RESUMEN

COVID-19 mRNA vaccine BNT162b2 is highly immunogenic and effective, but recent studies have indicated waning anti-SARS-CoV-2 immune responses over time. Increasing infection rates has led authorities in several countries to initiate booster campaigns for vulnerable populations, including the elderly. However, the durability of vaccine-induced immunity in the elderly is currently unknown. Here, we describe interim results of a prospective cohort study comparing immune responses in a cohort of vaccinated elderly persons to those in healthcare workers (HCW), measured six months after first immunisation with BNT162b2. Anti-SARS-CoV-2 S1-, full Spike- and RBD-IgG seropositivity rates and IgG levels at six months were significantly lower in the elderly compared to HCW. Serum neutralization of Delta VOC measured by pseudovirus neutralisation test was detectable in 43/71 (60.6%, 95%CI: 48.9-71.1) in the elderly cohort compared to 79/83 in the HCW cohort (95.2%, 95%CI: 88.3-98.1) at six months post vaccination. Consistent with the overall lower antibody levels, SARS-CoV-2-S1 T cell reactivity was reduced in the elderly compared to HCW (261.6 mIU/ml, IQR:141.5-828.6 vs 1198.0 mIU/ml, IQR: 593.9-2533.6, p<0.0001). Collectively, these findings suggest that the established two-dose vaccination regimen elicits less durable immune responses in the elderly compared to young adults. Given the recent surge in hospitalisations, even in countries with high vaccination rates such as Israel, the current data may support booster vaccinations of the elderly. Further studies to determine long-term effectiveness of COVID-19 vaccines in high-risk populations and the safety and effectiveness of additional boosters are needed.