The First Year of CDC's Mpox Response, 2022–2023

Summary

• Mpox was first detected in the U.S. in May 2022; cases rose fast and peaked in August, spread mainly through sexual contact among gay, bisexual and other men who have sex with men (MSM).
• CDC adapted smallpox preparedness tools and drew on HIV prevention expertise to reach communities at risk. In a year, more than 30,000 cases were reported and more than 1 million doses of JYNNEOS vaccine given.
• Black and Hispanic people made up 33% and 31% of cases, and 87% of deaths reported through early March 2023 were among Black people. The risk of future outbreaks remains.

The outbreak

Mpox is a serious viral disease that spreads from animals and is endemic in west and central Africa. An unprecedented global outbreak was detected in May 2022. CDC activated its emergency response on May 23, 2022; the World Health Organization declared a Public Health Emergency of International Concern on July 23, and the U.S. declared a public health emergency on August 4.

• Scale: by May 10, 2023, 30,395 cases and 42 deaths were reported, in all 50 states, the District of Columbia and Puerto Rico — first linked to international travel, then spreading at home.
• Who: mostly adult MSM aged 21–55; 38% of cases were in people with HIV. Of 38 deaths reported through March 7, 2023, 33 (87%) were Black people, and 94% of those who died (where known) were immunocompromised by HIV.
• Other routes, though uncommon: close household contact (including from a caregiver), heterosexual sex and needle or scalpel injuries; three infants were born to mothers with symptoms around delivery.
• A different disease picture: this outbreak (clade IIb) often caused small, localized lesions rather than the widespread rash long seen as mpox's hallmark, and some patients had proctitis. From September 2022, clinicians sought help with severely ill, severely immunocompromised patients — especially those with advanced HIV — for whom starting antiretroviral therapy early proved important.

The U.S. mpox outbreak and CDC's response, May 2022–April 2023. Figure from the CDC report.

The response

• Testing: an FDA-approved orthopoxvirus PCR test, built for smallpox preparedness, was ready at Laboratory Response Network labs in 68 locations — 6,000 tests a week in May 2022. By early July, five commercial labs raised capacity to more than 80,000 a week; 144,209 tests had been run by April 6, 2023.
• Wastewater: CDC turned its COVID-19 wastewater network — 533 sites — to mpox. Of 20,928 samples in July 2022–April 2023, 162 sites (30%) were positive at some point, often where cases were reported; by April 2023, only 1% were.
• Genomics: CDC posted the first U.S. sequence within 3 days of diagnosis, has analyzed more than 7,000 sequences and deposited 366 whole genomes. Fewer than 1.0% carried mutations tied to tecovirimat resistance, mostly in severely immunocompromised patients on long treatment.
• Treatment: tecovirimat, previously used only for rare orthopoxvirus infections, was given to 6,932 patients under an expanded-access protocol by April 25, 2023.
• Vaccine: JYNNEOS, a third-generation smallpox vaccine approved for mpox, was first reserved for known contacts because supplies were short, then widened. An FDA authorization on August 9, 2022 for dose-sparing intradermal injection helped stretch supply: 1.2 million doses by May 2023, giving 37% of the at-risk population a first dose and 23% both doses. Unvaccinated people had 9.6 times the incidence of the fully vaccinated; effectiveness was 85.9% for 2 doses and 75.2% for 1 (70.2% in immunocompromised people), with no new safety concerns. In 2023, the Advisory Committee on Immunization Practices voted to recommend JYNNEOS for adults at risk during an outbreak.
• Communication: seven Health Alert Network notices and six clinician calls — including images of mpox rash on different skin tones — and about 50 community listening sessions, among them 26 owners of sex-on-premises venues, 16 sex workers and 28 harm reduction groups. Messages went out through dating apps and LGBTQ+ media. By August 2022, 50% of MSM surveyed said they had fewer partners and one-time encounters, as cases fell.
• Equity: vaccine projects with community groups in 22 locations gave more than 25,000 doses at HIV conferences, Pride events, festivals and in mobile vans.

Lessons

• Preparation paid off: decades of smallpox research meant a test, a surveillance network, vaccines and treatments were already in place. That work must continue for smallpox, mpox and other biothreats.
• Plan for demand: scarce vaccine had to be carefully rationed; future plans need more JYNNEOS and equitable distribution. The tecovirimat protocol's paperwork was too heavy for an outbreak and was simplified. Providers wanted easier commercial testing, which partnerships delivered within 2 months.
• Communicate with respect: working with sexual health and HIV programs and the affected communities was key, though early messages may have missed chances to explain sexual transmission risk.
• Disparities persisted: outreach narrowed but didn't close gaps in cases, severe illness and vaccination among racial and ethnic minority groups. Raising second-dose coverage and supplying vaccine to African countries where mpox is endemic remain goals.
• Not over: the outbreak waned about 5 months after the first U.S. case, and WHO ended the emergency on May 11, 2023 — yet a cluster soon appeared in Chicago, including in some vaccinated people. The link with HIV calls for combined care for HIV, sexually transmitted infections and mpox. Research continues on boosters, new treatments, animal reservoirs and new tests.

Sources

Based on Jennifer H. McQuiston, Christopher R. Braden, Michael D. Bowen and others, "The CDC Domestic Mpox Response — United States, 2022–2023," MMWR, Centers for Disease Control and Prevention; a work of the United States government in the public domain. The report's summary gives 87% of 42 deaths as among Black people; its results give 33 of 38 deaths reported through March 7, 2023, which this page follows.