Antibody titer trends after SARS-CoV-2 vaccination in patients aged 12-25 years with underlying diseases.

Background: Whereas declines in antibody titers after SARS-CoV-2 vaccination have been reported, most reports are predominantly from adults. Long-term trends in SARS-CoV-2 antibody titers after the first BNT162b2 vaccination series in children and young adults with underlying diseases remain less studied.

Methods: This prospective single-center observational cohort study enrolled patients aged 12-25 years with underlying diseases who received the first BNT162b2 vaccination series. At least three longitudinal antibody titers were evaluated during the first year following vaccination.

Results: Among 429 study subjects, 61 patients with at least three subsequent antibody titer measurements were included. The median (interquartile range [IQR]) time intervals from the vaccination to the first, second, and third antibody measurements were 43 (30-56), 126 (110-155), and 224 (207-256) days, and antibody titers declined with median (IQR) values of 2310 (1440-3515), 2010 (1165-3055), and 1410 (904-2195) U/mL, respectively. In 35 immunocompetent patients, the antibody titers decreased consistently in each measurement. In contrast, the antibody titers in immunocompromised patients remained stable between the first and second measurements, but declined by the third. A two-way ANOVA revealed that time was a more significant factor than immunocompromised status for the declines in antibody titers.

Conclusions: In patients aged 12-25 years with underlying diseases, antibody titers in immunocompromised patients after SARS-CoV-2 vaccination were lower than in immunocompetent patients in the early post-vaccination period, but they maintained titers similar to the immunocompetent counterpart during the long-term follow-up.