COVID-19 mRNA booster vaccination induces robust antibody responses but few adverse events among SARS-CoV-2 naïve nursing home residents

Abstract

Residents in nursing homes face heightened COVID-19 risks. We aimed to assess the adverse events (AEs) rates and antibody responses after the first to the fifth dose of COVID-19 mRNA vaccination in a nursing home cohort. Ninety-five SARS-CoV-2 naïve participants consisted of 26 staff (median age, 51 years) and 69 residents (median age, 88 years). Life-threatening AEs were reported in neither residents nor staff. The severity of non-life-threatening AEs was graded, and severe AEs were reported only in staff. The AEs rates were considerably lower in residents, compared to those in staff. Anti-RBD IgG and the neutralizing titers (NTs) against Wuhan and Omicron BA.4/BA.5 did not differ significantly between those with 'any AE' and 'no AE' among both staff and residents two months after the second, third and fifth doses, while the anti-RBD IgG significantly differed between two groups after third dose in residents. These findings suggest that the anti-RBD IgG and the NTs increase regardless of the occurrence of AEs. Our study underscores a robust antibody response in both in staff and residents, and fewer AEs following COVID-19 vaccination in SARS-CoV-2 naïve residents than staff, supporting the recommendation for mRNA booster doses in older adults at high-risk care facilities.

Keywords: COVID-19; Life-threatening adverse events; MRNA booster vaccination; Nursing home residents; Omicron variants; SARS-CoV-2.

Fig. 1

Genomic epidemiology and study design. Genomic epidemiology of SARS-CoV-2 variants or Omicron subvariants in Toyama Prefecture. Abbreviations: V2 + 2 M, V2 + 5 M; two or five months after the second dose of the vaccination (monovalent Wuhan), respectively, V3 + 2 M, V3 + 5 M; two or five months after the third dose of the vaccination (monovalent Wuhan), V5 + 2 M; two months after the fifth doses of the vaccination (bivalent Wuhan/BA.1- or Wuhan/BA.4/BA.5 adapted vaccine). Alpha; Alpha variant of SARS-CoV-2, Delta; Delta variant of SARS-CoV-2, BA1; Omicron BA.1 subvariant, BA.5; Omicron BA.5, XBB; Omicron XBB subvariant.

Fig. 2

Anti-RBD IgG Titers and NTs against Wuhan Strain, BA.1 or BA.4/BA.5 Subvariant after the Fifth Dose of BA.1 Bivalent Vaccine or BA.4/BA.5 Bivalent Vaccine in SARS-CoV-2 Naïve Staff and Residents. Anti-RBD IgG titers (a) and NTs against SARS-CoV-2pv (b) in SARS-CoV-2 naïve staff and residents, anti-RBD IgG titers following the fifth dose. The SARS-CoV-2 naïve staff and residents received the fifth dose of BA.1 bivalent vaccine (n = 1 and 21, respectively) or BA.4/BA.5 bivalent vaccine (n = 25 and 48, respectively). Each box includes the 25th and 75th percentiles with the median as thick line; bottom and upper whiskers respectively show the smallest and largest values. Dark gray and white boxes show staff and residents, respectively. Mann-Whitney U test, ***, p < 0.001; NS, not significant. Abbreviations: RBD, receptor-binding domain; NT, neutralizing titer, SARS-CoV-2, severe acute respiratory syndrome coronavirus 2; BTI, breakthrough infection; XBB; Omicron XBB 1.5 subvariant.

Fig. 3

Comparisons of the rate of AEs between SARS-CoV-2 Naïve staff and residents after the COVID-19 vaccinations. The rate of AEs of SARS-CoV-2 naïve staff (n = 26) (a) and residents (n = 69) (b) by vaccine dose was compared using the Chi-square test. The light gray, the medium gray, or the black bars denote the case with mild, moderate, or severe AE. The p-value of the Chi-square test for comparing of the rate of AEs between staff and residents is shown in (c). ***, p < 0.001; *, p < 0.05. Abbreviations: AE, adverse event, NS, not significant.

Fig. 4

Comparison of anti-RBD IgG, and NTs between SARS-CoV-2 Naïve Staff with ‘Any AE’ and ‘no AE’, and between SARS-CoV-2 Naïve residents with ‘Any AE’ and ‘no AE’ after COVID-19 Vaccination. Anti-RBD-IgG (a), NTs against Wuhan (b), Omicron BA.4/BA.5 (c), and XBB.1.5 (d) subvariants in staff and residents with ‘any AE’ and ‘no AE’. Each box includes the 25 th and 75 th percentiles with the median as thick line; bottom and upper whiskers respectively show the smallest and largest values. Closed and open boxes show ‘any AE’ and ‘no AE’, respectively. *, p < 0.05; NS, not significant as determined by the Mann-Whitney U test. Abbreviations: RBD, receptor-binding domain; V2 + 2 M, 2 months after the second dose of the vaccine; V3 + 2 M, 2 months after the third dose of the vaccine; V5 + 2 M, 2 months after the fifth dose of the vaccine; AE, adverse event.