Abstract：Objective To learn the characteristics of varicella breakthrough cases aged under 14 years in Haizhu District, Guangzhou City and the effects of vaccination on incidence of breakthrough cases, so as to provide the basis for improving varicella vaccination strategy. Methods Data of varicella cases aged under 14 years and vaccination in Haizhu District were collected through Chinese Disease Prevention and Control Information System and Guangdong Provincial Vaccination and Vaccine Circulation Management Information System from 2015 to 2022. Temporal distribution, population distribution and vaccination history of varicella breakthrough cases were descriptively analyzed. Effects of primary immunization age and inoculation interval on breakthrough interval were analyzed using least square method fitting bi-cubic functional equation. Results A total of 4 008 varicella breakthrough cases aged under 14 years were reported in Haizhu District from 2015 to 2022, accounting for 29.16% of all varicella cases. There were mainly 1-dose breakthrough cases, with 3 607 cases accounting for 90.00%. The proportion of 1-dose breakthrough cases showed a downward trend, while the proportion of 2-dose breakthrough cases showed an upward trend (both P<0.05). The epidemics peaked from March to May and from November to January, with a male-to-female ratio of 1.41︰1. The age of onset was mainly at 4 to 6 years, with 1 189 cases accounting for 29.67%. The primary immunization age was mainly ranged from 12 to <24 months, with 2 662 cases accounting for 66.42%. Vaccination of the second dose was concentrated at the age of 48 to <60 months, with 136 cases accounting for 33.92%. The breakthrough interval was relatively long among cases with primary immunization age at 12 to <36 months and inoculation interval within 45 months, with a median breakthrough interval of 25.24 (interquartile range, 20.00) months. Primary immunization age and inoculation interval were negatively correlated with breakthrough interval (P<0.05). Conclusions The varicella breakthrough cases aged under 14 years in Haizhu District from 2015 to 2022 were mainly occurred at the beginning of the new term, with a high incidence among preschool children. It is recommended that children receive the first dose of varicella vaccine within 36 months of age and booster within 45 months of interval.
