Younger People More Vulnerable to Mpox, Warn Epidemiologists

Young people are more vulnerable to catching mpox, epidemiologists have warned after the virus was declared a "public health emergency of international concern" by the World Health Organization (WHO).

At least 14 African countries have reported mpox outbreaks so far this year, with more than 17,000 suspected cases across the continent since the start of 2024, according to the Africa Centers for Disease Control and Prevention (CDC). More than 96 percent of all cases and deaths have occurred in the Democratic Republic of Congo, with many of those affected being children.

Mpox, formerly known as monkeypox, drew global attention in 2022 during an outbreak that affected the U.S., Europe, Australia and many other countries. The virus comes in two distinct forms, or "clades"—clade I and clade II—and spreads through close contact.

The previous outbreak in the U.S. and Europe was driven by the clade II form of the virus and was mostly spread through sexual and intimate contact, with men who have sex with other men being at the highest risk of infection.

In the past, clade I was not thought to be transmitted through sexual contact. However, a new version of the virus, called clade 1b, has now emerged which appears to be more transmissible than previous forms of the virus.

"In the past, we didn't know that clade I can be easily transmitted through sexual contact," Placide Mbala Kingebeni, Head of the Epidemiology and Global Health Division and Director of the Clinical Research Center at the National Institute of Biomedical Research in the DRC, said in a press conference. "Now, with clade 1b we see more sex workers affected and we are reporting more sexual activities being the main mode of transmission for this outbreak."

Because of the differences in transmission between clade Ia and clade Ib viruses, Kingebeni said we are seeing two different outbreaks occurring simultaneously in the same countries.

"One with clade Ia, where we see more children affected, and one which is this new clade Ib where we see more adolescents and adults affected," Kingebeni said. "The reason we are afraid about the clade Ib is because it seems to be very well adapted to human to human transmission."

It is noticeable that both variants of the virus are circulating significantly among younger members of the population—and experts think this might have something to do with their immune systems.

"I think that one of the underlying factors that has contributed to mpox in Africa were related to neglect of the disease for over 50 years and the lack of investments and low capacity to respond," Dimie Ogoina, a professor of infectious disease at Niger Delta University and a member of the WHO International Health Regulations Emergency Committee regarding the upsurge of mpox, said in the same press conference. "But one of the other biological reasons that could explain this outbreak is that the African population is relatively young, and to that extent we do not have the benefit of prior smallpox vaccination."

Smallpox was a serious, and often deadly, viral infection caused by an orthopoxvirus, the same family as mpox. The disease killed roughly 30 percent of those affected and is thought to have plagued humanity for thousands of years. However, in 1980 the Geneva-based WHO declared that, thanks to a successful, worldwide vaccination campaign, the disease had been eradicated.

After the 1970s, there was no longer a need for routine smallpox vaccinations. However, numerous studies have suggested that the smallpox vaccine may also confer some protection against mpox. As a result, those born before 1980 are likely to have some level of protection against mpox too.

"Orthopoxviruses share many proteins that are recognized by our immune system, and therefore infection with one orthopoxvirus confers protection against a subsequent infection with another orthopoxvirus," Jonas Albarnaz, a research fellow specializing in pox viruses at the U.K.'s Pirbright Institute, previously told Newsweek. "That's the basis of the smallpox—and now mpox—vaccine."

For this reason, experts also hope that existing mpox vaccines will also protect against the new clade Ib variant.

"It is really difficult to know exactly how different the virus of the clade 1b is from the viruses we've seen before," Mario Koopmans, Head of the Viroscience Department and Director of the Pandemic and Disaster Center at the Erasmus Medical Center in Rotterdam, said in the same press conference.

"Looking at the way the vaccines are designed, they are derived from vaccinia virus—that's a different pox virus—but that does confer cross protection, and that's been well documented with the clade II outbreak globally," he said. "It's not so easy to say exactly if this is full vaccine protection but the hope is that with 1b there would also be sufficient cross protection."

Despite the WHO's recent announcement, the U.S. Department of Health and Human Services says that the risk of clade I mpox to the U.S. population is low. Should clade I make its way to the U.S., the department said, it expects the virus would "cause lower morbidity and mortality in the United States than in the DRC."

However, it is important to continue disease surveillance should cases begin to rise in the U.S. and around the world.

As well as vaccination, the CDC recommends the following precautions to protect yourself from mpox:

• Avoid close contact with people who are sick with mpox symptoms, such as skin lesions, especially around the genitals.
• Avoid contact with wild animals in areas where mpox regularly occurs (for example, while traveling).
• Avoid contact with contaminated people and materials such as bedding and clothing used by people who are sick.

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References

Dee, K., Manali, M., Bissett, L. A., Bone, J., Magill, C., Davis, C., Willett, B. J., & Murcia, P. R. (2024). Smallpox vaccination campaigns resulted in age-associated population cross-immunity against monkeypox virus. Journal of General Virology, 105(6). https://doi.org/10.1099/jgv.0.001999