Rationale
Chickenpox is a highly contagious disease, with an attack rate of at least 90 percent among susceptible individuals and those who were not protected by any form of vaccination. Both sexes are infected equally—that is, there is no predisposition with regards to sex. Children between the ages of 5 and 9 are most commonly affected and account for 50 percent of all cases. The incubation period of chickenpox ranges between 10 and 21 days, but more often than not it ranges between 14 and 17 days.

Clinically, chickenpox presents as rash, low-grade fever, and malaise. The skin lesions, the hallmark of the infection, consist of maculopapules, vesicles, and scabs in varying stages of evolution. If you are infected with chickenpox, you cannot report to work because you are highly contagious. Thus, you will lose a lot in terms of monetary income because of foregone productivity.

The worst sequelae of varicella are the appearance of shingles later in life. It is an established fact that when you recover from varicella, the virus will hibernate in some of your nerves. When your resistance weakens in the future, this virus will wake up and reappear causing shingles which is manifested as severe pain along the course of your nerves in your chest. With this long-term complication, in addition to having foregone productivity while suffering from varicella many years back, there is urgent need to have this vaccination.

Generic and brand names
The generic name is a lyophilized preparation of the live attenuated Oka strain of a varicella-zoster virus. The brand names are Varilrix or Varivax.

Composition of the vaccine
The vaccine contains lyophilized preparation of the live attenuated Oka strain of varicella-zoster virus, obtained by propagation of the virus in MRC5 human diploid cell culture.

Mechanism of action
When the vaccine is administered to you and to other recipients, antibodies against the disease are produced, and the overall seroconversion rate was higher than 98% six weeks after the first dose vaccination. This means that almost 100% of all those who availed of the vaccination has acquired the protection from being afflicted with varicella after receiving the first dose.

Schedule of administration
For adults, from age 13 and onwards, the first dose of 0.5 ml reconstituted vaccine is administered at an elected date. The second dose will be given after 6 to 10 weeks from the first dose.

Indications and usage
This vaccine is indicated for active immunization against varicella of healthy subjects from age 12 months onwards. It is also indicated for high-risk patients and susceptible healthy close contacts, such as the following:

• Patients with acute leukemia
  If you have been suffering from leukemia, you are recognized to be at increased risk when you develop varicella and should receive this vaccine if you have no history of the disease or are found to be seronegative. If are immunized in the acute phase of your leukemia, your maintenance chemotherapy should be withheld one week before and one week after your immunization. If you are undergoing radiotherapy, the vaccine will not be administered during your treatment phase.
• Patients under immunosuppressive therapy or treatment
  If you are under immunosuppressive therapy (including corticosteroid therapy) for malignant solid tumor or for serious chronic diseases, such as chronic renal failure, auto-immune diseases, collagen diseases, and severe bronchial asthma, the vaccine will not be administered to you because you are predisposed to severe varicella.
  If you are in complete hematological remission from the disease, then you can be immunized with the vaccine. However, you need to undergo blood examination wherein the total lymphocyte count should be at least 1,200 per mm3 or no other evidence of lack of cellular immuno-competence.
• Patients with planned organ transplantation
  If organ transplantation (e.g. kidney transplant) is being planned and considered for you, then immunization should be carried out a few weeks before the administration of the immunosuppressive treatment.
• Patients with chronic diseases
  If you have been suffering from other chronic diseases, such as metabolic and endocrine disorders, chronic pulmonary and cardiovascular diseases, mucoviscidosis and neuromuscular abnormalities, then you are prone to contract severe varicella. Thus, you need to be vaccinated with this vaccine.
• Healthy close contacts
  Your susceptible healthy close contacts should be immunized in order to reduce the risk of transmission of the virus to high-risk patients. These include parents and siblings of high-risk patients, and medical, paramedical personnel and other people who are in close contact with varicella patients or high-risk patients.

Precautions

• After reconstitution, this vaccine should be used immediately. Alcohol and other disinfecting agents must be allowed to evaporate from the skin before injecting the vaccine since they may inactivate the virus;
• Appropriate medical treatment should always be readily available in case of rare anaphylactic reactions following the administration of the vaccine. For this reason, the vaccine should remain under medical supervision for 30 minutes after immunization;
• This vaccine should never be injected intradermally nor intravenously;
• If you have received immune globulins or a blood transfusion, immunization should be delayed for at least 3 months.

Side effects

• Healthy subjects
  Reactions at the site of injection are usually mild and transient. A rash is reported in less than 4% of patients. Most of them occur during the first three weeks after immunization and the number of lesions is generally below ten. Temperature above 37.50 C (axillary)/ 380 C (rectal) is reported in approximately 5% of subjects during a six-week follow-up of the vaccines. The incidence of vaccine-related general symptoms, such as a headache, fever, paresthesia, and fatigue was equal or less than 2.5% after each dose.
• High-risk patients
  Reactions at the site of injection are usually mild. Rash accompanied by mild to moderate fever have appeared a few days up to several weeks after immunization. Such reactions have occurred in less than a quarter of leukemic patients. These eruptions were generally mild and short-lived. They tend to occur in the more immunosuppressed leukemic patients such as those still in the maintenance phase of chemotherapy. The appearance of these eruptions did not influence the clinical management of the patients. There is no evidence that immunization may have an adverse effect on the course of the disease.

Dosage and mode of administration
For adults, the dose consists of 0.5 ml of reconstituted vaccine, and it is administered subcutaneously. No other routes of administration are allowed.