger people

Danish biotech firm Bavarian Nordic, one of the only companies with an approved mpox vaccine, said Tuesday that it would decide this week whether to ramp up production of its jab even before having orders lined up, according to Reuters.

That comes after the company on Friday submitted data to the European Union’s drug regulator to extend the use of its mpox vaccine for adolescents.

CEO Paul Chaplin told CNBC at the time that obtaining approval for 12- to 17-year-olds would be crucial in tackling the outbreak of the latest strain of the virus.

“More than 70% of the cases in Africa currently are in people younger than 18, so it’s going to be critical that our vaccine can be used in this younger age group,” he said.