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.

A retrospective test-negative case-control analysis was conducted in Brazil from July 2021 to March 2022 to estimate the vaccine effectiveness (VE) against hospitalization and severe illness in adolescents due to infection with SARS-CoV-2 variants (gamma, delta, and omicron). 

A total of 8,458 eligible individuals (12-19 years of age) hospitalized with acute respiratory syndrome, including 3,075 cases with laboratory-proven COVID-19 and 4,753 controls with negative tests for COVID-19, were enrolled. 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 aOR was used to estimate VE.

The results showed that in the pre-omicron period, VE against COVID-19 hospitalization was 88% (95% CI, 83%-92%), which dropped to 59% (95% CI, 49%-66%) during the omicron period. For hospitalized cases of COVID-19, the 2-dose schedule was moderately effective against intensive care unit admission (46%, [95% CI, 27-60]), need for mechanical ventilation (49%, [95% CI, 32-70]), severe COVID-19 (42%, [95% CI, 17-60]), and death (46%, [95% CI, 8-67]), considering the entire period of analysis. 

However, there was a substantial reduction of about 40% in the VE against all endpoints, except for death, during the omicron-predominant period. Among the cases, 240 (6.6%) adolescents died, of which 224 (93.3%) were not fully vaccinated.

In conclusion, the study showed a substantial reduction in VE against all endpoints during the omicron-predominant period among adolescents, suggesting that the 2-dose regimen may be insufficient for SARS-CoV-2 variants. The findings supported the need for updated vaccines to provide better protection against severe COVID-19.