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Chicken Pox Immunization - Chicken Pox Vaccines

Chicken Pox Basics

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Updated April 28, 2014

Written or reviewed by a board-certified physician. See About.com's Medical Review Board.

Many parents -- especially those born after the era of routine polio and measles infections -- don't remember if or when they had any of the common childhood infections, such as roseola, fifth disease, or croup, etc.

But many remember when they had chicken pox (varicella). People may think of it as a mild disease, but if after 20 or 30 years, you can still remember feeling sick for a week with an itchy rash all over your body, it was likely pretty bad. This was in the days before a vaccine existed, so most kids went through the rigors of chicken pox

Fortunately, we now have a vaccine, which spares most of today's kids from the itchy rash -- or missing out on not only a week of school, but also having to forgo trick-or-treating on Halloween, which happened to me when I got chicken pox when I was about eight years old.

Chicken Pox Immunization

A chicken pox vaccine was first licensed by the FDA in 1995, after being used in Japan and Korea since 1988.

It was added to the U.S. routine child immunization schedule in 1996, with a recommendation for routine use for all children at twelve to eighteen months of age. A catch-up vaccination plan was also put in place at 11 to 12 years for older kids who are unvaccinated and hadn't caught chicken pox yet.

Recommendation for a chicken pox booster dose began in 2006.

Chicken pox immunization rates are generally very good. It is estimated that about 90% of toddlers are vaccinated against chicken pox, which has helped chicken pox cases drop by about 93% in many areas. Many states even require that kids get at least one dose of the chicken pox vaccine before starting school.

Chicken pox immunization is very effective against severe chicken pox infections - the type that would require hospitalization or that could be fatal. One dose of the chicken pox vaccine is 95 to 97% effective against severe disease.

Unfortunately, it is only about 70 to 90% effective against any infections, which means that some children can still develop mild cases of chicken pox even after getting the vaccine.

Severe infections are the real target of chicken pox immunization plans, though, as before routine use of the chicken pox vaccine, about 11,000 people were hospitalized with chicken pox each year, and 100 to 150 died.

Chicken Pox Vaccines

There are two different chicken pox vaccines, both live virus vaccines, for kids:

  • Varivax - a monovalent (one disease) vaccine that can protect kids against chicken pox
  • ProQuad - a quadrivalent (four diseases) vaccine that can protect kids against measles, mumps, rubella, and chicken pox

The current recommendations are that infants receive their first dose of the chicken pox vaccine when they are 12 to 15 months old and then get a booster dose when they are four to six years old. The second dose can be given earlier though, as long as it is at least three months after the first dose.

Chicken Pox with Vaccine

Unlike unvaccinated children who get chicken pox (and who may have 200 to 500 chicken pox lesions for five to six days and a fever up to 102°F for two to three days), kids who get chicken pox after being vaccinated (known as "breakthrough varicella") with one or two doses of the chicken pox vaccine typically have much milder chicken pox symptoms.

The booster dose of the chicken pox vaccine can reduce the chance of a breakthrough infection even more than a single dose, but it still isn't 100% effective against preventing mild infections.

Some things to keep in mind about children with breakthrough varicella:

  • children will often have less than 50 chicken pox lesions - with some having only 5 to 10 lesions
  • 90% of kids won't have any fever
  • recovery is usually faster - three to five days vs. seven days for unvaccinated kids
  • mild cases of chicken pox are often confused with bug bites, especially chiggers

Also, although kids with breakthrough varicella are contagious, they are much less contagious than a regular case of chicken pox in an unvaccinated child.

Before kids got a booster dose, when breakthrough varicella did occur in schools, it is reported that 11 to 17% of exposed children who were vaccinated also got mild chicken pox vs over 70% of unvaccinated children who got a routine chicken pox infection. The use of the booster dose of Varivax will hopefully cut these rates and school outbreaks of chicken pox down even further.

What You Need to Know

To get the most out of your child's chicken pox vaccine and protection against chicken pox, also remember that:

  • Combination shots are generally preferred over single shots, except for ProQuad, since children who get ProQuad for their first dose of MMR and Varivax have been shown to have more fevers and fever related seizures than children who get the separate shots.

  • MMR and Varivax can be given at the same time, but if they aren't, since they are both live virus vaccines, they should be given at least 28 days apart.

  • Unvaccinated teens should get two doses of Varivax at least 4 weeks apart if they have never had chicken pox.

  • Varivax may prevent an unvaccinated child from getting chicken pox if given within three (and maybe five) days of exposure to someone with chicken pox. A post-exposure dose might also be a good idea if a child is exposed to chicken pox and hasn't had his booster dose yet.

  • People get chicken pox 10 to 21 days after coming into contact with someone who is still contagious, either because they have direct contact with their chicken pox lesions or because of contact with airborne droplets or infected respiratory tract secretions.

  • Children with many immune system problems, except some children with HIV, and children who are allergic to the vaccine or its components, should not be vaccinated with the Varivax vaccine.

  • The risk of developing shingles seems to be lower in kids who received the chicken pox vaccine vs. kids who had natural chicken pox infections.

Most importantly, since breakthrough chicken pox infections are often missed and misdiagnosed as bug bites, keep your suspicions high if your child has "bites" in unusual places or when he wasn't outside or exposed to anything that could have bitten him. Remember that a child's chest, abdomen, and back are more unusual places to get bites vs. his arms, legs, and waist line.



Sources:

American Academy of Pediatrics (AAP), Committee on Infectious Diseases. (2003). Varicella-zoster infections. In LK Pickering (Ed.), Red Book: Report of the Committee on Infectious Diseases (26th ed., p. 672-686).

American Academy of Pediatrics (AAP), Committee on Infectious Diseases. Prevention of Varicella: Recommendations for Use of Varicella Vaccines in Children, Including a Recommendation for a Routine 2-Dose Varicella Immunization Schedule Pediatrics July 2007; 120:1 221-231

Centers for Disease Control and Prevention. Varicella outbreak among vaccinated children: Nebraska, 2004. MMWR Morb Mortal Wkly Rep.2006;55 :749-752

Davis MM, Patel MS, Gebremariam A. Decline in varicella-related hospitalizations and expenditures for children and adults after introduction of varicella vaccine in the United States. Pediatrics.2004;114 :786-792

Epidemiology and Prevention of Vaccine Preventable Diseases. 12th Edition (April 2011)

Manual for the Surveillance of Vaccine-Preventable Diseases (4th Edition, 2008)

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