[COVID-19 vaccine safety: results of active surveillance at a sentinel site in ArgentinaSegurança das vacinas contra COVID-19: resultados da vigilância ativa em uma unidade sentinela da Argentina].

Objective: To analyze the results of surveillance of adverse events of special interest (AESI) within the context of the COVID-19 vaccination campaign at a sentinel site in Argentina. The retrospective (pre-vaccination) period was compared with the prospective (vaccination) period to identify safety signals.

Methods: Retrospective and prospective search for AESI based on ICD-10 hospital discharge codes. A descriptive analysis, moving-averages trend smoothing, and control charts were used to detect changes in AESI behavior.

Results: A total of 1,586 AESI were identified. Analysis of the proportion of AESI codes at hospital discharge revealed an increase during the pandemic period (2020) and a progressive decrease during the vaccination period (2021-2022), accounted for by the incidence of acute respiratory distress syndrome (ARDS). Moving-average smoothing and control charts were compared to identify time points at which the proportion of AESI exceeded the upper limits of control. During the vaccination period, this occurred for ARDS, thrombosis, myocarditis, meningoencephalitis, multisystem inflammatory syndrome, and anaphylaxis. No differences were observed for Guillain-Barré syndrome, thrombocytopenia, or pericarditis. Acute disseminated encephalomyelitis, meningoencephalitis, and pericarditis events during the vaccination period all occurred in subjects with no history of vaccination.

Conclusion: Active sentinel-site surveillance allowed identification of AESI occurring at a higher frequency during the vaccination period compared to the pre-vaccination baseline. The protective effect of the vaccine against COVID -19 was clearly observed, as manifested especially by a reduction of ARDS cases in the post-vaccination period. This strategy is useful for assessing vaccine safety by identification of safety signals.