Mpox, the disease formerly known as monkeypox, has been declared a global health emergency for the second time in two years by the World Health Organization, following a spike in cases in a growing number of countries in Central and West Africa.

The first outbreak in 2022 resulted in nearly 100,000 cases worldwide, including 32,000 cases and 58 deaths in the U.S. that mostly impacted gay and bisexual men. Transmission of this particular strain of the virus still occurs in small clusters in the U.S. today, averaging about seven new cases per week, according to CDC data.

Now a more severe and deadlier strain of mpox that first concentrated in the Democratic Republic of Congo has spread to more than a dozen other African countries and particularly impacted children less than 15 years old — although why that is remains unclear.

For people in the U.S., the overall risk is currently "very low," according to Dr. William Miller, an infectious disease specialist at Houston Methodist. Nonetheless, he stresses the importance of knowing your risk factors and getting the vaccine if eligible.

"Is it possible that the circulating strain could make it here to the U.S.? Absolutely," says Dr. Miller. "We're a plane flight away from many places in the world. But the people at the highest risk right now are going to be people who are traveling to the areas in Africa where the disease is endemic."

"For people living in the U.S., the vaccine recommendations remain unchanged at the moment, so for people with certain risk factors, they can talk to their doctor and potentially get vaccinated through the health department," he adds.

As the situation continues to develop, here's what you need to know so far about the latest mpox outbreak.

How is this mpox strain different than the one that caused the 2022 outbreak?

There are two main clades, or strains, of mpox: clade I and clade II. Clade I is the strain responsible for the current outbreak in the Democratic Republic of Congo; clade II, still circulating in small clusters in the U.S., is the strain that caused the outbreak in 2022.

Clade I is generally more severe than clade II, and has resulted in higher transmission rates, more severe symptoms and higher mortality rates. The currently reported mortality rates for clade I hover around 5%, compared to rates of 0.1%-3.6% for clade II during the 2022 outbreak.

According to Dr. Miller, however, clade I's reported mortality rate isn't necessarily reflective of what it might be like in a hospital setting.

"A recent trial of Tecovirimat, the antiviral medicine active against mpox, revealed that giving the medication didn't change how people survived clade I mpox compared to a placebo, but because everyone in the trial got supportive care, the overall mortality rate was 1.7%, much lower than the overall mortality rate being reported," says Dr. Miller.

"Clade I mpox is technically more severe, meaning more people are likely to get hospitalized, but if there were to be cases in the U.S., I don't think we would see the 5% higher mortality rates that are being reported," he says.

Who is at risk of getting infected with clade I mpox this time around?

As Dr. Miller mentions, individuals at the highest risk of contracting clade I mpox are going to be those traveling to the area in which it's endemic, Central and West Africa.

As for those in the U.S., Dr. Miller says the risk factors for clade II mpox remain unchanged for now, but those who are at risk should continue to get vaccinated fully by getting both doses. Those considered at risk include men who have sex with men, transgender, gender non-binary or gender-diverse individuals who have had sexual or intimate contact with another person at risk of mpox. You can read the CDC's detailed risk factor list here.

The big surprise about clade I mpox is the disproportionate effect on children, who comprise 67% of suspected cases and 78% of suspected deaths — numbers that public health officials are at a loss to explain; there was no such trend during the clade II outbreak. Dr. Miller emphasizes that so far, children in the U.S. aren't at "any particularly higher risk because the factors that we know are driving transmission here aren't related to children."

What are the symptoms of mpox?

The most notable symptom of mpox is a rash that can initially resemble pimples or blisters but that will go through several stages, including scabs, before it heals. Other symptoms of mpox can include:

• Fever
• Chills
• Swollen lymph nodes
• Muscle and back aches
• Fatigue
• Headache

The rash, as well as other symptoms, typically appear within 21 days of exposure to the virus. The incubation period (the time between exposure and onset of symptoms) is anywhere from 3 days to 17 days, during which a person may have no symptoms and feel fine.

(Related: What to Do if You Think You Have Mpox)

How does mpox typically spread?

Mpox can spread to anyone through close, personal contact (it does not have to be sexual contact); objects like sheets, bedding or towels that have come into contact with someone who has mpox (whether they had a rash at the time doesn't matter); and through infected animals, most often wild animals in Central and West Africa, where the disease is endemic; but it can also include house pets.

Those with mpox should avoid touching animals, including house pets, to avoid spreading the virus to them.

Are there cases of clade I mpox being reported in the US?

As of Aug. 30, 2024, there have been zero cases of clade I mpox being reported in the U.S., and overall risk for people right now in the U.S. is "very low," according to Dr. Miller.

What's still to be determined about this most recent outbreak?

"An interesting thing is it's not really one outbreak," says Dr. Miller. "It's actually several going on right now that have difference sources. Some cases have been from transmission from animals. There's a cluster ongoing from sexual transmission. Now there's been a large proportion of children affected."

What's driving this multi-factor outbreak? How much more will it spread and how quickly? Are recent isolated cases in Sweden and Thailand more "one offs" or are there going to be sustained strains of transmission? These are the questions Dr. Miller says experts have yet to answer, but thanks to the heightened awareness this time around from the CDC and World Health Organization, clinicians around the world should be more aware.

"Clade II took us by surprise, so I think people are going to be much more cautious about clade I this time around," he says.

What can you do to protect yourself from mpox?

Get vaccinated against mpox if you are eligible and make sure that you receive both doses at least 28 days apart for the best protection. It's never too late to receive the second dose. Studies show that one dose provides only 36%-75% protection versus 66%-89% protection with both doses.

Besides vaccination, however, there are a number of ways you can protect yourself from getting mpox:

• Wash your hands often with soap and water or use an alcohol-based sanitizer before eating, touching your face and after using the bathroom
• Consider changing your activities if you're at risk and haven't received the full two doses of the mpox vaccine
• Avoid contact with objects and materials that a person with mpox has used
• Avoid close, skin-to-skin contact with people who have a rash that looks like mpox
• Avoid touching the pets of someone who has mpox