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ACAM2000 Side Effects

Generic name: smallpox vaccine

Medically reviewed by Last updated on Oct 7, 2023.

Note: This document contains side effect information about smallpox vaccine. Some dosage forms listed on this page may not apply to the brand name ACAM2000.

Applies to smallpox vaccine: injection powder for solution.


Injection route (Powder for Solution)

Myocarditis, pericarditis, encephalitis, encephalomyelitis, encephalopathy, progressive vaccinia, generalized vaccinia, severe vaccinial skin infections, erythema multiforme major (including Stevens-Johnson syndrome), eczema vaccinatum resulting in permanent sequelae or death, ocular complications and blindness and fetal death, have occurred following primary vaccination or revaccination. Certain individuals are at an increased risk which may lead to severe disability, permanent neurological sequelae and/or death.

Serious side effects of ACAM2000

Along with its needed effects, smallpox vaccine (the active ingredient contained in ACAM2000) may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor immediately if any of the following side effects occur while taking smallpox vaccine:

More common

Less common

Other side effects of ACAM2000

Some side effects of smallpox vaccine may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects.

Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:

More common

For Healthcare Professionals

Applies to smallpox vaccine: percutaneous powder for injection.


Very common (10% or more): Injection site pruritus (92%), injection site erythema (74%), injection site pain (67%), injection site swelling (48%)[Ref]

Nervous system

Very common (10% or more): Headache (50%)

Frequency not reported: Encephalitis, encephalomyelitis, encephalopathy[Ref]


Very common (10% or more): Fatigue (48%), malaise (37%), feeling hot (32%), rigors (21%), exercise tolerance decreased (11%)[Ref]


Frequency not reported: Myocarditis, pericarditis, ischemic heart disease, non-ischemic dilated cardiomyopathy[Ref]


Very common (10% or more): Erythema (22%), rash (11%)

Frequency not reported: Erythema multiforme major (including Stevens-Johnson syndrome)[Ref]


Very common (10% or more): Myalgia (46%)[Ref]


Very common (10% or more): Lymph node pain (57%)

Common (1% to 10%): Lymphadenopathy[Ref]


Frequency not reported: Ocular complications, blindness[Ref]


Frequency not reported: Generalized vaccinia, severe vaccinial skin infections, eczema vaccinatum[Ref]


Very common (10% or more): Nausea (19%), diarrhea (16%)

Common (1% to 10%): Constipation, vomiting[Ref]


Common (1% to 10%): Dyspnea[Ref]


1. (2020) "Product Information. ACAM2000 (smallpox vaccine)." Emergent BioSolutions Inc.

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Some side effects may not be reported. You may report them to the FDA.