Epidemiological study and serological evaluation on post-exposure vaccination on an outbreak of varicella in elementary school in Shanghai

OBJECTIVE To investigate an outbreak of varicella in elementary school and carry out serological evaluation on post-exposure vaccination so as to provide reference for varicella prevention and control in school. METHODS Medical record of varicella cases, vaccination status and history on varicella of children who were from the same classrooms were collected. Finger tip bloods from children with post-exposure vaccination were collected before vaccination , 2 weeks after vaccination and 4 weeks after vaccination. The level of varicella IgG antibody was tested by enzyme-linked immunosorbent assay (ELISA). RESULTS There were 13 cases of varicella and the attack rate reached 9.29% in children from the same class. The attack rate in non-vaccinated children (33.33% ) was higher than those vaccinated (7.58% ). Vaccine efficacy ( VE) was 77.26%. The positive rate of varicella IgG before post-exposure vaccination, 2 weeks after vaccination and 4 weeks after vaccination were 72.73%, 100%, 100% respectively. The geometric mean concentration after vaccination was higher than those before vaccination. Moreover the geometric mean concentration of 2 weeks after vaccination was higher than those 4 weeks af - ter vaccination. CONCLUSION Vaccination is effective in varicella prevention. It is suggested that children should have another 1 dose of varicella vaccination four years after the first dose. Post-exposure vaccination is effective in improving varicella IgG antibody level in short time and controlling of the disease.