Vaccinia Virus

The dosage and administration of Vaccinia virus depend entirely on the specific product being used. Healthcare providers must follow the specific protocols for each vaccine type.

ACAM2000 (Replicating Vaccine)

• Primary Vaccination: A single dose is administered via the percutaneous route using a bifurcated needle. The needle is dipped into the reconstituted vaccine and then used to make 15 rapid 'jabs' in a 5mm area on the upper arm. The jabs should be vigorous enough to draw a trace of blood.
• Revaccination: For individuals previously vaccinated, the same 15-jab technique is used.
• Success Criteria: The 'take' (a pustule or vesicle) must be evaluated 6 to 11 days after vaccination. If no 'take' is observed, the vaccination is considered unsuccessful and must be repeated.

JYNNEOS (Non-Replicating Vaccine)

• Standard Regimen: Two doses (0.5 mL each) administered subcutaneously, usually in the upper arm.
• Dosing Interval: The second dose is administered 4 weeks (28 days) after the first dose.
• Alternative Administration: During public health emergencies, the FDA has authorized intradermal administration (0.1 mL) for certain populations to increase vaccine supply.

• ACAM2000: This vaccine is generally not recommended for routine use in children unless there is a high-risk exposure scenario (e.g., a smallpox outbreak). The safety and efficacy in the pediatric population have not been established in clinical trials.
• JYNNEOS: In August 2022, the FDA issued an Emergency Use Authorization (EUA) allowing JYNNEOS to be used in individuals younger than 18 years who are at high risk for mpox infection. However, standard approval is for adults 18 and older.

Renal Impairment

No dosage adjustments are required for patients with renal impairment, as the virus is not cleared by the kidneys in a manner that would affect its safety profile in the absence of systemic infection.

Hepatic Impairment

No dosage adjustments are required for patients with hepatic impairment. However, patients with severe liver disease should be monitored for overall immune competence.

Elderly Patients

Clinical studies of Vaccinia vaccines did not include sufficient numbers of subjects aged 65 and over to determine if they respond differently than younger subjects. In general, the immune response may be less robust in the elderly due to immunosenescence (the natural aging of the immune system).

Vaccinia virus vaccines are administered only by trained healthcare professionals in a clinical setting.

• ACAM2000 Care: The vaccination site must be covered with a non-adherent bandage (like gauze) and then a semi-permeable dressing (like Tegaderm). This prevents the live virus from spreading to other parts of the body or to other people. The site must be kept dry; if the bandage becomes wet, it must be changed immediately.
• JYNNEOS Care: No special site care is required other than standard post-injection monitoring.
• Storage: ACAM2000 must be stored at -20°C to -15°C until reconstitution. JYNNEOS is stored frozen at -25°C to -15°C.

For JYNNEOS, if the second dose is missed at the 28-day mark, it should be administered as soon as possible. There is no need to restart the series. For ACAM2000, the 'dose' is a single event, but if the 'take' is unsuccessful, it is treated as a missed successful vaccination and must be repeated.

An 'overdose' of a live vaccine refers to the administration of too much viral material or accidental inoculation at multiple sites.

• Signs: Excessive local inflammation, large necrotic lesions, or systemic symptoms like high fever and lymphadenopathy (swollen lymph nodes).
• Management: In cases of severe adverse reactions to the replicating vaccine, Vaccinia Immune Globulin Intravenous (VIGIV) or antiviral medications like tecovirimat (TPOXX) may be administered under the guidance of public health authorities.

> Important: Follow your healthcare provider's dosing instructions. Do not adjust your dose or attempt to treat the vaccination site with over-the-counter medications without medical guidance.

The side effect profile of Vaccinia virus is significant, particularly for the replicating (ACAM2000) formulation. Common reactions include:

• Injection Site Reactions: Redness, swelling, and itching at the site. For ACAM2000, this includes the formation of a pustule that eventually scabs. This is a normal part of the 'take.'
• Lymphadenopathy: Swelling of the lymph nodes, usually under the arm where the vaccine was given. This can be tender and may last for several weeks.
• Systemic Symptoms: Malaise (feeling generally unwell), fatigue, headache, and muscle aches (myalgia). These typically peak 7 to 14 days after vaccination with ACAM2000.
• Fever: A temperature of 100°F or higher is common as the immune system responds to the virus.

• Rashes: Some individuals develop 'roseola vaccinia' or other generalized rashes that are not infectious but represent an immune response.
• Severe Local Reactions: Excessive swelling of the arm or significant pain at the vaccination site.
• Chills and Rigors: Intense shivering associated with the onset of fever.

