Does Childhood Smallpox Vaccine Protect Against Monkeypox?

From the early 1800s through 1972, Americans were vaccinated against the smallpox virus. Suppose you received your childhood vaccine or a booster vaccine in the military. Do you have immunity against monkeypox, the newest global infectious disease threat?

Key takeaways:
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    Smallpox vaccination provides 85% protection against monkeypox.
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    Vaccination protection depends on the duration immunity lasts, which is unknown.
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    Those unvaccinated for smallpox are naïve to poxviruses.
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    To prevent any infectious disease, practicing proper hygiene remains critical.

Monkeypox vs. smallpox

What is this poxvirus causing global public health concerns? Monkeypox, an infectious disease most commonly transmitted from animals to people, is the culprit.

Science recognizes similarities between monkeypox and the once-common but more deadly smallpox virus.

Smallpox was eliminated in the U.S. in 1972 and globally in 1980. The removal of naturally occurring smallpox virus occurred because no animal reservoir harboring the virus exists in nature; it was solely a human disease. This fact and a successful vaccination program helped eradicate this dreadful illness.

Monkeypox specifics

Monkeypox can affect many species. Generally, it goes from animals to people, though reverse transmission (reverse zoonosis) may be possible.

Disease spread occurs by:

  • Close contact, including sexual activity.
  • Skin-to-skin contact with infected animals or people.
  • Rubbing up against items like contaminated clothing.
  • Exposure to respiratory droplets, though it’s much less contagious than COVID-19 or the flu from this route.

Monkeypox can cause various signs and may start one to two weeks after exposure. Symptoms may include:

  • Fever.
  • Muscle aches.
  • Headache.
  • Weakness.
  • Exhaustion.
  • Big lymph nodes (lymphadenopathy), which doesn't occur in smallpox, helping to set them apart.

After these initial signs, a rash begins that proceeds through four stages before scabbing over and healing.

Most people recover without any treatment within two to four weeks. But those with a weakened immune system, are pregnant, or children may have a higher risk for serious disease or complications. Vaccination before or after a recent exposure may help protect those at higher risk and those around them.

Will my smallpox vaccine protect me?

Were you born before 1972? Did you receive the smallpox vaccine? If so, you may wonder if you are protected, as smallpox and monkeypox viruses are related, and have similar symptoms.

For those who received the smallpox vaccine as children or for military or professional research-related activities, it isn't exactly known how long immunity will last. According to the Centers for Disease Control and Prevention (CDC), theoretically, the vaccine provides about 85% cross-protection against the monkeypox virus. However, that doesn't account for how long ago you may have received the vaccine, or other factors.

Smallpox vaccine – did I receive it?

Do you have a circular scar, also referred to as a “lake”, on one arm, like the picture here? If so, then you likely received the smallpox vaccine.

Smallpox vaccine scar
Image by Shutterstock

However, not all people vaccinated developed that lovely reminder. So, you may have been vaccinated and not know it or cannot outwardly prove it.

If you were vaccinated but didn't develop the telltale lake sign, does that mean you have no immunity? Scientists aren't quite sure. But in a study by Han et. al., findings suggest that those vaccinated, even those without the scar, did develop an immune response and would likely have protection, but to what degree remains unknown.

Smallpox vaccine against monkeypox

Some scientists suggest that the increase in monkeypox globally is due to the lack of immunity by millions of people, either because they never received the smallpox vaccine or because those vaccinated have minimal remaining protection.

Think about it, everyone in the U.S. under 50 years old never received a smallpox vaccine. So, monkeypox is novel to their immune system.

But if you were vaccinated, will your smallpox vaccine protect you? The simple answer is: maybe!

Monkeypox vaccines

Today, while smallpox doesn't exist naturally, it still does in research facilities. So, a small stockpile of vaccines exists for researchers and in case of accidental virus release. However, since Monkeypox started popping up outside of Africa, where it naturally resides, monkeypox-specific vaccinations have been developed.

How to stay safe from monkeypox

Even if you were vaccinated with the smallpox vaccine, prevention is key. Protective measures, regardless of if you had a vaccine, remain essential. Always practice proper hygiene. This holds true for any contagious disease and includes:

  • Washing your hands regularly or using > 60% alcohol content sanitizer.
  • Avoid close contact with anyone with a known rash that could be monkeypox.
  • Do not touch rashes, hug, kiss, or have sexual relations with known infected people.
  • Do not share things like cups, food, bedding, or clothing of infected people.

Regardless of your smallpox vaccination status, take steps to protect yourself and those around you. In the COVID-19 era, we are seeing just how far and wide diseases can spread and that multiple strategies are needed to protect others and ourselves.


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