January 15 , 2008
CHICKEN POX: ILLNESS AND VACCINATION
Amy Movius MD
A school in Lincoln recently had 6 students come down with chickenpox. As a result of this outbreak, students who had not been previously infected or immunized against this infection were banned from attending school for 16 days. Chickenpox has been around forever, so what was the big deal??
To understand this approach, it is important to first understand what chickenpox infection actually is. Chickenpox is a very common (usually) childhood illness. Prior to vaccine availability, there were 4 million cases each year in the US. It is caused by the varicella-zoster virus and is VERY contagious. It is spread mostly through the air (cough, sneezing, breathing) and 80-90% people casually exposed will be infected. The symptoms don’t start until 2-3 weeks after being exposed (incubation period). The main symptom is a very itchy rash and fever, which can be quite uncomfortable. However, the person is infectious a day or two before the rash shows up. Likewise, the infection can continue to be passed on until all areas of the rash are scabbed over, usually 5-6 days (infectious period).
The long incubation and infectious periods are why the susceptible students in Lincoln were kept out of school for so long, rendering chickenpox very inconvenient as well as uncomfortable. The perception still exists, though, that chickenpox is a minor illness. Unfortunately, this is not always true. 1 out of 500 children and 1 out of 50 adults with chickenpox require hospitalization. Complications of chickenpox include serious skin infections (including MRSA and group A or “flesh-eating” streptococci), brain infections, and pneumonia. These can be fatal. Adults are 10-20 times more likely to have a complication with chickenpox. Chickenpox during pregnancy can pose a serious risk to the fetus, as well. Even in uncomplicated chickenpox, the virus never leaves the body and can be reactivated later in life in the form of “shingles”.
Vaccine against chickenpox was first made available in the US in 1995 given in a single dose after 12 months of age. In 1999 the CDC expanded the recommendation to any child in childcare or entering elementary school. In 2005 the recommendation was expanded that it be required for entry into school from kindergarten to college. As of 2005, approximately 88% of children receive the chickenpox vaccine. The vaccine is between 70-90% effective at preventing disease and those who do have “breakthrough” disease tend to have milder cases.
The positive results of vaccination are impressive. There has been about an 80% decrease in the cases of chicken pox compared to before vaccine was available. There has been an 88% decrease in hospitalization and a 92% decrease in deaths from chickenpox. The side effects are minimal, and primarily include arm soreness and occasionally a few (<25) spots. In April 2007 the American Academy of Pediatrics increased the vaccination to 2 doses. This was prompted by a steady occurance of outbreaks over the last 5-6 yrs of chickenpox that includes immunized and some un-immunized persons, especially in 9-11yr olds. With 2 doses of vaccine, >99% people have immunity by blood test. Immunity persists for 10 yrs in 98% and virtually 100% of severe infections are eliminated. Breakthrough cases are 3.3 times less likely than in people receiving 1 vaccine dose.
Increasing the doses of chickenpox vaccine is one of those rare circumstances where more is truly better. There is no age cut off for receiving vaccine, so adults should speak to their providers for vaccine consideration as well.
References:
American Academy of Pediatrics Committee on Infectious Diseases. Policy Statement: Prevention of Varicella: Recommendations for Use of Varicella Vaccines in Children, Including a Recommendation for a Routine Two-Dose Varicella Immunization Schedule
U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National Center for Immunization and Respiratory Diseases.