Friday, May 7, 2010

Deterrence/Prevention of Chickenpox (Varicella)

The American Academy of Pediatrics (AAP) recommends excluding affected children from school until the sixth day of rash.
This may not prevent spread of varicella because the child is infective before the rash appears.


Varicella vaccine consists of live attenuated Oka strain varicella virus. The vaccine is safe and highly immunogenic. It was approved for use in the United States in 1995 and has greatly reduced the incidence and mortality due to varicella.

The vaccine has been found to have protective efficacy of 71-100% against varicella. However, protection against moderate and severe varicella is much higher (95-100%).

Babies are born with protective maternal antibodies to varicella. The half-life of these antibodies is about 6 weeks, and most children have very low levels beyond age 5 months.

However, the varicella vaccine is recommended after age 1 year. A single dose provides protection to approximately 85% of recipients. Vaccine-conferred immunity to varicella wanes over time, making more vaccine recipients susceptible to the disease. The Advisory Committee on Immunization Practices (ACIP) and the AAP now recommend 2 doses of this vaccine for all children.

After the first dose at age 12-15 months, the second dose should be administered at age 4-6 years. All persons who have received one dose of the vaccine at any time in the past should be offered a second dose.
Two doses of the varicella vaccine provide 98% protection against varicella, and 100%protection against severe disease. These children also have a lower incidence of breakthrough varicella.

Breakthrough disease involves varicella that occurs after 42 days of immunization. When it occurs, it is usually mild disease but can spread to other susceptible individuals. These children usually have less than 50 skin lesions, and fever is low and quickly subsides. Headache, sore throat, malaise, and anorexia are less frequent.

Some studies have found that breakthrough disease is more common if the vaccine was given prior to age 14 months, within 28 days after the measles-mumps-rubella (MMR) vaccine, and if the child was on oral steroid therapy. Duration between vaccination and exposure has also been found to be significant.Other studies have not found such associations.

Research study protocols allow varicella vaccine administration to patients with leukemia while they are in remission. Seroconversion is good among children with leukemia.

Postexposure prophylaxis, if provided within 36-72 hours of contact, can prevent or attenuate disease in the exposed individual.This property allows the use of the vaccine to control outbreaks by vaccinating susceptible children.
Outbreaks do occur, even with high levels of vaccination.
Vaccinated children develop milder disease but are infectious. Outbreaks can be controlled by offering catch-up vaccination to unimmunized children and adolescents in the area.

Varicella Author: Parang N Mehta, MD

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