• Accidental Autoinoculation: This occurs when a person touches the live vaccine site and then touches another part of their body (e.g., eyes, nose, genitals), spreading the virus to that area.
• Generalized Vaccinia: A condition where vaccinia lesions appear on various parts of the body in otherwise healthy individuals. This is usually self-limiting.
• Erythema Multiforme: A skin reaction that can look like 'targets' or 'bullseyes,' representing a hypersensitivity reaction.

> Warning: Stop taking Vaccinia Virus and call your doctor immediately if you experience any of these symptoms.

• Myocarditis and Pericarditis: Inflammation of the heart muscle or the sac surrounding the heart. Symptoms include chest pain, shortness of breath, and a racing or pounding heart. This is a known risk with ACAM2000, occurring in approximately 1 in 175 primary vaccinees.
• Encephalitis/Encephalomyelitis: Inflammation of the brain or spinal cord. Symptoms include severe headache, confusion, seizures, or focal neurological deficits.
• Eczema Vaccinatum: A severe, potentially fatal skin reaction that occurs in people with a history of eczema or atopic dermatitis. The virus spreads rapidly across the skin, causing extensive lesions.
• Progressive Vaccinia (Vaccinia Necrosum): A rare, life-threatening condition where the vaccination site does not heal but continues to expand, destroying tissue. This occurs almost exclusively in severely immunocompromised people.
• Ocular Vaccinia: Infection of the eye, which can lead to corneal scarring and permanent vision loss.

Most side effects of Vaccinia virus are acute and resolve within a month. However, some complications can have long-term consequences:

• Scarring: The 'take' from ACAM2000 almost always leaves a permanent, small, circular scar on the upper arm.
• Cardiac Damage: In rare cases, severe myocarditis can lead to long-term heart rhythm issues or reduced cardiac function.
• Vision Loss: If ocular vaccinia occurs and is not treated aggressively, it can result in permanent blindness in the affected eye.

ACAM2000 carries a significant FDA Black Box Warning regarding cardiac and neurological risks:

• Myocarditis and Pericarditis: Clinical trials showed that about 1 in 175 people who received ACAM2000 for the first time developed heart inflammation. This can be asymptomatic or severe.
• Encephalopathy: Rare but serious brain inflammation can occur.
• Shedding: The live virus at the vaccination site can be spread to others, causing serious complications in contacts who are pregnant, immunocompromised, or have skin conditions.
• Risk of Death: Serious complications from the vaccine can be fatal in rare instances.

Report any unusual symptoms to your healthcare provider immediately. Adverse events should also be reported to the Vaccine Adverse Event Reporting System (VAERS).

Vaccinia virus vaccines, particularly the replicating strains, are among the most reactogenic vaccines used in modern medicine. They require strict adherence to safety protocols to prevent both personal injury and the spread of the virus to others. Patients must be screened for a wide range of contraindications before receiving a live-virus dose.

ACAM2000 (Live Replicating Vaccinia Virus):

1. 1Myopericarditis: There is a significant risk of myocarditis (heart muscle inflammation) and pericarditis (lining inflammation). Data suggests a rate of 5.7 per 1,000 primary vaccinees based on cardiac enzyme monitoring.
2. 2Neurological Disorders: Encephalitis, encephalomyelitis, and peripheral neuropathy have been reported.
3. 3Fetal Vaccinia: Vaccination during pregnancy can cause fetal infection, leading to stillbirth or neonatal death.
4. 4Transmission: The live virus can be transmitted from the vaccinee to household contacts or other close associates. Contacts with eczema, pregnancy, or immunodeficiency are at high risk for severe complications if they contract the virus.

• Allergic Reactions: Anaphylaxis is rare but possible. The vaccine contains trace amounts of antibiotics (neomycin and polymyxin B) and glycerin. Patients with known allergies to these components must inform their provider.
• Skin Conditions: Anyone with a history of eczema or atopic dermatitis (even if the condition is not currently active) must not receive the replicating vaccine due to the risk of Eczema Vaccinatum.
• Immunosuppression: Patients with HIV/AIDS, leukemia, lymphoma, or those taking immunosuppressive drugs (chemotherapy, high-dose steroids) are at extreme risk for Progressive Vaccinia.
• Eye Protection: It is critical not to touch the vaccination site and then the eyes. Ocular vaccinia is a medical emergency that can lead to blindness.

