Smallpox Vaccine Scar

What is a smallpox vaccine scar?

A smallpox vaccine scar is a small mark you may have on your arm if you’ve received a vaccine that protects you against smallpox. The scar is generally round but may have irregular edges. It may also be a little bit lower than the surrounding skin.

Specific vaccines that cause this scar include:

• ACAM2000™. ACAM2000 is the vaccine healthcare providers currently use to protect people from smallpox. They give it to laboratory workers who work with certain viruses and some people in the military. Most people don’t need a smallpox vaccine anymore because earlier vaccination efforts eradicated the virus that causes it. So, it’s no longer spreading anywhere in the world.
• Dryvax®. This is the smallpox vaccine providers used before the U.S. Food and Drug Administration (FDA) approved ACAM2000. Many people in the U.S. received this vaccine as part of vaccination efforts in the mid-1900s. Routine vaccination ended in 1972. After that point, only select groups of people received the Dryvax vaccine, including healthcare workers and military personnel. In 2008, providers stopped using Dryvax and replaced it with ACAM2000.

Why does the smallpox vaccine leave a scar?

The smallpox vaccine leaves a scar because it causes a minor infection in your skin. Your body fights off the infection, but this process leaves behind a small mark on your skin where the infection (and related inflammation) took place.

The ACAM2000 vaccine (and Dryvax before it) uses a two-pronged needle to cause a small, controlled infection in your skin. Your provider dips the needle in vaccine solution and pricks your skin with it multiple times. This occurs on just a small area of your upper arm.

This method causes a minor infection to form at the site. Providers call this a localized infection, meaning it’s just in that area of your skin. It’s a normal, expected result of the vaccine. The infection spurs your immune system to build up its defenses.

In case you’re wondering: the vaccine doesn’t cause a smallpox infection. It doesn’t use the virus that causes smallpox (variola virus). Instead, it uses the vaccinia virus. Vaccinia is related to variola, so when your body builds immunity against vaccinia, it’s also prepared to ward off variola.

Within three to four days, a red, raised and itchy spot develops at the vaccination site. This is a sign of “a take,” which means the vaccine is doing its job. This spot soon turns into a pus-filled blister that gradually gets a little bigger by day 10. Then, it slowly starts to dry out. As the blister heals, a scab develops. This is a normal part of your skin’s healing process. By 14 to 21 days after vaccination, the scab falls off. In its place, a small, pitted scar remains.

This scar is a sign that the vaccine worked. It gave you immunity against smallpox, as it’s designed to do. But keep in mind that full immunity isn’t lifelong. Research shows immunity starts to lessen about three to five years after vaccination. This is why certain people (like lab workers) might need repeated vaccination over many years to stay fully protected.

Why don’t I have a smallpox vaccine scar?

If you received a smallpox vaccine recently but don’t have a scar, it’s possible the vaccine didn’t “take.” But this is an issue a healthcare provider will typically catch earlier in the process (before you’d notice the lack of a scar).

Providers look for signs of “a take” within the first week or so after vaccination. They check to make sure a blister is forming, which is a sign your body is responding as it should. If these signs aren’t present, you may need a repeat vaccination. Your provider will advise you on what’s best in your situation.

People who received a smallpox vaccine years ago may still have their scars. Or, they may fade slightly over time. Some people choose to get scar revision to reduce the appearance of their scar.

Does the mpox vaccine cause a scar?

It depends on which vaccine you receive. The viruses that cause smallpox and mpox are closely related. So, this allows healthcare providers to use smallpox vaccines to protect people from mpox. People who receive ACAM2000 will develop a vaccine scar. But healthcare providers in the U.S. prefer to use the JYNNEOS® vaccine to protect people against mpox. It has a lower risk of serious side effects.

People who receive JYNNEOS may develop a scar, depending on the method of vaccination. There are two different methods for giving you the JYNNEOS vaccine:

• Intradermal vaccination: You typically receive this type of shot in the inner side of your forearm. Your provider uses a small needle to inject the vaccine between the top two layers of your skin (epidermis and dermis). Your skin contains lots of immune cells. So, just a small dose of the vaccine can easily stimulate those cells and help your body build its defenses. When there’s a sudden outbreak of a condition like mpox, using smaller doses allows more people to get vaccinated.
• Subcutaneous vaccination: You usually receive this type of shot in your upper arm. Your provider uses a needle to inject the vaccine into the deepest layer of your skin (hypodermis).

Both methods are safe and effective. Intradermal vaccination may lead to skin irritation and discoloration. These skin changes are usually temporary. But in some people, the vaccine leads to long-term scarring. People at greater risk include those who:

• Have a history of severe scarring.
• Have a history of keloid scars. These are thick scars that raise above the surface of your skin. They may be red or pink. Or, they may look the same or darker than your natural skin tone.

People who have darker skin have a higher risk of developing keloid scars. These include people who are Black, Latino or Asian.

Anyone at risk for scarring shouldn’t receive the intradermal vaccination. Instead, they should receive the subcutaneous vaccination. Your healthcare provider will talk to you about your medical history (including any history of scarring) before giving you the shot. They’ll make sure to use the method that’s suitable for you.

Does a smallpox vaccine scar mean you have immunity against mpox?

Your healthcare provider is the best person to tell you if you have immunity against mpox or any other infectious disease. That’s because many factors can affect your level of protection, including:

• Which vaccine you received (for example, ACAM2000 or JYNNEOS).
• When you received it.
• How long that specific vaccine provides protection.

Your provider can assess your immunity according to your vaccine history and the latest research on the vaccine’s durability.

Keep in mind that just because you have a mark on your arm that looks like a smallpox scar doesn’t mean you received a smallpox vaccine. Some people born outside the U.S. may have received the Bacille Calmette-Guérin (BCG) vaccine against tuberculosis. This vaccine leaves a scar on a person’s arm that resembles a smallpox vaccine scar.

However, these are two very different vaccines that protect against different viruses. You’re not protected against mpox unless you receive a vaccine designed and approved for that purpose.

A note from Cleveland Clinic

Most people with smallpox vaccine scars can remember the exact moment when they got their shot. For some, it was decades ago as part of widespread vaccination efforts to rid the world of smallpox. For others, it was more recent and necessary due to their lines of work.

Whatever the time, place or reason, the scar is a sign that your body built up its immune defenses to keep you and others safe. If you have questions about your vaccine scar or any of the vaccines you should receive, don’t hesitate to reach out to a healthcare provider.