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Essential Recipients The varicella vaccine prevents a disease that affects nearly every human at some time. Certain children are at high risk for varicella: Children with chronic heart or lung disease. Children with immunodeficiency disorders. HIV infection/AIDS, if the CD4 counts are above 15% of normal. Leukemia, when the child is in remission and off chemotherapy for 3-6 months. Children who require long term steroid or salicylate therapy (the vaccine is given when they are off these drugs for a while). Children attending day care centres. Adolescents who have never had chicken pox, especially if they are leaving home for a residential educational institution.
Breakthrough Varicella Chicken pox developing in a child who has received the vaccine more than 42 days previously is known as breakthrough varicella. It implies a failure of protection. Chicken pox signs prior to 42 days may be because of the vaccine virus itself, or because of infection acquired before the protection provided by the vaccine became effective. Breakthrough varicella is usually a mild disease. There are usually 50 or fewer skin lesions, fever and other symptoms are mild, and the disease has infrequent complications. However, people with breakthrough varicella are as infectious to others as are people with regular varicella. Children who have received the varicella vaccine many years ago are more likely to have breakthrough varicella. Children who were vaccinated at the age of 15 months or greater are less likely to have breakthrough varicella than are those who received the vaccine at 12 months.

The Varicella Vaccine

Though varicella is usually a gentle disease, it causes serious and life threatening situations in some children. This is especially likely in children with conditions that reduce the body's defenses, and in teenagers and older people. Even in normal children, it leads to significant illness, school absenteeism, and difficulties for the parents. The varicella vaccine can avoid this sickness, safely and fairly effectively. It has been found to be 70% effective in preventing chicken pox, and 95% effective in preventing serious chicken pox disease.

The varicella vaccine was developed in Japan in the 1970s, and consists of a live virus. The virus has been weakened, so that it causes an infection in the vaccinated person, but no significant disease. The infection causes the body's immune system to react by producing antibodies against varicella. If the child gets infected with chicken pox at some later time in life, the antibodies will prevent the infection developing into chicken pox disease. Protective factors develop in 95-99% of people who receive this vaccine.

This vaccine has been in use in Japan since 1989, and in the USA since 1995. It's safety is now well established, though the efficacy has recently been questioned.

Dosage

The varicella vaccine is supplied as a single dose container. When mixed, the dose is about 0.5 ml, and this is given to a child subcutaneously, that is, under the skin. The vaccine is heat sensitive, and must be stored carefully in a refrigerator, and administered within 30 minutes of preparation.

Earlier, a single dose was recommended in children below 13, and 2 doses in people over the age of 13 years. However, a single dose is associated with reducing immunity over time, and breakthrough varicella occurs often. Currently, the recommendation is for two doses of this vaccine for all children.

The first dose can be given at any age after 12 months. However, giving the vaccine after the age of 14 or 15 months seems to reduce the occurrence of breakthrough varicella.

Side Effects

This vaccine has fairly mild side effects. Some children may have soreness at the injection site, but this is not severe as the injection is given shallowly, under the skin, rather then deep into the muscle. Fever and a chicken pox like rash occur in a few children — these are generally mild and short lived.

Since this is a live virus vaccine, it should not be given to pregnant women, and young women receiving it must be warned to avoid pregnancy for 4 weeks.

It can cause severe infection in people with reduced immunity. Children with leukemia, AIDS/HIV infection, those receiving treatment that reduces immunity, and those with other conditions that reduce the body's defences, should receive this vaccine with great care.

Also see: Chicken Pox (Varicella)

Last revision: September 24, 2007

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