Chicken Pox



Varicella (“Chicken Pox”) used to be an extremely common childhood illness characterized by fever, malaise, and a very itchy rash consisting of, on average, between 250-500 small blisters that appear then dry up over the course of about 5 days. In children with normal, intact immune systems, Varicella was almost always a benign, self limited disease. Complications did occur, but were very rare prior to puberty. Occasionally (about 1 case out of 100) either a bacterial infection of the skin or pneumonia – both of which are easily treated with antibiotics – might occur. More rarely (once approximately every 43,000 cases in normal children) a life threatening complication involving inflammation of the brain, liver, or lungs happened. The latter was much more common among children with weak immune systems; including those with HIV, other immune deficiencies, those who are on cancer chemotherapy, radiation treatment, kidney dialysis, or taking certain drugs such as those we give after an organ transplant or, more commonly, high dose steroids. Varicella can also occasionally cause birth defects if a pregnant woman catches it in the first or second trimester – this is again rare, only 2% of babies born to such mothers will be affected this way, 98% will come out just fine despite mother’s infection. Varicella is not dangerous at all in the third trimester or to newborns.

Varicella is one of the most contagious diseases known. The chance of a person who has not already had it coming down with the illness after being exposed is 80-90%. Because of this, most unvaccinated people used to get it in childhood – more than 90% of people over age 18 years in the United States have had it already. Some of these people don’t even know they’ve had it! This is because some very mild cases may not show much of a rash, and thus some people can get Chicken Pox without it being recognized for what it is. This occurs most often in young infants, because in general the younger a child when they get Varicella the milder the case and the less sick with it they become. As a result, if you do blood tests on adults who believe they “have never had Chicken Pox”, you discover that, in fact, 70% of even that group has. Conversely, an adult who truly has never had Chicken Pox has reason to worry… an adult who gets Chicken Pox will often be far sicker than the typical child and is at significantly higher risk for complications (although not so high as an immunocompromised individual would be). Generally, people can only get Chicken Pox once, after which they will be “immune” for life. Rarely, second and even third cases do occur in an individual – usually this is when the first case was very mild, treated with an antiviral drug, or when an immune system problem is present.

Varicella is caused by the Varicella-Zoster Virus (VZV), which is closely related to both Herpes and Epstein-Barr Virus, the cause of Mononucleosis. What all the viruses in this “herpes family” have in common is that they continue to live inside the body for the rest of one’s life after primary infection. They are not killed or eliminated from your body like most other viruses, but instead become “latent”. Latent VZV can reactivate and cause “Shingles” – a painful crop of small blisters in a small patch anywhere on the body (usually the trunk), and someone with Shingles can give someone who’s never had it Chicken Pox. Shingles only occurs in about 15% of people with latent VZV, however, and most often not until they reach old age at that. While painful, Shingles itself is also harmless and self limited except in immunocompromised individuals.

The vaccine against Varicella ,Varivax, is a live-virus type vaccine – a strain of VZV that has been weakened or “attenuated” in the laboratory so that it doesn’t cause such severe disease. About 10% of recipients will get a mild rash, with only about 5-10 lesions occurring either at the injection site or elsewhere. About 25% have some pain, redness, and swelling at the injection site. A low grade fever may occur. An allergic reaction is possible due to small amounts of the antibiotic Neomycin in the vaccine, and known allergy to this drug is a contraindication to giving the vaccine. No other side effects to Varivax have been reported. The only other contraindications to giving it are immune deficiency or significant acute illness. It can be given simultaneously with other vaccines.
Varivax is very effective in preventing SEVERE Chicken Pox, but it does not prevent Chicken Pox altogether. Even after receiving the vaccine, about 30% of children exposed to Varicella will still come down with the disease. They will get a much milder case, however. As “wild-type ” or non-vaccine varicella is very rare these days, the recommendation is for all children to undergo routine vaccination between 12-18 months of age and to have a booster dose before Kidnergarten entry. All adolescents who have a history of having chicken pox should be tested to make sure they are immune. If they are not immune, or have only ever had a single dose of varicella vaccine, they should complete the vaccine series.

For more information, please visit Center for Disease Control & Prevention website at: