Varicella (Chickenpox) was, until recently, one of the most common of childhood diseases. Before there was a vaccine, almost everyone got it.

Chickenpox is caused by the varicella zoster virus (VZV).

VZV is a DNA virus and is a member of the herpesvirus group. VZV persists in sensory nerve ganglia. Primary infection with VZV results in chickenpox. Herpes zoster (shingles) is the result of recurrent infection. The virus is believed to have a short survival time in the environment.

Its most recognizable feature is an itchy rash all over the body. It also causes fever and drowsiness. It is spread from person to person through the air, by coughing, sneezing or breathing, and can also be spread by contact with fluid from the blisters.

It usually takes 2–3 weeks from the time of exposure for a person to become ill, and an infected person is contagious from 1 or 2 days before the rash appears until all the blisters are dried up, usually 4 to 5 days after.

Chickenpox is usually mild, but it occasionally causes serious problems. The blisters can become infected, and some children get encephalitis. Among infants less than 1 year old who get the disease, about 1 in 250,000 die. For older children, about 1 in 100,000 die. If a woman gets chickenpox just before or after giving birth, her baby can get very sick, and about 1 in 3 of these babies will die if not treated quickly. About 1 child in 500 who gets chickenpox is hospitalized (about 1 in 50 adults). After a person has chickenpox the virus stays in the body. Years later it can cause a painful disease called herpes zoster, or shingles.

DESCRIPTION

The active ingredient in Chickenpox vaccine is a live but weakened varicella-zoster virus, which is the cause of chickenpox. This specially weakened virus is called the Oka strain.

Chickenpox vaccine is a vaccine containing the varicella-zoster virus that causes chickenpox. The virus in the vaccine has been weakened so that it does not cause chickenpox in normal healthy people. When a person is given the vaccine, the immune system (the body’s natural defence against infections) makes antibodies against the chickenpox virus and also reacts to the virus in other ways to develop what is called cell-mediated immunity. These antibodies and cell responses help to protect you against getting chickenpox.

Many people get chickenpox during childhood, but some get it only as teenagers or adults when it may be a much more severe infection, even in healthy people.

Chickenpox vaccine may sometimes be given to healthy children between 1 and 12 years of age who live with, or spend a lot of time with, people who have poor immune systems and who are likely to be very seriously ill if they catch chickenpox. Vaccinating these healthy children to prevent them getting chickenpox means that they will not then pass the infection on to people in whom chickenpox can be a very serious disease.

Like other vaccines, Chickenpox vaccine cannot completely protect you against catching chickenpox. However, people who have had the vaccine and still catch chickenpox usually have a very mild disease with very few spots and blisters compared with people who have not had the vaccine.

If a teenager or adult comes into contact with a case of chickenpox or shingles before both doses of Chickenpox vaccine have been given or within about 6 weeks after the second dose, the vaccine may not be able to prevent chickenpox. Similarly, a child who comes into contact with a case of chickenpox just before or within about 6 weeks after vaccination may still get chickenpox.

Chickenpox vaccine is supplied as a slightly cream to yellowish or pinkish coloured pellet in a single dose glass vial with a separate glass ampoule of clear colourless sterile liquid (Water for Injections) for making up the vaccine. After mixing with the water the vaccine is clear peach to pink in colour.

Each 0.5 milliliter (ml) dose contains not less than 103.3 plaque forming units (Oka strain) of chickenpox virus.

DOSAGE AND ADMINISTRATION

Children between 15 months and 12 years of age

Only one dose of 0.5 ml is given subcutaneously.

Adults and adolescents from 13 years of age

Two doses, each of 0.5 ml, are given subcutaneously to complete the course with an interval of approximately 8 weeks (minimum 6 weeks) between the first and second doses. There is no information on the use of Chickenpox vaccine in the elderly.

Although Chickenpox vaccine is not intended for routine use in children, it may be given to children between 15months and 12 years of age to prevent them getting chickenpox and passing the infection on to people in whom chickenpox can be a very serious disease. After one dose of single-antigen varicella vaccine, 97% of children 15 months to 12 years of age develop detectable antibody titers. More than 90% of vaccine responders maintain antibody for at least 6 years. Among healthy adolescents and adults 13 years of age and older, an average of 78% develop antibody after one dose, and 99% develop antibody after a second dose given 4 to 8 weeks later.

Immunity appears to be long-lasting, and is probably permanent in the majority of vaccinees. Breakthrough infection is significantly milder, with fewer lesions (generally fewer than 50), many of which are maculopapular rather than vesicular. Most persons with breakthrough infection do not have fever.

Chickenpox vaccine must be injected under the skin usually in the upper arm. Your nurse or doctor may wipe the skin with alcohol or other disinfecting agents and will let the skin dry before the injection.

Your doctor or nurse will take care that Chickenpox vaccine is not injected into skin or the bloodstream.

If the appointment for the second injection is missed, the second dose should still be given as soon as this can be arranged after the due date. The second injection will ensure that protection against chickenpox will be continued.

