ACAM2000
ACAM2000 is a live vaccine that's used to prevent smallpox and mpox. It's FDA approved for certain people who are at high risk of being exposed to these viruses. The vaccine is administered as a single dose using a special method where a healthcare professional makes a few small pricks on your skin. A small blister will form at the spot where it was given, showing that the vaccine is working. Common side effects can include redness or pain at the injection site, headache, and tiredness.
What is ACAM2000?
What is ACAM2000 used for?
How ACAM2000 works
ACAM2000 is a live vaccine that contains the vaccinia virus. This virus is related to the ones that cause smallpox and mpox but doesn't cause those conditions. The vaccine works by training your immune system to make antibodies that recognize and fight the smallpox and mpox viruses if you’re ever exposed to them.
Drug Facts
What are the side effects of ACAM2000?
Common Side Effects
- Itching at the injection site (up to 92%)
- Redness at the injection site (up to 74%)
- Pain at the injection site (up to 67%)
- Lymph node pain (up to 57%)
- Headache (up to 50%)
- Tiredness (up to 48%)
- Swelling at the injection site (up to 48%)
- Muscle pain (up to 46%)
- Feeling unwell (up to 37%)
- Feeling hot (up to 32%)
Other Side Effects
- Shivering
- Nausea
- Diarrhea
- Constipation
- Vomiting
- Rash
- Shortness of breath
- Rash
- Swollen lymph nodes
Serious Side Effects
- Heart inflammation: chest pain, shortness of breath, fast heartbeat, fainting, irritability, no energy, vomiting, stomach pain, pale skin
- Brain and spinal cord inflammation: confusion, headache, nausea, vomiting, weakness, unstable balance and coordination, numbness or tingling, loss of consciousness, seizures
- Serious skin reactions: painful rash, blisters, itching, swelling, fever
- Eye infection: watery painful eyes, blurred vision, blindness
- Severe allergic reaction: facial or throat swelling, trouble breathing, hives, itching
Source: DailyMed
The following side effects have also been reported
Side effects that you should report to your care team as soon as possible:
- Allergic reactions—skin rash, itching, hives, swelling of the face, lips, tongue, or throat
- Dizziness, loss of balance or coordination, confusion or trouble speaking
- Eye pain, redness, irritation, or discharge with blurry or decreased vision
- Heart muscle inflammation—unusual weakness or fatigue, shortness of breath, chest pain, fast or irregular heartbeat, dizziness, swelling of the ankles, feet, or hands
- Redness, blistering, peeling, or loosening of the skin, including inside the mouth
- Skin infection—skin redness, swelling, warmth, or pain
Side effects that usually do not require medical attention (report these to your care team if they continue or are bothersome):
- Fever
- General discomfort and fatigue
- Headache
- Muscle pain
- Nausea
- Pain, redness, or irritation at injection site
- Swollen lymph nodes in the neck, groin, chest, or underarm area
Pros and cons of ACAM2000
Pros
Protects against both smallpox and mpox
Not a routine vaccine that everyone needs to get
Only one dose is needed to complete vaccination
Cons
Given as multiple pricks into the skin
Risk of serious side effects, including heart and skin problems
Requires careful aftercare to prevent the virus from spreading
Pharmacist tips for ACAM2000
ACAM2000 is given using a needle that's first dipped into the vaccine and then pricked into the skin of your upper arm several times in a few seconds.
ACAM2000 can leave a scar. After getting the vaccine, you’ll likely develop a red, itchy sore in 2 to 5 days that turns into a blister. The blister might drain, then scab over and fall off after about 3 weeks, leaving a small scar.
ACAM2000 can interfere with certain tests, like syphilis and TB skin test. Tell your care team that you’ve received this vaccine. TB skin tests should be delayed for at least 6 weeks after vaccination.
If you have a severe reaction to ACAM2000, you or your prescriber should report it to the Vaccine Adverse Event Reporting System (VAERS).
After vaccination care:
After getting ACAM2000, follow special care instructions to care for the vaccination site. These steps will make sure it heals properly and prevents spreading the vaccine virus to others.
The live virus from ACAM2000 can spread to others through close contact. Avoid contact with people at high risk of infection, such as those with eczema, weakened immune systems, pregnant people, or babies under 12 months old.
Keep the area where you received ACAM2000 loosely covered, clean, and dry. If the bandage gets wet, change it right away, and use a waterproof cover when bathing.
Change your bandage every 1 to 3 days, but sooner if it gets dirty or wet. Seal used bandages in a plastic zip-top bag before throwing them in the regular trash.
Always wear clothing with sleeves that cover the vaccination site. Try not to touch the area with your bare hands, and use gloves when changing bandages. If you touch it accidentally, wash your hands right away.
Do your own laundry and keep your clothes separate from other people’s clothing, both in hampers and in the washer and dryer. Don’t share towels or washcloths with others.
When the scab from ACAM2000 falls off, place it in a plastic zip-top bag and throw it away, then wash your hands thoroughly.
Frequently asked questions about ACAM2000
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What are the risks and warnings for ACAM2000?
ACAM2000 can cause some serious health issues. This risk may be even higher for certain groups. If this worries you, talk to your doctor or pharmacist about other options.
Serious health problems
Risk factors: Heart problems | Weakened immune system | Currently pregnant | Children under 12 months old
Most people who get ACAM2000 only have mild side effects. But in rare cases, serious health problems can happen, especially if it’s your first time receiving it. These problems can happen after the first dose or a later (booster) dose. Some serious reactions and their symptoms include:
Heart inflammation: chest pain, shortness of breath, fast heartbeat, fainting, irritability, no energy, vomiting, stomach pain, pale skin
Brain and spinal cord inflammation: confusion, headache, nausea, vomiting, weakness, unstable balance and coordination, numbness or tingling, loss of consciousness, seizures
Skin problems: painful rash, blisters, itching, swelling, fever
Eye problems: watery painful eyes, blurred vision, blindness
If you notice any of these symptoms, get medical help right away and contact your prescriber so they can manage your care.
Heart problems
Risk factors: History of heart conditions | High blood pressure | High cholesterol | Diabetes | Family history of early heart problems| Smoke cigarettes
ACAM2000 has been linked to rare cases of heart inflammation and other serious heart problems, including heart attack and heart failure, though it's unclear if the vaccine directly causes them. Your risk is higher if you already have heart problems or risk factors like high blood pressure, high cholesterol, diabetes, a family history of heart problems, or if you smoke cigarettes. Tell your prescriber about any heart conditions or risk factors before getting this vaccine so they can decide if it’s safe for you.
Eye infections
Risk factors: Also using corticosteroid eye drops
If the ACAM2000 vaccine virus accidentally gets into your eye, it can cause a serious infection. This can lead to eye problems such as inflammation, scarring of the cornea, or even vision loss. Your risk is higher if you use corticosteroid eye drops. Let your prescriber know if you experience watery painful eyes, blurred vision, or blindness. Be careful not to touch your vaccination site and then your eyes, and wash your hands well after changing bandages.
Severe skin reactions
Risk factors: History of eczema or other skin conditions
If you have eczema or another skin condition that causes rashes or irritation, you might be at higher risk for a serious reaction called eczema vaccinatum after getting ACAM2000. This risk can still exist even if your eczema isn’t active or happened a long time ago. Because the vaccine contains a live virus that can spread from the injection site, people you live with who have eczema or other skin problems could also be at risk for this reaction. Tell your prescriber if you or anyone you live with has a skin condition before getting this vaccine.
Harm to unborn baby
A study found that serious harm from ACAM2000 is rare, but if it does happen, it can be life-threatening to an unborn baby. If you receive this vaccine while pregnant or within 6 weeks before becoming pregnant, there might be risks to your baby. You should avoid becoming pregnant for at least 6 weeks after getting the vaccine and until the vaccination site has fully healed.
If you’re pregnant and live with someone who recently received ACAM2000, there’s also a small risk the vaccine virus could spread to you through close contact. Talk with your prescriber right away if you’re pregnant or planning to become pregnant and have questions about these risks.
Severe allergic reactions
Risk factors: Allergy to neomycin or polymyxin B
There's a small chance that you might have a severe allergic reaction, like anaphylaxis, to ACAM2000. Get medical help right away if you notice symptoms like feeling faint, swelling of the face, closing of the throat, difficulty breathing, hives or rash, dizziness, shaking, nausea, or chest pain.
Prevent spreading the vaccine virus
The best way to prevent spreading the vaccine virus from ACAM2000 is to wash your hands thoroughly after touching the vaccination site or changing your bandage. Use soap and warm water or an alcohol-based sanitizer every time.
Avoid close contact with people who could have serious reactions to the vaccine virus, including those with heart or eye problems, weakened immune systems, eczema, pregnant people, or babies under 12 months old.
To reduce fluid buildup under your bandage, first cover the site with dry gauze, then apply the dressing over it. Change the gauze and dressing every 1 to 3 days, or sooner if they get wet or dirty.
Delay blood and organ donation
You shouldn't donate blood or organs for 6 weeks after getting ACAM2000.
ACAM2000 dosage forms
Typical dosing for ACAM2000
The typical dose is one drop of the vaccine placed on the skin of your upper arm or shoulder. Your healthcare professional will then use a special needle to make about 15 quick pricks through the vaccine drop, causing a small drop of blood to show it was given correctly.
ACAM2000 contraindications
People with very weak immune systems
What are alternatives to ACAM2000?
Prevention of smallpox and monkeypox in adults
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References
Best studies we foundAmerican Academy of Dermatology Association. (n.d.). Smallpox vaccine: What are the risks if someone has eczema?
Badell, M. L., et al. (2015). Risks associated with smallpox vaccination in pregnancy: A systematic review and meta-analysis. Obstetrics and Gynecology.
Centers for Disease Control and Prevention. (2024). Getting Your Smallpox Vaccine.
Centers for Disease Control and Prevention. (2024). Smallpox Vaccine.
Emergent Product Development Gaithersburg Inc. (2025). ACAM2000 (smallpox- vaccinia vaccine, live injection, powder, lyophilized, for solution [package insert]. DailyMed.
Food and Drug Administration. (2024). FDA Roundup: August 30, 2024.
Myocarditis Foundation. (n.d.). Understanding the Difference Between Myocarditis, Pericarditis, and Myopericarditis.
Petersen, B. W., et al. (2016). Use of Vaccinia Virus Smallpox Vaccine in Laboratory and Health Care Personnel at Risk for Occupational Exposure to Orthopoxviruses — Recommendations of the Advisory Committee on Immunization Practices (ACIP), 2015. Morbidity and Mortality Weekly Report.
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