Long-term Response to SARS-CoV-2 mRNA Vaccine in Adolescents

The COVID-19 pandemic's transition to an endemic phase emphasizes the importance of vaccination. Despite initial strong immunogenicity, waning of vaccine-induced immunity requires further investigation. Therefore, this study evaluated the immunogenicity of the BNT162b2 vaccine in adolescents, focusing on spike-specific and neutralizing antibody kinetics following primary and booster vaccinations as well as the impact of breakthrough infections.

This observational study included 157 adolescents 12-17 years old who received the primary BNT162b2 vaccine and 22 participants who received booster doses. Antibody levels were measured at 1, 3, 5 and 10 months post-vaccination and post-booster. Breakthrough infections were identified using SARS-CoV-2 antigen/polymerase chain reaction tests. Safety was monitored by tracking adverse effects.

Post-primary vaccination, the geometric mean titer of anti-spike antibodies decreased significantly over time, with a 2.3-fold reduction after 10 months. Booster doses induced higher antibody titers, which also waned over time, albeit more slowly. Breakthrough infections significantly boosted neutralizing titers, including those against variants such as Delta and Omicron. Long-term adverse effects were minimal, with only 7 cases of transient lymph node enlargement and menstrual irregularities.

The BNT162b2 vaccine induced robust initial immune responses in adolescents; however, the immunity waned over time. Booster doses are essential for sustained protection, especially against emerging variants. Breakthrough infections further enhance antibody responses, highlighting the benefits of hybrid immunity. The safety profile is generally favorable; however, ongoing monitoring is warranted.