Longitudinal monitoring of anti-SARS-CoV-2 RBD IgG antibodies after BNT162b2 vaccination in healthcare workers

In keeping with previous evidence from other countries, populations and settings (4,5), the results of this study on Italian healthcare workers who underwent administration of BNT162b2 mRNA-based COVID-19 vaccine suggest that humoral immunity and, more specifically, the serum levels of anti-SARS-CoV-2 RBD IgG antibodies, displayed a dramatic decay 6 months after vaccination, with values 95,3% lower than those measured at the peak, with nearly 30% of subjects displaying antibodies levels below the recommended threshold of positivity (i.e., <10 AU/mL). This data suggests that nearly one-third of BNT162b2 vaccine recipients have an insufficient value of serum anti-SARS-CoV-2 RBD IgG antibodies at 6 months post-vaccination. Intuitively, this finding goes hand in hand with the evidence that the rate of breakthrough SARS-CoV-2 infections in COVID-19 vaccine recipients increases over time and is strongly correlated with the level of anti-SARS-CoV-2 RBD IgG antibodies (10), as well as provides additional support to the importance of SARS-CoV-2 serologic monitoring before administration of vaccine boosters. This strategy would allow to timely identify those in whom the neutralizing antibodies have waned faster, have become more vulnerable to infection and disease, and shall hence be prioritized for receiving additional vaccine boosters in the future.