New Chickenpox Vaccine Formulation Approved In Canada

MONTREAL, QC -- May 14, 2003 -- Varivax® III (varicella virus vaccine, live, attenuated (OKA/Merck)) a third-generation version of Varivax -- the first vaccine indicated for immunization against chickenpox in healthy individuals 12 months of age and older, has been approved by Heath Canada.

Varivax III prevents chickenpox with the same safety and efficacy profile as previous formulations of Varivax. The new Varivax III offers the added convenience of being refrigerator-stable for up to 18 months.

"Most people consider chickenpox a harmless disease. However, each year 350,000 Canadians will develop chickenpox and 1,900 of them will experience complications that require hospitalisation", said Dr. Ross A. Pennie, Paediatrician and Paediatric Infectious Diseases Specialist at the McMaster Medical Centre. "Vaccination against chickenpox is highly recommended since, in rare cases, it can lead to some very serious, even life-threatening complications such as severe group A streptococcal infections."

The Canadian National Advisory Committee on Immunization (NACI), the Canadian Paediatric Society and the College of Family Physicians of Canada, as well as the American Committee on Immunization Practices, the American Academy of Pediatrics, and the American Academy of Family Practitioners, all recommend varicella vaccination.

Varivax Shown to Provide a Stronger Immune Response
Using a well-defined test(1) known as the gpELISA (not commercially available), a recent clinical study(2) compared Varivax with the only other chickenpox vaccine available in Canada. The study showed that both Varivax and Varilrix™ are well-tolerated but six weeks after vaccination, 95.2 per cent and 97.1 per cent of individuals receiving Varivax reached a gpELISA (greater or equal than) 5 units compared to 85.6 per cent for the Oka-RIT varicella vaccine (Varilrix™). To date, Varivax relies on the most important body of clinical evidence with trials involving more than 17,000 healthy individuals and post-marketing evaluation of more than 89,000 patients.

The Disease
Varicella or chickenpox is caused by the varicella-zoster virus (VZV), a member of the herpes virus family, the same virus that causes herpes zoster or shingles. VZV is highly contagious, easily spread by direct contact with skin lesions or oral secretions or through airborne transmission. People with varicella are infectious from one to two days before the rash appears and until all lesions have dried up.

Symptoms usually occur anywhere from 10 to 21 days after contact with the VZV. There may be fever, malaise and upper respiratory tract infection before or as the characteristic rash develops. Generally, the skin rash appears in successive waves during the first three to four days of illness, scabbing over fairly quickly. If no complications occur, the healing process lasts for about two to three weeks.

The Complications
Chickenpox has the potential to cause serious complications. A prospective study published in Pediatrics(3), shows varicella-zoster virus infection in children is associated with a 58-fold increased risk of acquiring invasive group A streptococcal (GAS) disease. GAS can in turn lead to streptococcal toxic shock syndrome and necrotizing fasciitis, popularly known as flesh-eating disease.

The study found an overall case fatality rate of four per cent and concluded that universal chickenpox vaccination could potentially prevent up to 15 per cent of all paediatric cases of invasive GAS disease. Other specific complications can include bacteremia (bacterial infection in the blood), osteomyelitis (bone infection), septic arthritis (infection in the fluid and tissues of a joint), endocarditis (infection of the inner lining of the heart and its valves), otitis media (middle ear infection) and scarring.

Varivax III
Varivax III is the third-generation version of Varivax, originally launched in Canada in December 1998. Like its predecessors, Varivax III is a live, attenuated virus vaccine, a lyophilized preparation of the Oka/Merck strain of varicella.

Varivax III can be stored at refrigerated temperatures of between 2 degrees C to 8 degrees C for up to 18 months, whereas Varivax II could only be stored in a refrigerator for up to 90 days.

The safety and efficacy of Varivax III is identical to Varivax II.
A recently published study of the Oka/Merck strain of varicella in clinical practice found the effectiveness of the vaccine to be 85 per cent and 97 per cent against moderately severe and severe disease respectively.(4) More than 30 million doses of Varivax have been administered in various countries including the United States, Brazil, Hong Kong, Malaysia, Taiwan and Canada.

Dosage
For those 12 months to 12 years, the dose is 0.5 ml subcutaneously, individuals 13 years or older require two 0.5 ml doses administered four to eight weeks apart. Varivax III comes in a single-dose vial as a powder that is reconstituted with a diluent just prior to being administered by subcutaneous injection. Varivax III can be given at the same time as other routine childhood vaccines such as the measles, mumps and rubella virus vaccine (M-M-R II).

References:

(1) Li S et al., Inverse relationship between 6-week postvaccination varicella antibody response and likelihood of long-term breakthrough infection. Pediatr Infect Dis J 2002;21:337-342.

(2) Lau YL, Vessey SJR, Chan ISF, et al. A comparison of safety, tolerability and immunogenecity of Oka/Merck varicella vaccine and VARILRIX(TM) in healthy children. Vaccine, 20, 2002; 2942-2949.

(3) Laupland KB, Davies HD, Low DE, et al. Invasive Group A Streptococcal Disease in Children and Association with Varicella-Zoster Virus Infection. Pediatrics. May 2000; 105

(4) Vasques M, LaRussa PS, Gershon AA, Steinberg SP, et al. The effectiveness of the varicella vaccine in clinical practice, New England Journal of Medicine, 2001; 344; 955-60.


SOURCE: Merck Frosst Canada Ltd.

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