Chicken Pox (Varicella) Vaccine

Dr. Parang Mehta, MD.

Chicken pox was a universal disease till a few years ago. Everyone would get it at some time or other in a lifetime. The USA used to have 4 million cases of chicken pox a year, and about a hundred deaths, before the varicella vaccine was introduced. In areas where the majority of children are vaccinated, varicella is uncommon now.

The varicella vaccine was developed in Japan for use in children at high risk of severe varicella. In the early years it was given only to children with leukemia, and other children at high risk for getting severe chicken pox. It was licensed for general use in children in ther USA in 1995.

The vaccine has been found to be safe and quite effective. It is most effective in the first few years after vaccination. Vaccine efficacy tends to wane with time, after three years. However, even those children who do get chicken pox in spite of vaccination (Breakthrough Varicella, see sidebar) will have mild disease.

The vaccine is also useful in preventing the disease in susceptible people who have come in contact with someone who has chicken pox. It must be given within three days of the contact for this purpose (post-exposure prophylaxis).

Vaccine Doses

The vaccine should be given to all children above 12 months (preferably 14 months) of age. A single dose only is recommended at present for all children upto the age of 13 years. If a child has not received the chicken pox vaccine in early childhood, it should be given at 11-12 years. With breakthrough varicella being seen frequently now, a second dose of the vaccine for all children is being debated.

People above the age of 13 need 2 doses of the varicella vaccine. The second dose should be 4-8 weeks after the first.

The dose is always the same for all people — 0.5 ml, given subcutaneously (that is, just under the skin, not deep into the muscle like most other vaccines).

Adverse Reactions

On the whole, the chicken pox vaccine is well tolerated. Only about 20% of people receiving it have minor side effects like pain, redness or swelling at the site of the injection. Some children (less than 5%) will develop a rash similar to chicken pox.

Very few children have serious adverse reactions to the varicella vaccine. Most of these are allergic reactions to some vaccine component.

Contraindications

The varicella vaccine is a live virus vaccine. It sets up a mild infection in healthy children, which does not harm the child, but stimulates the immune system to produce defensive factors against chicken pox. However, children with diseases of the immune system are unable to deal effectively with even this weakened virus, and the vaccine virus can cause severe disease in them.

The following people should not receive varicella vaccine:

Is It A Good Vaccine?

Well, it is open to debate at present. It protects against chicken pox, which is not always a mild disease. Before the vaccine was introduced, the USA used to have four million cases of chicken pox every year, several thousand hospitalisations, and about a hundred deaths annually.

Since the vaccine has been recommended for all children, the occurrence of chicken pox has reduced by 80%. However, the vaccine itselt is not itself a hundred percent reliable. Its protective efficacy is about 85-95% against chicken pox, which means that some vaccinated children will get the disease. However, these children usually have mild chicken pox. The protective efficacy of the varicella vaccine against severe chicken pox is nearly 100%.

There is some concern that the protection of the varicella vaccine lasts only a few years. This means that vaccination is only postponing the age of acquisition of chicken pox in the population. Since chicken pox is a serious disease at older ages, this is a major worry.

 

Chicken Pox in Children
Prevention of Chicken Pox
Chicken Pox/ Varicella for health care professionals, also by Dr. Parang Mehta

 

Last revision: September 16, 2011

Breakthrough Varicella

Chicken pox that occurs in children who have been vaccinated is called breakthrough varicella, if it occurs more than 6 weeks after completing the vaccination. The varicella vaccine has been found to be 70-90% effective at preventing chicken pox.

Breakthrough varicella is more likely when:

Breakthrough varicella is usually much milder than typical chicken pox. The rash usually consists only of red flat or raised lesions. Fluid or pus filled blisters (vesicles and pustules) are uncommon in breakthrough varicella. There is usually no fever, or only mild fever, and most affected children have fewer than 50 skin rash lesions.

Children with breakthrough chicken pox are also infectious. They should not attend school or daycare till the time when no new lesions are forming in the skin rash. If vesicles were present, they must all be crusted.

Uses of Varicella Vaccine

Most commonly, it is used in normal healthy children, as a protective measure. This is aimed at protecting children against chicken pox.

It is also used as a protective agent in children exposed to chicken pox. Chicken pox is highly infectious, and contact with a case is a high risk situation. Given within 3 days of such contact, the varicella vaccine can usually prevent the development of chicken pox in exposed children. If chicken pox does occur, it is usually mild.

Contact Information

Dr. Parang Mehta,
Mehta Childcare,
Opposite Putli, Sagrampura,
Surat. Tel: +91 98241 53923.
Email: