[Analysis of protective effect of using chickenpox live attenuated vaccine among 4-17 years old children in Minhang district, Shanghai].

OBJECTIVES

To survey on the vaccination of varicella live attenuated vaccine among 4-17 children in Minhang District, and analyze the protective effect against varicella.

METHODS

We collected outbreak chickenpox cases reported from infectious disease report system and surveillance units in Minhang district from 1st May in 2012 to 30th Apr in 2013. The 1: 3 matched case-control study was conducted to questionnaire the legal guardian of the cases and control group, and calculate the protective effect and effective term of protection. The survey included vaccination, chickenpox exposure history, previous history of varicella illness, suffering from the symptoms of chickenpox, the vaccinations brand, etc. The criteria of accepted case were those healthy students who were in the same class with those chickenpox cases. The accepted matched controlling data were those children who were from the same class with outbreak chickenpox cases without varicelliform eruption, similar live condition, the closest house, the same gender, the closest age. This study investigated 390 cases of patients and the control group included 1 170 cases. Chi-square test was used to compare the vaccination of cases and controls, as well as the incidence of chickenpox vaccination different brands VarV, Mantel-Haenzel chi-square test was applied to compare the protective effect of the two groups.

RESULTS

VarV overall vaccination rate was 68.3% (1 065/1 560), among them, the case group coverage was 45.1% (176/390), significantly lower than the control group (76.0% (889/1 170)) (χ² = 128.55, P < 0.01). The coverage in children of 4-10 years old group was 88.4% (375/424), significantly higher than the 11-17 years old group (60.7% (690/1 136)) (χ² = 109.40, P < 0.01). The overall protective effect of VarV was 78.10% (71.82%-82.98%).Vaccinated group incidence ratio was 16.5% (176/1 065), significantly lower than the unvaccinated group (43.2% (214/495)) (χ² = 128.55, P < 0.01). The chickenpox risk of the children who were vaccinated was lower than those who were not, and the OR (95%CI) was 0.22(0.17-0.28) . Proportion of the fever and the typical symptoms of varicella zoster were 26.1% (46/176), 8.0% (14/176) in the children vaccinated VarV, significantly lower than children without VarV vaccination history (54.7% (117/214) , 18.2% (39/214) ) (χ² values were 32.33 and 8.67, respectively. P values both <0.01). The varicella incidence was 17.4% (139/797) in children vaccinated domestic VarV, and it was 13.8% (37/268) in the group of imported VarV (χ² = 1.92, P = 0.184) . The average duration of effective protection period for domestic and imported VarV was (6.2 ± 2.7), (6.3 ± 3.4) years (F = 2.24, P = 0.136).

CONCLUSIONS

The risk of varicella incidence and the proportion of fever or typical varicella zoster were lower in the one dose of VarV vaccinated; Effective protective effect was consistent in the children with domestic or imported VarV vaccination.