Safety and antibody responses to inactivated COVID-19 vaccines among elderly patients with COPD: a prospective cohort study

Background Elderly patients with chronic obstructive pulmonary disease (COPD) are at increased risk of severe coronavirus disease 2019 (COVID-19) outcomes. We aimed to assess the safety and longitudinal antibody dynamics of a three-dose schedule of the inactivated COVID-19 vaccine (Vero cell, Covilo) in elderly patients with COPD. Methods This prospective cohort study enrolled 410 COPD patients (aged≥60), 80 younger healthy controls (HCs, 18–59 years), and 108 older HCs (≥60 years) in Zhejiang Province, China. COPD patients received a three-dose regimen (Day 0, 21, and 111), while HCs received a standard two-dose series. Neutralizing antibodies (NAbs), anti-receptor-binding domain IgG (anti-RBD IgG), and anti-spike & nucleocapsid IgG (anti-S&N IgG) were measured at five time points to evaluate the immunogenicity. Safety was assessed within 7 days after each dose and throughout follow-up. Results The overall incidence of adverse events in COPD patients was 10.24%, predominantly mild (Grade 1), with decreasing frequency across doses. After the two-dose primary series, NAbs seroconversion rates at 28–35 days were comparable between COPD patients (60.19%) and HCs (63.64%–66.67%). However, antibody concentration declined markedly within three months, particularly for NAbs. Strong positive correlations were observed among NAbs, anti-RBD IgG, and anti-S&N IgG (Spearman’s ρ = 0.754–0.905; p< 0.001). A third dose administered after approximately three months significantly increased NAbs seroconversion rate to 83.50% and markedly elevated antibody concentrations to 207.22 U/mL. Despite the booster, NAbs declined significantly six months after the third dose. Conclusions A three-dose regimen of Covilo is safe and effectively elicits antibody responses in elderly COPD patients. However, the rapid waning of antibody levels suggests a need for optimized booster strategies to maintain long-term protection in this vulnerable group.