• Cardiac Monitoring: Patients should be advised to monitor for chest pain or shortness of breath for at least 3-4 weeks after vaccination.
• Site Evaluation: For ACAM2000, a follow-up visit is required 6-11 days after the procedure to verify the 'take.'
• Laboratory Tests: In research or exposure settings, PCR (polymerase chain reaction) tests may be used to confirm the presence of Vaccinia virus in lesions.

Vaccinia virus does not typically cause immediate impairment. However, if a patient develops a high fever, severe headache, or malaise in the weeks following vaccination, they should avoid driving or operating heavy machinery until symptoms resolve.

There is no direct interaction between alcohol and the Vaccinia virus. However, alcohol can dehydrate the body and suppress the immune system. It is generally advised to avoid heavy alcohol consumption for several days following vaccination to allow the immune system to respond optimally.

Unlike daily medications, a vaccine cannot be 'discontinued' once administered. However, for the 2-dose JYNNEOS series, if a severe allergic reaction occurs after the first dose, the second dose must not be given. For ACAM2000, if the site becomes infected with bacteria (secondary infection), antibiotic treatment is required, but the viral process will continue until the immune system clears it.

> Important: Discuss all your medical conditions and the health status of your household members with your healthcare provider before starting Vaccinia Virus.

• Immunosuppressive Therapies: Drugs such as cyclosporine, tacrolimus, azathioprine, and high-dose systemic corticosteroids (e.g., prednisone >20mg/day for >2 weeks) must not be used concurrently with replicating Vaccinia vaccines. These drugs prevent the immune system from containing the virus, leading to systemic, life-threatening viral spread.
• Chemotherapy/Radiation: These treatments severely deplete white blood cells, making the administration of a live virus extremely dangerous.

• Other Live Vaccines: Generally, other live vaccines (like MMR or Varicella) should be given either on the same day or separated by at least 4 weeks. If given too close together, the immune response to one or both vaccines may be diminished due to 'viral interference.'
• Antiviral Agents: Drugs like cidofovir or tecovirimat (TPOXX) are active against poxviruses. If these are taken during the vaccination period, they may inhibit the replication of the vaccine virus, potentially rendering the vaccine ineffective.

• Aspirin (in Children): While Vaccinia is not the flu, there is a theoretical risk of Reye's Syndrome if aspirin is used to treat fever in children receiving a live virus vaccine. Acetaminophen is the preferred fever reducer.
• TNF Inhibitors: Biologics like adalimumab or etanercept can increase the risk of infection from the live vaccine.

There are no known food interactions with Vaccinia virus vaccines. Patients may maintain their normal diet. However, maintaining hydration is important if a fever develops.

• Echinacea: Some believe this herb stimulates the immune system. While not strictly contraindicated, its effect on the specific immune response to Vaccinia has not been studied.
• High-dose Vitamin C: No known negative interaction, but it will not prevent vaccine side effects.
• St. John's Wort: No known interaction with the vaccine virus.

• Tuberculin Skin Test (PPD): Live viral vaccines can cause a temporary suppression of T-cell reactivity, leading to a false-negative result on a TB skin test. If a PPD test is needed, it should be done on the same day as vaccination or delayed for 4-6 weeks.
• Cardiac Enzymes: Following ACAM2000, tests for Troponin or CK-MB may be falsely elevated if the patient is developing subclinical myocarditis.

For each major interaction, the mechanism usually involves either the impairment of the host immune response (leading to toxicity/spread) or direct inhibition of viral replication (leading to reduced efficacy). Management strategies always involve a careful risk-benefit analysis by a physician, often involving a delay in vaccination until immunosuppressive treatments are completed.

> Important: Tell your doctor about ALL medications, supplements, and herbal products you are taking, as well as the health status of those you live with.

Conditions where the replicating Vaccinia Virus (ACAM2000) must NEVER be used include:

1. 1Severe Immunodeficiency: This includes patients with HIV/AIDS, cellular immune deficiencies, or those undergoing organ transplants. The mechanism is the inability of the body to stop viral replication, leading to Progressive Vaccinia.
2. 2Eczema or Atopic Dermatitis: Even a history of these conditions is an absolute contraindication. The skin barrier defect allows the virus to spread across the skin (Eczema Vaccinatum), which can be fatal.
3. 3Pregnancy: The virus can cross the placenta and infect the fetus (Fetal Vaccinia), leading to fetal death.
4. 4Infants <12 Months: The risk of post-vaccinial encephalitis is significantly higher in infants.
5. 5Severe Allergy: Known hypersensitivity to any component of the vaccine (e.g., polymyxin B, neomycin).

