Yes, smallpox vaccines offer protection against monkeypox

The World Health Organization (WHO) recently declared the multi-country monkeypox outbreak a global public health emergency.

This comes as tens of thousands of cases have been reported in more than 70 countries, with several thousand of those cases in the U.S.

As cases have increased worldwide, some people are searching for ways to prevent infection. Claims on social media say that smallpox vaccines offer protection against monkeypox infection.

THE QUESTION

Do smallpox vaccines offer protection against monkeypox infection?

THE SOURCES

• Centers for Disease Control and Prevention (CDC)
• World Health Organization (WHO)
• U.S. Food and Drug Administration (FDA)
• U.S. Department of Health and Human Services (HHS)
• Stuart Ray, M.D., professor of medicine in the infectious disease division at Johns Hopkins School of Medicine

THE ANSWER

Yes, smallpox vaccines offer protection against monkeypox infection.

WHAT WE FOUND

Since monkeypox is “closely related” to the virus that causes smallpox, smallpox vaccines “can protect people from getting monkeypox,” according to the Centers for Disease Control and Prevention (CDC).

Data from past studies show that the smallpox vaccine is about 85% effective in preventing monkeypox when given before someone is exposed to the virus, the World Health Organization (WHO) and CDC say. The vaccine can also be effective at preventing illness or reducing symptom severity if it is given shortly after someone is exposed to monkeypox. 

The U.S. Food and Drug Administration (FDA) has licensed two vaccines to prevent smallpox: ACAM2000 and JYNNEOS. 

The ACAM2000 vaccine is approved by the FDA for use in smallpox prevention, but the CDC has expanded access to allow its use for monkeypox as well, according to the U.S. Department of Health and Human Services. 

The JYNNEOS vaccine was approved by the FDA in September 2019 for use in the prevention of both smallpox and monkeypox disease. People with inflammatory skin conditions such as eczema, as well as those with weakened immune systems, should only use the JYNNEOS vaccine, the CDC says. 

President Joe Biden’s administration has ramped up distribution of both vaccines, but they aren’t readily available to everyone. The vaccines are limited right now to those who are most at risk of being infected with monkeypox, including people with who were exposed to someone who has monkeypox, people who have had multiple or anonymous sexual partners, and men who have sex with men. 

Local and state health departments are determining vaccine eligibility during the current outbreak, so requirements may vary based on where a person lives. People who have questions about their eligibility should contact their local health department. 

RELATED: No, the monkeypox outbreak has not been declared a pandemic

Routine smallpox vaccinations used to be commonplace in the United States, but this practice stopped in 1972 after the disease was eradicated in the country, the CDC says. That means smallpox vaccines aren’t available to the general public anymore. Those who have previously been vaccinated against smallpox can usually find evidence as a scar on their upper arm, according to the WHO. 

So what does a previous smallpox vaccination mean during the current monkeypox outbreak?

Though previous vaccination provides protection against monkeypox, it may not be lifelong, according to the CDC. During the 2003 monkeypox outbreak and the current outbreak, some people who had received the smallpox vaccine decades ago were infected with monkeypox. 

Stuart Ray, M.D., a professor at Johns Hopkins Medicine, agrees.

“What we don't know is whether or at what point people who have had decades since that [smallpox] vaccination, or have become immunosuppressed since that vaccination, might become susceptible,” he said. 

RELATED: No, monkeypox is not considered a sexually transmitted disease