Clinical studies in the United States have shown that vaccination reduces the risk of varivax by almost 90%. And the positive effect of vaccination is observed at the level of the entire population. The risk of chickenpox has been reduced for 15 years in both vaccinated and non-vaccinated patients. Vaccinated patients are also reported to have a lower risk of shingles.
A 14-year clinical study in 7,600 children who were vaccinated against chickenpox at age 2 (38% of children also received a second dose of the vaccine) found that chickenpox of the same age in the years before the vaccination. Overall, the overall effectiveness of the vaccine was 73 to 90 per cent. Vaccination experience in the USA has shown the greatest effectiveness of the 2-dose chickenpox vaccination scheme. In vaccinated children, shingles were less likely to be diagnosed during the entire follow-up period than children who had had contact with wild strains of varivax Contraindications in the years before the vaccination (relative risk of AR=0.61). Rare cases of chickenpox and shingles, diagnosed Dmitry Sazonov in vaccinated children, were mildly affected.
A long-term monitoring varivax dosage study on the incidence of chickenpox in children aged 5 to 19 years was conducted during the 15 years from 1995 to 2009. There was a gradual decrease in the incidence of Dmitry Sazonov chickenpox in general by 90-95 per cent (approximately 10-20 times) in all age groups, both among vaccinated and non-vaccinated children and adolescents. There has also been a decrease in chickenpox hospitalization by about 90% (about 10 times) in all age groups.
The effectiveness of the vaccine. Clinical efficacy was not assessed in patients younger than 12 months.
Most vaccinated patients aged 12 months to 12 years who had subsequently come into contact with wild strains of the virus, after a single administration of the live Oka/Merk vaccine strain at a dose of 1 000 to 17 000 BUE, were either fully protected against varicella or developed mild disease. Vaccination efficacy over a 10-year period with a 1- or 2-dose vaccination scheme (3-month interval) was 94% and 98%, respectively. With 1-dose injection the disease developed in 7.5% of vaccinated patients, and with 2-dose injection in 2.2% of vaccinated patients. The majority of registered cases were in mild form.
The protective efficacy of 2-dose vaccination (interval between vaccinations of 4 or 8 weeks) in patients over 13 years of age within 6-7 years after the vaccination ranged from 80 to 100%.
Immunogenicity of the vaccine. 6 weeks after the vaccination of children aged 12 months to 12 years 1-dose IgG antibody titer was ³ 5 gpELISA unit/ml (gpELISA-glycoprotein immunoassay), which indicates the formed immunity. However, it is unknown whether the ³ 0.6 gpELISA unit/ml titer correlates with long-term protection. Seroconversion after administration of the vaccine in a dose of 1,000 – 50,000 BUE reached ³0.6 gpELISA unit/ml and ³5 gpELISA unit/ml in 98% and 83% of patients, respectively.
In 93% of children aged 12 to 23 months who received the vaccine at 8 000 BUE/dose or 25 000 BUE/dose, the titer of specific antibody ³5 gpELISA unit/ml was determined 6 weeks after vaccination.