Does the smallpox vaccine protect against monkeypox?

Does the smallpox vaccine protect against monkeypox?

Fact-checked June 2, 2022 by Vivianna Shields, a journalist and fact-checker with experience publishing on health and wellness topics.

As cases of monkeypox continue to spread around the world, people's questions have ranged from "What is it?" to “How can I protect myself?” And as it turns out, some older people in the U.S. may still have some protection from the virus because of a previous vaccination: the smallpox vaccine.

“Smallpox vaccination also protects against monkeypox,” Hannah Newman, MPH, director of epidemiology at Lenox Hill Hospital, told Health. “People who were vaccinated against smallpox years ago may have some immunity or at least some protection against milder disease if they are infected.”

The U.S. officially stopped routine smallpox vaccination in 1972 after the disease was eradicated, but amid concerns about bioterrorism, the government has a large stockpile of smallpox vaccine - enough to vaccinate all Americans who would need protection should a future outbreak occur.

What does this all mean for the current rise in monkeypox cases? How much protection does earlier smallpox vaccination provide to older adults at risk of monkeypox? And how does the US plan to distribute these vaccines for the current outbreak? Here's what you should know.

Smallpox vaccination and monkeypox protection for children

Newman says people who received the smallpox vaccine before its discontinuation in 1972 likely still have some protection against the related monkeypox virus and other orthopoxviruses — it's just not entirely clear how much.

A 2007 study published in the journal Clinical and Vaccine Immunology found that earlier childhood smallpox vaccination does not provide complete protection against monkeypox - but it does provide partial protection. The researchers also found that among those who had previously been vaccinated against smallpox, those who still became infected with monkeypox had lower disease severity.

“Protection is clearly waning,” William Schaffner, MD, professor of medicine in the division of infectious diseases at Vanderbilt University School of Medicine, told Health. “How much, and certainly how much against monkeypox, we don’t know.”

The symptoms and causes of monkeypox as virus cases rise worldwide

Current vaccines provide protection against smallpox and monkeypox

There are two different smallpox vaccines in the United States that are either approved or may be helpful against monkeypox: ACAM2000 and Jynneos. Both were approved by the US Food and Drug Administration (FDA) - ACAM2000 in 2007 and Jynneos in 2019.

None of these vaccines were specifically used when smallpox vaccination was mandatory in the 20th century, Newman said. But ACAM2000 replaces Dryvax, which was licensed by the FDA in 1931 and uses the same type of virus to generate an immune response.

The ACAM2000 vaccine does not contain variola virus (the virus that causes smallpox), but it does contain live vaccinia virus, which belongs to the smallpox virus family and is related to variola virus. The vaccine is approved for people aged 18 and over who are at high risk for orthopoxviruses (at the moment this includes people in laboratories working with orthopoxviruses and military personnel), but can be used if necessary in people exposed to monkeypox.

The vaccine differs from typical vaccines in that it does not contain an injection. Instead, the vaccine is administered using a two-pronged (bifurcated) needle that is dipped into the vaccine solution and then inserted into the upper arm. A small, red, itchy, sore spot (known as a “pock”) appears at the vaccination site, indicating a successful vaccination. The spot then turns into a blister, then a scab, leaving a scar.

Jynneos is the newer vaccine approved in the United States to prevent monkeypox and smallpox. Like ACAM2000, Jynneos is made from the vaccinia virus, but in a modified form called “Modified Vaccinia Ankara”. It is non-replicating, meaning it cannot replicate in human cells and does not cause disease. The vaccine is intended for people aged 18 and over who are at higher risk of orthopoxvirus and is given in two doses four weeks apart.

Vaccine effectiveness and CDC recommendations

According to the CDC, the smallpox vaccine is at least 85% effective in preventing monkeypox, based on previous data from Africa. Meanwhile, Jynneos' effectiveness against monkeypox was concluded from the vaccine's immunogenicity - or its ability to elicit an immune response - and effectiveness based on animal studies.

While a large quantity of the ACAM2000 vaccine is available - more than 100 million doses - the availability of the Jynneos vaccine is significantly lower, with just over 1,000 doses currently in the supply, although this is expected to increase.

In a Morbidity and Mortality Weekly Report (MMWR) released by the CDC on May 27, the agency accepted the recommendations of the Advisory Committee on Immunization Practices to make Jynneos available to those at high risk of exposure and infection - that may include people studying monkeypox in laboratories as well as health care workers who may currently be dealing with the current outbreak.

The CDC is also beginning to mobilize the monkeypox vaccine, given the increase in cases, by focusing on those who have been directly exposed. "Right now, while we are in the early stages of investigation, we know that those at highest risk of infection are those who have had contact with a known monkeypox patient," Jennifer McQuinston, DVM, MS, a veterinarian and deputy director of the CDC's Division of Pathogens and Pathology with serious consequences, told CNN. “So those are the people we're really focused on right now to recommend vaccinations: post-exposure vaccinations.”

This strategy is also known as “ring vaccination,” in which direct contacts of confirmed monkeypox patients are vaccinated. “Currently, the vaccine is available through public health to individuals who have been in contact with confirmed or suspected cases,” Newman said. “This strategy ensures that everyone who has been or could have been exposed to a patient with smallpox receives the vaccine.”

However, the vaccines are unlikely to be widely available to the general public after that. “This is not something that everyone needs,” said Dr. Maria Van Kerkhove, head of emerging diseases and zoonoses at the World Health Organization during a Q&A on social media. “It is a virus that spreads between people who come into close contact with those who are cases.”

Other Monkeypox Prevention Strategies

Even without a nationwide vaccination effort - which again is unlikely - there are still ways to minimize the risk of contracting monkeypox.

Because the virus is spread through contact with infected animals or people or materials that have been contaminated with infected body fluids, the best prevention strategy is to avoid contact with animals, people, or materials (bedding, clothing, towels) that could harbor the virus.

And as with many other viruses, proper hygiene is important here too. This means washing hands with soap and water or using an alcohol-based hand sanitizer after possible exposure, as well as using personal protective equipment.

If you think you have been exposed to monkeypox - either through travel or close contact with an infected person - you should talk to your doctor as soon as possible and isolate yourself from others to minimize the risk of transmission.

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