Exploring waning COVID19 vaccine effectiveness against reinfections in the pediatric population: a retrospective population analysis
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University of Pisa, Italy
Dipartimento di prevenzione ASL Lecce, Italy
University of Salento
Publication date: 2023-04-26
Popul. Med. 2023;5(Supplement):A2005
Background and Objective:
The real-world effectiveness and duration of anti-COVID19 vaccine’s protection from reinfections in the pediatric population (5-11 years) has yet to be determined. Groups with different primary immunization were compared, in terms of duration of immunity and effectiveness for COVID19 reinfections.

In this retrospective population analysis, we analyzed data from the vaccination registry and Infections Regional Information System of Apulia region (Southern Italy) for birth cohorts 2011-2017 from 31/12/2020 to 02/12/2022. We identified three groups based on the primary immunization schedule: subjects 5-11 years old vaccinated with two doses (vaccine immunity), not vaccinated with a history of SARS-CoV2 infection (natural immunity) and individuals with a combination of both (hybrid immunity). Subjects with a SARS-CoV2 infection occurring within the first 14 days from the primary immunization course were excluded. COVID19 reinfection was defined as a positive swab after 90 days from previous infection. Data were analized using R and compared using chi-square test.

A total of 30,997 children were included (15,064 females, 15,933 males; mean age 8.31.9); 22,073 (71.2%) children were infected from SARS-CoV2 at least once and 1,533 (4.9%) had a COVID19 reinfection. Cases of reinfections and mean distance since COVID19 infection were in the vaccine immunity group 192 (1.12%) 87.855.8 days; in the natural immunity group 1,254 (9,5%) 21495.9 days; and hybrid immunity group 87 (12.3%) 155.485.5 days. We observed a significant relationship between natural immunity group and COVID19 reinfections (X =1142; p