Editorial by: MICHAEL T. OSTERHOLM AND BRUCE GELLIN
SCIENCE 19 Jul 2022. Vol 377, Issue 6604, p. 349
Dr. Michael Osterholm Photo Credit: University of Minnesota profile
DOI: 10.1126/science.add9651
The World Health Organization (WHO) hasn’t called the current monkeypox outbreak a Public Health Emergency of International Concern (PHEIC), but as a worldwide epidemic, it is clearly an emerging pandemic. More than 12,556 monkeypox cases and three deaths have been reported in 68 countries since early May, and these numbers will rise rapidly with improved surveillance, access to diagnostics, and continuing global spread of infection. Although many tools are needed to control this unfolding pandemic, it’s clear that limiting ongoing spread will require a comprehensive international vaccination strategy and adequate supplies.
People 40 years old and younger who have not benefitted from the immunization campaign that eradicated smallpox by 1980 are now susceptible to monkeypox (which is in the same virus family as smallpox), and this lack of population immunity has contributed to the current outbreak. Most of the cases to date have occurred among men who have sex with men (MSM), particularly those with new or multiple partners. Epidemiologic investigations indicate that the predominant mode of transmission is through skin-to-skin and sexual contact, not contact with contaminated clothing or bed linens. Although respiratory droplet transmission might occur, there is no evidence of airborne transmission as there is with COVID-19. And because monkeypox is a self-limited infection with symptoms lasting 2 to 4 weeks, there isn’t a chronic carrier state as there is with HIV, which would increase the risk for ongoing transmission.
Although many tools are needed, it is clear that limiting ongoing spread will require widely available vaccination. The ACAM2000 vaccine is licensed by the US Food and Drug Administration for smallpox and allowed for use against monkeypox on an expanded access basis (so-called “compassionate use” for an investigational drug use). It is associated with potentially serious side effects. A newer vaccine with an improved safety profile was approved for monkeypox and smallpox in 2019. This two-dose vaccine, produced by Bavarian Nordic, is a modified vaccinia virus Ankara (MVA; Jynneos in the United States, Imvanex in the European Union, and Imamune in Canada). Its supply, however, is limited.
How can the world leverage these vaccines to control the spread of monkeypox? Transmission among MSM populations must be reduced through aggressive public health measures, including increased vaccination and diagnostic testing and extensive education campaigns targeted at populations at risk and minimizing social stigma. In addition to a massive scaling up of vaccine production, other immediate dose-sparing actions can be taken: administration of a single dose per person instead of two doses (or a first dose followed by a delayed second dose when supplies allow) or intradermal (versus intramuscular) administration of a smaller dose. However, research will be needed to determine whether such dose-sparing approaches provide adequate immune protection.
Determining how vaccine will be allocated to countries and within countries to have the most impact on transmission is essential. Expect major shortages of vaccine among frustrated at-risk individuals for many months to come. To dampen the current outbreak will require vaccination of those at highest risk, with global estimates of the number of MSM ranging from 1 to 3%. The needed global vaccine supply just for MSM is similar to those considered for HIV oral preexposure prophylaxis (PrEP). It is estimated that by 2023, 2.4 million to 5.3 million people worldwide should receive PrEP.
Monkeypox is a zoonotic disease; thus, another critical step is to greatly reduce transmission of the virus from current rodent reservoirs and to prevent spillovers in areas of the world where monkeypox isn’t endemic. Long-term control of monkeypox will require vaccinating as many as possible of the 327 million people 40 years of age and younger living in the 11 African countries where monkeypox is endemic in an animal (rodent) reservoir. This effort should include childhood vaccine programs. Surveillance will be needed to identify new animal reservoirs, which might be established in other countries as a result of infected humans inadvertently transmitting the virus to domestic rodents that have subsequent contact with wild rodents.
The smallpox eradication program was a 12-year effort that involved 73 countries working with as many as 150,000 national staff. Because of its animal reservoir, monkeypox can’t be eradicated. Unless the world develops and executes an international plan to contain the current outbreak, it will be yet another emerging infectious disease that we will regret not containing.