Large-Scale Study of Antibody Titer Decay following BNT162b2 mRNA Vaccine or SARS-CoV-2 Infection

TLDR

Immune protection from SARS‑CoV‑2 vaccination or infection is believed to wane over time. The study aimed to characterize the kinetics of SARS‑CoV‑2 IgG antibodies after two doses of BNT162b2 vaccination or natural infection. Antibody titers were measured from 31 January to 31 July 2021 in 2,653 fully vaccinated and 4,361 unvaccinated convalescent individuals. Vaccinated individuals had higher initial IgG levels but experienced a faster decline, with titers dropping 38 % per month versus <5 % per month in convalescents, and 16.1 % of vaccinees fell below the seropositivity threshold at six months compared to 10.8 % of convalescents at nine months.

Abstract

Immune protection following either vaccination or infection with SARS-CoV-2 is thought to decrease over time. We designed a retrospective study, conducted at Leumit Health Services in Israel, to determine the kinetics of SARS-CoV-2 IgG antibodies following administration of two doses of BNT162b2 vaccine, or SARS-CoV-2 infection in unvaccinated individuals. Antibody titers were measured between 31 January 2021, and 31 July 2021 in two mutually exclusive groups: (i) vaccinated individuals who received two doses of BNT162b2 vaccine and had no history of previous infection with COVID-19 and (ii) SARS-CoV-2 convalescents who had not received the vaccine. A total of 2653 individuals fully vaccinated by two doses of vaccine during the study period and 4361 convalescent patients were included. Higher SARS-CoV-2 IgG antibody titers were observed in vaccinated individuals (median 1581 AU/mL IQR [533.8-5644.6]) after the second vaccination than in convalescent individuals (median 355.3 AU/mL IQR [141.2-998.7]; p < 0.001). In vaccinated subjects, antibody titers decreased by up to 38% each subsequent month while in convalescents they decreased by less than 5% per month. Six months after BNT162b2 vaccination 16.1% subjects had antibody levels below the seropositivity threshold of <50 AU/mL, while only 10.8% of convalescent patients were below <50 AU/mL threshold after 9 months from SARS-CoV-2 infection. This study demonstrates individuals who received the Pfizer-BioNTech mRNA vaccine have different kinetics of antibody levels compared to patients who had been infected with the SARS-CoV-2 virus, with higher initial levels but a much faster exponential decrease in the first group.