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We’ve stopped vaccinating for smallpox, but now monkeypox has surfaced

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Brett W. Petersen MD MPH

Medical Epidemiologist, Poxvirus and Rabies Branch, CDC

Monkeypox is a serious viral disease that causes a pustular rash illness similar to smallpox. The disease can be fatal in up to 11% of cases, and those that survive can be left with significant complications including scars and blindness.


Monkeypox occurs regularly in parts of Central and West Africa, and there has been an increase in the number of reported cases in recent years. Many countries are detecting cases for the first time in decades. For example, Nigeria experienced the largest ever outbreak of monkeypox in West Africa in 2017 and 2018 after not having reported a case since 1978. Cases linked to Nigeria have also been found in the United Kingdom, Israel, and Singapore in 2018 and 2019.

Monkeypox cases are on the rise following smallpox eradication

It’s not totally clear why we are seeing this increase in monkeypox cases. One factor is likely the waning immunity among the human population due to the eradication of smallpox.

The vaccine for smallpox also provides protection against monkeypox because they are related viruses. Since smallpox was eradicated in 1980, there have been no routine smallpox vaccinations given to the general public, rendering anyone under the age of 39 more susceptible to contracting the disease.

Most people get monkeypox through contact with animal reservoirs of the virus (e.g. activities such as hunting, trapping, or preparing meat from rodent species such as Gambian rats, rope squirrels, or dormice, which are suspected of harbouring the virus).

Monkeypox can be airborne; good hygiene is paramount

However, the disease can also be spread person-to-person through large respiratory droplets or contact with lesion secretions. Monkeypox can be prevented by avoiding exposures to infected animals or people, isolating infected patients, practicing good hand hygiene after contact with infected animals or people, and using appropriate personal protective equipment when caring for patients.

Using smallpox vaccine with improved safety profile to tackle monkeypox

Recently, there has been renewed interest in considering the use of smallpox vaccines for the prevention of monkeypox. Many advances have been made in developing smallpox vaccines and other medical countermeasures to be used in an emergency involving smallpox. However, these same technologies can potentially be used for monkeypox as well.

CDC has collaborated with the Ministry of Health of the Democratic Republic of the Congo (DRC) and the Kinshasa School of Public Health to evaluate one such newly developed smallpox vaccine. This vaccine has been created specifically for persons at high risk of complications from traditional smallpox vaccines and has shown an improved safety profile.

1,000 participants in trial study

The goal of the vaccine study is to demonstrate that it can be administered safely to healthcare workers in areas at high risk of monkeypox and that those vaccinated develop a protective immune response.

To date, 1,000 participants have been enrolled in the study and vaccinated and are currently being monitored for monkeypox virus exposures and infections. Continued efforts to repurpose medical countermeasures for the benefit of populations afflicted with monkeypox holds great potential for reducing the suffering due to this neglected disease as well as increasing preparedness for outbreaks of monkeypox and similar diseases.

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