The following is a summary of “Vaccine Effectiveness against SARS-CoV-2 Variants in Adolescents from 15 to 90 Days after Second Dose: A Population-Based Test-Negative Case-Control Study,” published in the FEBRUARY 2023 issue of Pediatrics by Oliveira et al.

For a study, researchers sought to investigate the vaccine effectiveness (VE) against hospitalization and severe illness caused by SARS-CoV-2 variants (gamma, delta, and omicron) in adolescents.

A test-negative, case-control analysis was conducted from July 2021 to March 2022. The study included 8458 eligible individuals aged 12-19 years hospitalized with acute respiratory syndrome. Of these, 3,075 cases had laboratory-proven COVID-19, and 4,753 controls had negative tests for COVID-19. The primary exposure of interest was vaccination status, and the primary outcome was SARS-CoV-2 infection during gamma/delta vs. omicron-predominant periods. The VE was estimated using the aOR to associate prior vaccination and outcomes.

In the pre-omicron period, the VE against COVID-19 hospitalization was 88% (95% CI, 83%-92%) but decreased to 59% (95% CI, 49%-66%) during the omicron period. For hospitalized cases of COVID-19 during the entire analysis period, the 2-dose schedule showed moderate effectiveness against intensive care unit admission (46%, [95% CI, 27-60]), mechanical ventilation requirement (49%, [95% CI, 32-70]), severe COVID-19 (42%, [95% CI, 17-60]), and death (46%, [95% CI, 8-67]). There was a significant reduction of approximately 40% in the VE against all endpoints, except for death, during the omicron-predominant period. Among cases, 240 (6.6%) adolescents died; of these fatal cases, 224 (93.3%) were not fully vaccinated.

The VE against all endpoints was substantially reduced during the omicron-predominant period among adolescents. The findings suggested that the 2-dose regimen may be insufficient for SARS-CoV-2 variants and emphasized the need for updated vaccines to provide better protection against severe COVID-19.

Reference: https://www.jpeds.com/article/S0022-3476(22)00861-7/fulltext