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# Attenuated Vaccines
## Overview
Attenuated vaccines contain live, weakened microorganisms that replicate in the host but do not cause disease. They elicit a strong, long-lasting immune response, mimicking natural infection.
## Primary Indications
* **Measles, Mumps, Rubella (MMR) vaccine:** Prevention of measles, mumps, and rubella.
* **Varicella (VAR) vaccine:** Prevention of chickenpox.
* **Rotavirus (RV) vaccine:** Prevention of rotavirus gastroenteritis.
* **Yellow Fever (YF) vaccine:** Prevention of yellow fever.
* **Oral Typhoid (Vivotif) vaccine:** Prevention of typhoid fever.
* **Intranasal Influenza (LAIV) vaccine:** Prevention of influenza.
## Adult Dosing
* **MMR:** 0.5 mL IM or SC x 2 doses (typically 1-2 months apart).
* **VAR:** 0.5 mL SC x 2 doses (typically 4-8 weeks apart).
* **RV (e.g., Rotarix, RotaTeq):** Oral, 1.5 mL or 2 mL depending on product, given in 2 or 3 doses, respectively, starting at 6 weeks of age.
* **YF:** 0.5 mL SC x 1 dose.
* **Oral Typhoid:** 1 capsule PO every other day for 4 doses.
* **LAIV:** 0.2 mL intranasally (0.1 mL per nostril).
## Pediatric Dosing
Dosing is based on age and specific vaccine schedule recommendations from the CDC.
* **MMR:**
* 1st dose: 12-15 months
* 2nd dose: 4-6 years
* **VAR:**
* 1st dose: 12-15 months
* 2nd dose: 4-6 years
* **RV:**
* Starting at 6 weeks of age. Specific schedule depends on product.
* **LAIV:**
* 6 months through 59 months (4 years, 11 months).
## Dose Adjustments
No dose adjustments are typically necessary based on renal or hepatic impairment.
## Contraindications
* Severe allergic reaction (anaphylaxis) to a previous dose of the vaccine or a component of the vaccine (e.g., neomycin, gelatin).
* Pregnancy (for MMR, VAR, YF). Women should avoid pregnancy for 1 month after MMR or VAR vaccination.
* Immunocompromised state (e.g., congenital immunodeficiency, HIV with severe immunosuppression, receipt of high-dose corticosteroids, chemotherapy, radiation therapy). Specific guidance for HIV-infected individuals exists.
* Active untreated tuberculosis.
* Recent receipt of blood products or immunoglobulins (may interfere with vaccine response; timing depends on product).
## Adverse Effects
Common: Fever, rash, mild injection site reactions.
Less Common: Seizures (associated with fever), arthralgia/arthritis (especially in adult women with MMR), transient thrombocytopenia.
Rare: Encephalitis (very rare, causality debated), anaphylaxis.
## Key Drug Interactions
* **Immunosuppressants:** Can reduce the efficacy of attenuated vaccines.
* **Antiviral medications:** May interfere with live attenuated influenza vaccine (LAIV). Avoid concurrent use; consider timing of administration and discontinuation of antivirals.
## Monitoring
* Monitor for signs of allergic reaction post-vaccination.
* Monitor for expected adverse effects.
* Assess immune status before administering to potentially immunocompromised individuals.
## Clinical Pearls
* Attenuated vaccines are generally more immunogenic and provide longer-lasting immunity than inactivated vaccines.
* Avoid aspirin or aspirin-containing products for at least 6 weeks after varicella vaccination due to theoretical risk of Reye's syndrome.
* Yellow fever vaccine can be administered as early as 9 months of age for travel to endemic areas, but routine recommendation starts at 12 months.
* LAIV is generally preferred over inactivated influenza vaccine for children aged 2-8 years who have not received a prior influenza vaccine, provided there are no contraindications.
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*Disclaimer: This information is intended for healthcare professionals. Always consult the most current prescribing information and local guidelines before administering any medication.*