Conditions requiring a careful risk-benefit analysis (often called 'precautions'):

• Active Skin Conditions: Psoriasis, severe acne, or burns should heal before vaccination to prevent autoinoculation.
• Cardiac Risk Factors: Individuals with three or more risk factors for heart disease (hypertension, diabetes, high cholesterol, smoking) should be evaluated carefully due to the risk of myopericarditis.
• Breastfeeding: It is unknown if the virus is excreted in human milk, but the risk of physical transmission to the infant from the site is high.

Patients with known allergies to other Orthopoxvirus products or specific antibiotics used in the manufacturing process (Neomycin, Polymyxin B) may experience cross-allergic reactions.

> Important: Your healthcare provider will evaluate your complete medical history and the health of your household contacts before prescribing Vaccinia Virus.

Vaccinia virus (replicating) is contraindicated during pregnancy. According to the FDA, it is classified as a high-risk agent for fetal harm. Fetal vaccinia is a rare but devastating complication where the fetus develops skin lesions and organ failure. If a pregnant woman is inadvertently vaccinated or is a close contact of a vaccinee, she must be monitored closely by a maternal-fetal medicine specialist. The non-replicating JYNNEOS vaccine is generally considered safer, but data is still limited; its use in pregnancy is reserved for cases where the risk of orthopoxvirus infection outweighs the potential risks of the vaccine.

Live replicating Vaccinia virus has not been studied in breastfeeding women. The primary concern is not necessarily the passage of the virus into milk, but the accidental transmission of the virus from the mother's vaccination site to the infant's skin or mouth. If vaccination is necessary, extreme care must be taken to cover the site, or breastfeeding should be temporarily discontinued until the scab falls off.

ACAM2000 is not approved for children under 18 in non-emergency settings. Historical data from the 1960s and 70s showed that children, especially those under age 1, were at higher risk for neurological complications like post-vaccinial encephalitis. JYNNEOS is currently used in children under 18 only under Emergency Use Authorization during outbreaks.

In the elderly, the immune response to Vaccinia may be diminished. Furthermore, older adults are more likely to have underlying cardiac conditions that could increase the risk of complications from myocarditis. Healthcare providers should perform a thorough cardiovascular screening before administering the replicating vaccine to patients over 65.

Renal impairment does not change the initial immune response to the vaccine. However, patients with end-stage renal disease (ESRD) are often functionally immunocompromised and should be monitored for signs of systemic viral spread if a replicating vaccine is used.

There are no specific dose adjustments for hepatic impairment. Because the vaccine is not metabolized by the liver, the primary concern is the patient's overall health and ability to mount an immune response.

> Important: Special populations require individualized medical assessment and often require the use of non-replicating vaccine alternatives.

Vaccinia virus is a live-virus vaccine. Its molecular mechanism involves the infection of host cells at the site of administration. The virus enters the cell via fusion with the plasma membrane. Unlike most DNA viruses, Vaccinia replicates entirely within the host cell's cytoplasm, using its own viral enzymes for DNA replication and transcription. This process triggers the host's 'danger signals' (PAMPs - Pathogen-Associated Molecular Patterns), which are recognized by Toll-like receptors. This leads to the production of interferons and cytokines, which recruit T-cells and B-cells to the site, creating a long-lasting 'memory' of the orthopoxvirus antigens.

The pharmacodynamics of Vaccinia are measured by the 'seroconversion rate'—the percentage of people who develop a specific level of antibodies. For ACAM2000, a successful 'take' is a surrogate marker for an effective immune response. The duration of effect is significant; while booster doses are recommended every 3-10 years for high-risk individuals, some level of immune memory can persist for decades.

| Parameter | Value |

|---|---|

| Bioavailability | N/A (Local replication) |

| Protein Binding | N/A |

| Duration of Shedding | 14-21 days (ACAM2000) |

| Tmax (Antibody Peak) | 4-6 weeks post-vaccination |

| Metabolism | Cellular proteolysis |

| Excretion | Scab exfoliation (Viral particles) |

Vaccinia is a complex virus, not a simple chemical compound. It has a linear, double-stranded DNA genome of approximately 190,000 base pairs, encoding about 200 proteins. The virus particle is brick-shaped and large enough to be seen under a high-powered light microscope. It is stable in a freeze-dried state but highly sensitive to UV light and common disinfectants (like bleach or 70% ethanol).

Vaccinia Virus belongs to the Live Vaccinia Virus Vaccine [EPC] class. It is the only member of this class used for smallpox/mpox. It is distinct from 'Inactivated' vaccines (like the Salk Polio vaccine) or 'mRNA' vaccines (like COVID-19 vaccines) because it contains a whole, functional virus.