Varicella (Chicken Pox) Vaccine

Dr. Parang Mehta, MD.

Chicken pox is a viral disease, and before the vaccine became available, almost everyone got it at some time or other. It is highly infectious, and almost everyone coming in close contact with a person who has chicken pox will end up getting the disease. Unfortunately, chicken pox is infectious for 1-2 days before the rash becomes visible. Thus school exclusion and isolation policies are not adequate to avoid spread of this disease.

The Varicella Vaccine

The varicella vaccine has been in use in Japan for over forty years now. It was licensed in the USA in 1995, and has reduced chicken pox occurrence and deaths causes by chicken pox by about 80%. It is a safe and effective vaccine.

It consists of live, weakened chicken pox virus, which is injected into the body. This will stimulate the body to produce antibodies to the varicella virus, thus making the vaccine recipient immune to chicken pox. This vaccine has a protective efficacy of over 95% in the first year, but efficacy wanes after that. However, though chicken pox may occur in children who have received the vaccine, it is usually very mild. Severe chicken pox and fatal disease almost never occur in vaccinated persons.

When a child gets chicken pox, he or she also develops lifelong immunity to the disease. Second attacks of chicken pox are very rare. However, the vaccine does not provide as good protection. Vaccine induced protection wanes with time, and some children will get breakthrough varicella when exposed to the disease.

Varicella Vaccine Schedule

Varicella vaccine is recommended for all children at the age of 12-15 months. A second dose is recommended at the age of 4-6 years. Children who have not received the vaccine at the appropriate age, can be vaccinated at any age later. Children who have had chicken pox usually have lifelong immunity to this disease, and should not be vaccinated.

The second dose can be given earlier than the age of 4-6 years. However, at least three months should have elapsed since the first dose was given. If, for some reason, a second dose was given at a lesser interval (but 28 days or more), it need not be repeated.

The earlier recommendation was only a single dose for children under the age of 13 years. Children who have received one dose of the varicella vaccine should receive another, at any age, if they have not suffered varicella in the interval.

Varicella vaccine is given subcutaneously (under the skin). It is available alone, as well as in combination with the MMR (measles, mumps, and rubella) vaccine.

Breakthrough Varicella

This is chicken pox occurring in vaccinated children. It is more common in children who have received only a single dose of the varicella vaccine, and in those who were exposed to chicken pox several years after the last dose of vaccine. Other reasons for breakthrough varicella could be poor quality vaccine, improper storage or administration, or immune deficiency of the child.

Breakthrough varicella is usually a mild disease. Most children have fifty or fewer skin lesions, and the fever is low. The disease lasts a shorter time than normal chicken pox. However, these children are as infectious to others as are unvaccinated children with chicken pox. A child with breakthrough varicella can also start an outbreak in school or daycare.

Post-Exposure Prophylaxis

The use of the varicella vaccine to prevent the disease after exposure to a person with chicken pox is called post exposure prophylaxis. For best effect, it must be given within 3 days of the exposure to a person with chicken pox. The vaccine, will, of course give long term immunity against chicken pox.

For children too young to take the vaccine, the recommended prophylaxis is varicella zoster immune globulin (VZIG). This injection provides immediate protection against chicken pox, but the protection lasts only a few weeks. Another option is the drug acyclovir.

Contraindications

Varicella vaccine is generally safe, but should not be given under certain circumstances.

Side Effects

The most common side effect of the varicella vaccine are local redness, pain and swelling, which happens in about a quarter of recipients. 4-5% of recipients may have a chicken pox like rash, though much milder. The rash generally has only a few skin lesions. A few children may have fever.

Herpes zoster has been reported after the varicella vaccine. This can occur even many years after the vaccination. However, the incidence is much less after varicella vaccine than after chicken pox disease.

Last Revision: July 2, 2020