For the second time in two years, the World Health Organization (WHO) has declared mpox (formerly known as monkeypox) a public health emergency of international concern.
The news follows an earlier global outbreak that spread into the United States in May 2022 and peaked in August of that year.
This latest outbreak is a new strain of mpox that is concentrated in the Democratic Republic of the Congo (DRC) and other African countries. It has not yet been identified in the U.S.
To find out more about mpox, the risks, and whether you should get vaccinated, we talked to Elizabeth A Talbot, MD, a specialist in infectious diseases and international health at Dartmouth Health.
What is mpox?
Mpox is a disease caused by infection with the monkeypox virus. The virus is thought to have started to circulate in parts of Africa in the 1950s. It is part of the same family of viruses as the variola virus, the virus that causes smallpox. There are two main strains, but so far, only the earlier strain has been identified in the U.S.
What are the symptoms of mpox?
Mpox symptoms in general are similar to smallpox symptoms but usually milder. The most common symptom is a rash that evolves to small firm nodules, blisters with clear then cloudy fluid, and then heals. It can be confused with other rash illnesses like chicken pox, syphilis, or shingles. The rash can be extremely painful, itchy as it heals, and leave scars. Other symptoms may include fever, headache, muscle aches, backaches, swollen lymph nodes, chills, and exhaustion.
This earlier strain has rarely been fatal, but people with weakened immune systems still have been at risk for more serious illness and sometimes death.
How is this new strain different and how will it impact the U.S.?
The new mpox strain is called Clade I, which is more easily transmitted, causes more severe infections, and has a higher mortality rate than Clade II.
As of September 2024, the newer Clade I strain had not been identified in the United States and so the CDC (U.S. Centers for Disease Control and Prevention) has said it does not know how Clade I will impact Americans, but it currently expects that the risk to most Americans is very low.
What is the status of the old strain in the U.S.?
The impact on Americans of the earlier strain, Clade II, seems contained. Since the start of the 2022 outbreak, there have been slightly over 32,000 reported domestic cases, with 60 deaths. That outbreak peaked in August 2022 and the CDC is no longer tracking the U.S. count due to low rates of transmission.
Mpox is most commonly transmitted to humans through close contact with an infected person and more rarely through contact with an animal or contaminated material.
Between humans, the mpox virus is usually transmitted by:
- Direct skin-to-skin contact (hugging, massage, kissing)
- Sexual contact
- Direct contact with saliva or respiratory secretions
- Prolonged face-to-face contact
A pregnant person also can pass mpox to the fetus during pregnancy or to the newborn during or after birth.
In addition, mpox can spread to anyone through contact with fabric, objects or surfaces that have not been disinfected after use by someone with mpox.
Is there an approved vaccine for both these mpox strains?
Yes. Regulatory authorities in the U.S., Europe and other high-income countries approved the JYNNEOS vaccine during the 2022 outbreak. The World Health Organization (WHO) also has just authorized the use of the vaccine in countries such as the Democratic Republic of Congo (DCR) and other low-income and middle-income countries.
Should you get vaccinated?
In the U.S., the CDC is not encouraging vaccination against mpox for the broader public or for everyone who is sexually active. However, you should talk to your doctor about getting vaccinated if:
- You have been identified as a close contact of someone with mpox.
- You learn that any sex partner in the past two weeks has been diagnosed with mpox.
In addition, you may want to get vaccinated if you are a man who has sex with other men or are a transgender or gender-diverse person who has sex with men and if any of the following apply:
- Having three or more new sex partners in the last month
- Engaging in group or anonymous sex
- Having sex at sex-on-site venues or events
- Taking medicine to prevent HIV (HIV PrEP)
What else is there to know about the vaccine?
The mpox vaccine is a two-dose series. The Department of Health in New Hampshire and Vermont can provide more information. While no vaccine is 100 percent effective, vaccination can reduce the chance of mpox illness and make the illness less severe.
Is there any new news from the CDC?
On September 23, the CDC issued a health update advising that regardless of their sexual orientation or gender identity, travelers to DRC or other countries with sustained spread of Clade I mpox should be aware of activities associated with cases and should be vaccinated with two doses of JYNNEOS if they anticipate certain sexual exposures.
Meantime, they reiterated that no domestic cases of Clade I mpox have been identified in the U.S. at this time and advised that people continue to follow CDC’s vaccine guidance to prevent Clade II infection, which continues to circulate in the U.S. and will also help protect against Clade I.
If you have further questions, contact your healthcare provider.