Chickenpox vaccination

Chickenpox is caused by a virus from the herpes virus group. The infection is extremely contagious. The reduction of the network of nurseries and kindergartens has led to an increase in the non-immune layer (in England and the USA - 4-20% of people aged 20-25 years), so that chickenpox (varicella) in children, adolescents and adults has become common and is more severe in them. Vaccination against chickenpox has significantly reduced the incidence of chickenpox.

After the primary infection, the varicella-zoster virus remains in the nerve ganglia and is reactivated as herpes zoster when the immune system is weakened (immunosuppression, old age). In generalized form, the infection occurs in immunodeficiencies and immunosuppression. The frequency of complications is illustrated by data from Great Britain and Ireland, where 112 cases were detected per year (frequency 0.82 per 100,000 children): 40 children had septic or toxic shock, 30 had pneumonia, 26 had ataxia, 25 had encephalitis, 7 had necrotizing fasciitis, 8 had DIC syndrome, 9 had fulminant chickenpox. 5 children died, 40% were discharged with residual manifestations (usually with ataxia and skin scars). Chickenpox causes more than half of cases of necrotizing streptococcal fasciitis in children.

In Russia, 0.5-0.8 million children and adolescents suffer from chickenpox every year (incidence rate 300-800 per 100,000), the damage in the form of quarantines and days of incapacity for parents is significant. The infection takes many lives of children on immunosuppression. Calculation of economic losses due to chickenpox showed that they are the second largest of all infectious diseases.

[ 1 ], [ 2 ], [ 3 ]

Objectives of varicella vaccination

Mass vaccination against chickenpox is included in the vaccination calendar of several countries (Japan, USA, Canada, Germany, etc.), where its cost-effectiveness has been proven. WHO recommends, first of all, introducing selective vaccination of risk groups - patients with leukemia in remission and those who have not had the disease or those awaiting transplantation. This recommendation can be implemented in Russia, since the Varilrix vaccine has been registered.

The issue of the advisability of introducing vaccination against chickenpox was considered by a group of experts from Eastern European countries. The experts noted that chickenpox is an acute problem, including in the economic aspect. The appearance in the arsenal of health care systems of a live attenuated vaccine based on the Oka strain opens up new opportunities for the prevention of chickenpox.

The accumulated experience of using preventive vaccines against chickenpox in the world allows us to apply 3 prevention strategies:

• Selective vaccination of patients at risk of complicated chickenpox, representatives of professional groups, family environment of immunocompromised patients and pregnant women. This strategy will protect the most vulnerable groups of patients without affecting the overall incidence and formation of collective immunity, it will not reduce the economic burden of the infection.
• Vaccination of contacts in the outbreak will allow outbreaks to be controlled, primarily in preschool institutions and schools. This strategy will also not affect the development of the epidemic process and the economic burden of the infection.
• Universal 2-dose vaccination of all children from 12 months of age in the strategic perspective will be able to provide economic benefits not only to the individual patient, but also to the population as a whole.

Immunity and effectiveness of the chickenpox vaccine

Administration of one dose of Varilrix provides 95% seroconversion, in persons over 12 years old - only in 78-82% of cases, two doses - in 99%, which justifies the administration of 2 doses. In children vaccinated once, upon contact, there are still cases of "breakthrough" disease, which usually proceeds mildly. When it was administered simultaneously with Priorix, a high level of seroconversion was observed (95.7%) with the same frequency of fever and exanthema. OkaVax provides 98% seroconversion after 1 dose, in 90% the duration of immunity is 20 years or more, epidemiological efficiency in the 1st year is 100%, over the next 7 years, 0.2-1.9% of people fall ill per year upon contact, which is 5-15 times lower than in unvaccinated people. Varivax prevents the disease in 83-86%, moderate and severe - in 100%. The question of a double vaccination is raised, as is the case with other live virus vaccines; in countries that have included vaccination in the calendar, it is carried out twice. Mass vaccination in the USA reduced the incidence from 1995 to 2000 by 80%, most of all in the group of children 0-4 years old. The simultaneous decrease in the incidence in older ages indicates the creation of herd immunity. The frequency of hospitalizations decreased, and the mortality (per 1 million population) fell by 66% - from 0.41 in 1990-1994 to 0.14 in 1999-2001, and in children 1-4 years old it decreased by 92%.

There are concerns that the decrease in the incidence of chickenpox may lead to an increase in the incidence of shingles due to a decrease in the natural immune boosting of those who have had chickenpox. However, these concerns have not been confirmed. The possibility of vaccination against shingles in the elderly has been proven. In the United States, since 2007, the Zostavax vaccine (Merck & Co.) has been included in the vaccination schedule for people over 60 years of age; vaccine trials have shown a decrease in the incidence of shingles by 51% (from 11.1 to 5.4 per 1000) and postherpetic neuralgia by 67% (from 1.4 to 0.5 per 1000).

Vaccination of children with leukemia has protected them during immunosuppressive therapy. Vaccination is performed during remission lasting 1 year against the background of maintenance therapy (with the number of lymphocytes> 700 and platelets> 100,000). The seroconversion rate is higher than 92%, the epidemiological effectiveness is 86%, 14% of patients usually endure chickenpox without complications. In patients with leukemia who have had chickenpox, the vaccine reduces the incidence of herpes zoster.

Chickenpox Vaccination: Vaccine Characteristics

Chickenpox vaccines registered in Russia

Vaccine	Compound
Varilrix - Live Vaccine - Glaxo SmithKline, England	Prepared from the Oka virus strain modified by 38 passages in cell cultures; contains traces of neomycin, without gelatin. A dose of 0.5 ml is administered subcutaneously or intramuscularly, starting from the age of 1 year, usually administered with other live virus vaccines. Store at 2-8° for 2 years.
Varivax® - a live vaccine from the Oka/Merck strain (Merck, Sharp and Dome, the Netherlands - is being prepared for registration)
Okavax is a live vaccine from the Oka strain (Biken Institute, Japan, exclusive distributor in Europe - Sanofi Pasteur - is preparing for registration). It does not contain gelatin.

Reactions and contraindications to the chickenpox vaccination

The reactogenicity of vaccines is low, within 1 month after the administration of Varilrix, maculopapular rashes are observed in 2-3%, and vesicular rashes in 1%. When using the OkaVax vaccine in healthy patients, an increase in body temperature was observed in 2.8%, rash in 1.7%, and local reactions in 3.2% of cases. In individuals with various pathologies, reactions were noted in 3.5%, 3.5%, and 0.9% of cases, respectively.

In patients with leukemia, rash elements, often isolated, occur in 24%. The vaccine virus can be detected in vesicles in only 1%. Temperature >38.5° is observed in 4-5% of vaccinated patients, and pain and redness at the injection site occur in 20-30% of children. Shingles is rarely detected after vaccination.

Contraindications are the same as for other live vaccines, as well as immunosuppression with a decrease in the number of leukocytes below 700 per µl. It is not recommended to take aspirin for 4 weeks after vaccination (risk of Reye's syndrome). The vaccine virus does not cause generalized pustulosis in patients with atopic eczema.

Post-exposure prophylaxis of chickenpox

When the Varilrix vaccine is administered in the first 96 hours after contact, a 90% protective effect is achieved. In cases of severe immunosuppression, contacts are given human immunoglobulin for intravenous administration and acyclovir is prescribed.