Pronounced antibody elevation after SARS-CoV-2 BNT162b2 mRNA booster vaccination in nursing home residents

Abstract

Background: Infection control during COVID-19 outbreaks in nursing facilities is a critical public health issue. Antibody responses before and after the third (booster) dose of SARS-CoV-2 vaccination in nursing home residents have not been fully characterized.

Methods: This study included 117 individuals: 54 nursing home residents (mean age, 83.8 years; 39 SARS-CoV-2-naive and 15 previously infected) and 63 healthcare workers (mean age, 45.8 years; 32 SARS-CoV-2-naive and 31 previously infected). Anti-spike (receptor-binding domain [RBD]) and anti-nucleocapsid antibody responses to BNT162b2 mRNA vaccination and their related factors were evaluated using pre- (shortly and 6 months after the second dose) and post-booster vaccination samples.

Results: The median anti-spike (RBD) IgG level in SARS-CoV-2-naive residents 6 months after the second dose was the lowest among the four groups, with a decreasing rate of over 90%. The median rate of increase before and after the third dose in SARS-CoV-2-naive residents was significantly higher than that in SARS-CoV-2-naive healthcare workers (64.1- vs. 37.0-fold, P = 0.003), with the highest level among the groups. The IgG ratio of SARS-CoV-2-naive residents to healthcare workers after the second and third doses changed from one-fifth (20%) to one-half (50%). The rate of increase after the third dose in previously infected individuals was three- to fourfold, regardless of residents or healthcare workers.

Conclusions: Advanced aged nursing home residents, poor responders in the initial SARS-CoV-2 vaccine series, could obtain sufficient antibody responses with the additional booster dose, despite more than 6 months after the second.

Keywords: COVID-19; SARS-CoV-2; antibody response; booster vaccination; nursing home residents.

FIGURE 1

Anti‐spike (RBD) IgG antibody levels shortly after the second dose, 6 months after the second dose, and shortly after the third dose of BNT162b2 mRNA vaccination in SARS‐CoV‐2‐naive and previously infected healthcare workers and nursing home residents. The white circles represent data of SARS‐CoV‐2‐naive healthcare workers (n = 32). The white triangles represent data of previously infected healthcare workers (n = 31). The black circles represent data of SARS‐CoV‐2‐naive residents (n = 39). The black triangles represent data of previously infected residents (n = 15). After, doses 2 and 3 indicate 21 days after each dose. Six months indicate 6 months after the second dose. The horizontal solid bars and numbers in each group represent the median values. The horizontal line represents the value of 4160 AU/mL, a threshold level indicating highly effective antibody neutralization. RBD, receptor‐binding domain; SARS‐CoV‐2, severe acute respiratory syndrome coronavirus 2; HCW, healthcare workers; NHR, nursing home residents

FIGURE 2

(A) Association of age with anti‐spike (RBD) IgG antibody levels after BNT162b2 mRNA vaccination. The white circles represent data of SARS‐CoV‐2‐naive healthcare workers. The white triangles represent data of previously infected healthcare workers. The black circles represent data of SARS‐CoV‐2‐naive nursing home residents. The black triangles represent data of previously infected residents. The horizontal line represents the value of 4160 AU/mL. (B) Decreasing rate of anti‐spike (RBD) IgG antibody levels at 6 months after the second dose of BNT162b2 mRNA vaccination. The rates (%) of reduction in the IgG levels between the two points of 21 days and 6 months after the second dose are shown. The horizontal solid bars and numbers in each group represent the median values. (C) Increasing rate of anti‐spike (RBD) IgG antibody levels before and after the third dose of BNT162b2 mRNA vaccination. The fold rates of increase in the IgG levels between the two points of 6 months after the second dose and 21 days after the third dose are shown. The horizontal solid bars and numbers in each group represent the median values. (D) Increasing rate of anti‐spike (RBD) IgG antibody levels between the second and third doses of BNT162b2 mRNA vaccination. The fold rates of change in the IgG levels between the two points of 21 days after the second and third doses are shown. The horizontal solid bars and numbers in each group represent the median values. RBD, receptor‐binding domain; SARS‐CoV‐2, severe acute respiratory syndrome coronavirus 2; HCW, healthcare workers; NHR, nursing home residents