If exposure to varicella does not cause infection, postexposure vaccination should induce protection against subsequent exposure. If the exposure results in infection, there is no evidence that administration of varicella vaccine during the incubation period or prodromal stage of illness increases the risk for vaccine-associated adverse reactions. Although postexposure use of varicella vaccine has potential applications in hospital settings, preexposure vaccination of all healthcare workers without evidence of varicella immunity is the recommended and preferred method for preventing varicella in healthcare settings.

Varicella outbreaks in some settings (e.g., child care facilities and schools) can persist up to 6 months. Varicella vaccine has been used successfully to control these outbreaks.

SCHEDULE

Varicella, Hepatitis A and Pneumococcal Conjugate vaccines should be offered only after one to one discussion with parents. Also refer to the individual vaccines notes for recommendations.

ADVERSE EVENTS

Like all vaccines, Chickenpox vaccine can have side effects.

In teenagers and adults, the second dose was not more likely than the first dose to cause side effects.

Very rarely, a severe allergic reaction may occur with symptoms that may include facial swelling, low blood pressure, difficulty breathing, going blue and loss of consciousness. Urgent medical attention is needed in these cases. These reactions often occur very soon after the injection, while still in the clinic. If any of these symptoms or other serious symptoms are noticed after vaccination, you must seek urgent medical help.

The commonest side effects (reported in greater than 1 in 10 persons) seen in clinical trials with Chickenpox vaccine were reactions at the site of the injection. These included local redness, local pain and swelling.

Side effects that were commonly reported during clinical trials (in more than 1 in 100 but less than 1 in 10 persons) were tiredness, raised temperature, headache, and spots or blisters that usually occurred near the site of the injection but sometimes at other sites.

Side effects that were uncommonly reported during clinical trials (in more than 1 in 1000 but in less than 1 in 100 persons) were: inflammation or a small lump under the skin at the site of injection, chest pain, feeling generally unwell, pain at other sites, dizziness, migraine, stomach upset, feeling sick, joint pain, back pain, muscle pain, drowsiness, coughing, sore throat, runny nose, itching, and swelling of the glands.

Other side effects that have been reported very rarely (in less than 1 in 10,000 persons) during routine use of the vaccine are rashes with spots and blisters, loss of movement or sensation in one or more parts of the body, inability to walk properly, and low numbers of a type of blood cell called thrombocytes that are needed for normal blood clotting.

CONTRAINDICATIONS AND PRECAUTIONS

Chickenpox vaccine is not suitable for everyone.

Chickenpox vaccine must not be given if the answer is “Yes” to any of the following:

Has the person who is to receive Chickenpox vaccine:

• had an allergic reaction to Chickenpox vaccine following the first dose?
• had an allergic reaction to any other chickenpox vaccine, or to neomycin, or to any of the ingredients listed above?
• any illness that weakens the immune system (such as blood disorders, or infections)?
• recently received or still taking any treatment that can weaken the immune system?

Also, is the person who is to receive Chickenpox vaccine:

• pregnant or even possibly pregnant?
• breastfeeding?
• under 13 years of age? Chickenpox vaccine will not usually be given to children who are less than 13 years old. It may be given to children between the ages of 1 and 12 years of age to prevent them getting chickenpox and passing the infection on to people in whom chickenpox infections can be a very serious disease.

Chickenpox vaccine will, or may be, delayed if the answer to the following is “Yes”:

• Does the person who is to receive Chickenpox vaccine have a high temperature or an infection?
• Has the person who is to receive Chickenpox vaccine had a blood or plasma transfusion, or human immunoglobulin within the last 3 months? If so, the antibody response to Chickenpox vaccine may be low so it is usual to wait for 3 months before giving Chickenpox vaccine.
• Is the person who is to receive Chickenpox vaccine due to undergo treatment that might weaken their immune system?

Take special care with Chickenpox vaccine

If the answer is “Yes” to any of the following questions, talk to your doctor or nurse before the vaccine is given.

Does the person who is to receive Chickenpox vaccine:

• come into regular contact with pregnant women?
• come into regular contact with people for whom the chickenpox virus could cause serious health risks, such as people who have a weak immune system or people receiving any treatment that can weaken the immune system?

STORAGE

To maintain potency, all varicella-containing vaccines must be stored frozen at an average temperature of 5°F (-15°C).

You should store Chickenpox vaccine in a refrigerator between 2°C and 8°C until it is given. The vaccine in powder form is not affected by freezing. The doctor or nurse should check that the expiry date on the outer package label has not passed.

The vaccine diluent should be stored separately at room temperature or in the refrigerator. The vaccine should be reconstituted according to the directions in the package insert and only with the diluent supplied.

Keep this vaccine out of the sight and reach of children.

Once the vaccine has been mixed with the water supplied, it should not be frozen and should be injected as soon as possible. It may, however, be kept for up to 90 minutes at room temperature (25°C) and up to 8 hours in the refrigerator (2°C-8°C). If not used within these time limits, the vaccine must be discarded.

PRESENTATION

103.3 PFU/0.5 ml, powder and

solvent for solution for injection.

Chickenpox vaccine also contains inactive ingredients. These are amino acids, human albumin, lactose, neomycin sulphate, sorbitol and mannitol.