That scar you have on your arm is probably from a BCG vaccine – not a smallpox vaccine that could protect from monkeypox

By Stephanie Nguyen, MS ('22)

Stephanie Nguyen headshotBorn in Vietnam, I was left with a permanent scar on my left arm. This little scar may be familiar to many immigrants, who often have one on the top or underside of their arms.

But is this a smallpox vaccine, and, if so, will it protect me against monkeypox?

The Centers for Disease Control and Prevention (CDC) has recommended that health departments consider using ACAM2000, an FDA-approved vaccine used against smallpox, to help control monkeypox. The previous smallpox vaccine, once a part of the routine childhood vaccination series in the United States, left a scar similar to the one I have. This has led many foreign-born persons to conclude that they have already received this vaccine.

But many, like me, have not.

Many foreign-born persons have received the bacille Calmette-Guerin (BCG) vaccine for TB disease. This vaccine is administered at birth in many countries outside of the U.S. to prevent childhood tuberculous meningitis and miliary disease. BCG leaves a scar like the smallpox vaccine. But it doesn’t protect against smallpox.

In the social media post that caught my attention and drove me to write this post, an individual shared how their parents have received the smallpox vaccine and showed their scars. Another younger individual then extrapolated from that information that their scar was from a smallpox vaccine, rather than the BCG, and relayed this false information to their followers. Although the initial post was likely correct that the poster’s parents had received the smallpox vaccine, the information extrapolated and shared by the younger user was no longer correct.

It’s highly unlikely that anyone under the age of 42 has received a smallpox vaccine. Smallpox was eradicated in 1979. The last smallpox vaccine was administered in the U.S. in 1972. The World Health Organization (WHO) declared smallpox eliminated around the world in 1980 and stopped administering or promoting the smallpox vaccine. This means that any individuals under the age of 42 certainly did not receive the smallpox vaccine as a child.

Even those who are old enough to have a smallpox vaccine scar shouldn't rely on that vaccine to remain active enough to protect them from monkeypox now. According the CDC, the smallpox vaccine provides full immunity for 3 to 5 years

With this, please be cautious of what you read and see on social media. On many platforms, false information often circulates faster than scientifically accurate information. And even if the information is technically correct, it can be extrapolated without the appropriate scientific nuances.

Please utilize primary sources of information like the CDC or the WHO as your primary sources. And always please consult with your primary care physician or local health authorities about how to prevent monkeypox or any other disease for which you may be at risk.