How Does Mpox Spread, and Who Is Most at Risk?

This month, the World Health Organization declared mpox a global health emergency. The virus, formerly known as monkeypox, is spreading quickly in parts of Africa, particularly the Democratic Republic of Congo. The outbreak there has been fueled by a new clade, or version, of the virus that has also been discovered in Sweden and Thailand.

The fast-evolving situation has led to anxiety and confusion about who is at risk of infection, and how the virus spreads. “I can understand why there’s concern,” said Dr. Taimur Khan, associate medical research director at Fenway Health, a medical center in Boston. But, he added, “it’s not like we’re being caught off guard in the same way that we were with Covid-19. It’s a virus that we are familiar with, to a certain extent, and we have tools already.”

We asked Dr. Khan and other experts to answer common questions about the virus.

What are we learning about how mpox spreads?

As the virus has evolved, so has our understanding about how it circulates, said Dr. Rosamund Lewis, technical lead of the World Health Organization’s global mpox response team.

In the 2022 outbreak, many cases were caused by sexual contact. The newer version of the virus continues to spread through sex, but experts said it is also circulating in other ways. Those could potentially include skin-to-skin interactions, contact with infected animals and touching contaminated surfaces, objects or fabrics, like bedding and clothes. Researchers are working to understand how the virus may spread through respiratory droplets and prolonged face-to-face interactions.

“We don’t always know exactly what was the mode of transmission in any given situation,” Dr. Lewis said.

Scientists are continuing to investigate when people are contagious. Some people can spread mpox days before they feel ill. No evidence to date indicates that people who never develop symptoms can spread the virus, according to the Centers for Disease Control and Prevention.