Monday, May 15, 2023

CDC HAN: Potential Risk for New Mpox Cases


Last September, in a blog called CDC EID Journal: Monkeypox in Patient Immunized with ACAM2000 Smallpox Vaccine During 2022 Outbreak, I opened with the following paragraph. 

Although it has been often stated by public health officials (and the vaccine manufacturers), it bears repeating; we really don't know how effective the JYNNEOS(TM) vaccine approved in 2019 (and the older ACAM2000 smallpox vaccine) will be against the strain of Monkeypox currently spreading globally.

This from the CDC website at that time:

Vaccine Effectiveness

Because Monkeypox virus is closely related to the virus that causes smallpox, the smallpox vaccine can protect people from getting monkeypox. Past data from Africa suggests that the smallpox vaccine is at least 85% effective in preventing monkeypox. The effectiveness of JYNNEOS(TM) against monkeypox was concluded from a clinical study on the immunogenicity of JYNNEOS and efficacy data from animal studies.

Smallpox and monkeypox vaccines are effective at protecting people against monkeypox when given before exposure to monkeypox. Experts also believe that vaccination after a monkeypox exposure may help prevent the disease or make it less severe. 

Today, via a CDC HAN Health Update, we're learning that the vaccine may not be as effective as originally hoped.  This HAN alert from 

RESURGENCE OF MPOX - Provider Update: May 9, 2023
Publish Date:05/09/2023 06:33:11 pm
Alert Id:46678186
Level of Alert:


RESURGENCE OF MPOX - Provider Update: May 9, 2023

Full Details

Summary and Action Items

  • Chicago Department of Public Health (CDPH) has identified a resurgence of cases of mpox (formerly monkeypox). 
  • From April 17th-May 5th 2023, 12 confirmed and one probable case of mpox were reported to CDPH. All cases were among symptomatic men. Nine (69%) of 13 cases were among men who were fully vaccinated for mpox.
  • Transmission of mpox continues locally and disproportionately affects the same populations affected by Sexually Transmitted Infections (STIs) and human immunodeficiency virus (HIV).
  • Healthcare providers are urged to remain diligent in screening and vaccinating at risk populations.
  • Vaccination is an important tool in stopping the spread of mpox, although vaccine-induced immunity is not complete. People who are vaccinated should continue to avoid close, skin-to-skin contact with someone who has mpox. 
  • JYNNEOS is a 2-dose vaccine approved for the prevention of mpox and smallpox. All eligible Chicagoans should receive both doses of the vaccine for the best protection against mpox. The second dose should be given 4 weeks after the first dose. If more than 35 days has elapsed since the first dose was given, administer the second dose as soon as possible. Vaccine boosters are not recommended at this time. 
  • CDPH encourages healthcare providers to adopt a syndemic approach to addressing mpox and including incorporating mpox, STI and HIV screening, treatment and prevention into existing sexual health services.
  • Please see the attached for more information.

Today the CDC has issued a HAN Health Update for clinicians, advising them that while vaccination is still strongly recommended (it likely still prevents some cases, and may reduce the severity of breakthrough infection), they should expect to see new cases even among previously vaccinated individuals.

Potential Risk for New Mpox Cases

Distributed via the CDC Health Alert Network

May 15, 2023, 9:00 AM ET


In the United States, cases of mpox (formerly monkeypox) have declined since peaking in August 2022, but the outbreak is not over. The Centers for Disease Control and Prevention (CDC) continues to receive reports of cases that reflect ongoing community transmission in the United States and internationally. This week, CDC and local partners are investigating a cluster of mpox cases in the Chicago area. From April 17 to May 5, 2023, a total of 12 confirmed and one probable case of mpoxwere reported to the Chicago Department of Public Health. All cases were among symptomatic men. None of the patients have been hospitalized. Nine (69%) of 13 cases were among men who had received 2 JYNNEOS vaccine doses. Confirmed cases were in 9 (69%) non-Hispanic White men, 2 (15%) non-Hispanic Black men, and 2 (15%) Asian men. The median age was 34 years (range 24–46 years). Travel history was available for 9 cases; 4 recently traveled (New York City, New Orleans, and Mexico).

Although vaccine-induced immunity is not complete, vaccination continues to be one of the most important prevention measures. CDC expects new cases among previously vaccinated people to occur, but people who have completed their two-dose JYNNEOS vaccine series may experience less severe symptoms than those who have not.

Spring and summer season in 2023 could lead to a resurgence of mpox as people gather for festivals and other events. The purpose of this Health Alert Network (HAN) Health Update is to inform clinicians and public health agencies about the potential for new clusters or outbreaks of mpox cases and to provide resources on clinical evaluation, treatment, vaccination, and testing.


A global outbreak of mpox began in May 2022. Previous outbreaks in places where mpox is not endemic were mostly related to international travel; however, this outbreak spread rapidly across much of the world through person-to-person contact, disproportionately affecting gay and bisexual men, other men who have sex with men (MSM), and transgender people. Most patients with mpox have mild disease, although some, particularly those with advanced or untreated HIV infection, may experience more severe outcomes.

As of May 10, a total of 30,395 cases have been reported in the United States. This outbreak had a peak of about 460 cases per day in August 2022, and gradually declined, likely because of a combination of temporary changes in sexual behavior, vaccination, and infection-induced immunity[1,2]. However, CDC continues to receive reports of new cases and clusters in the United States and internationally.

Although approximately 1.2 million JYNNEOS mpox vaccine doses have been administered in the United States since the beginning of the outbreak, only 23% of the estimated population at risk for mpox has been fully vaccinated. Vaccine coverage varies widely among jurisdictions. The projected risk of a resurgent mpox outbreak is greater than 35% in most jurisdictions in the United States without additional vaccination or adapting sexual behavior to prevent the spread of mpox [3]. Resurgent outbreaks in these communities could be as large or larger than in 2022.

To help prevent a renewed outbreak during the spring and summer months, CDC is urging clinicians to be on alert for new cases of mpox and to encourage vaccination for people at risk. If mpox is suspected, test even if the patient was previously vaccinated or had mpox. Clinicians should also refamiliarize themselves with mpox symptomsspecimen collectionlaboratory testing procedures, and treatment options.      

Like all viruses, Mpox continues to evolve and diversify, as discussed in the 2014 EID Journal article Genomic Variability of Monkeypox Virus among Humans, Democratic Republic of the Congo, where the authors cautioned:
Small genetic changes could favor adaptation to a human host, and this potential is greatest for pathogens with moderate transmission rates (such as MPXV) (40). The ability to spread rapidly and efficiently from human to human could enhance spread by travelers to new regions.
In a 2020 report, published by the Bulletin of the World Health Organization, researchers warned that our waning immunity to smallpox put society at greater risks of seeing Monkeypox epidemics (see WHO: Modelling Human-to-Human Transmission of Monkeypox). 

While Mpox is currently disproportionately affecting gay, bisexual, and other men who have sex with men (MSM), there are no guarantees that pattern won't change over time. 

Since the eradication of smallpox in the 1970s, there is a general feeling that poxviruses are a thing of the past, a relic of the 20th century. But viruses have been around far longer than humans, and nature is nothing if not persistent, making it unwise to bet against their long-term success.