Little information is available for antibody levels against SARS‐CoV‐2 variants of concern induced by Omicron breakthrough infection and a third booster with an inactivated vaccine (InV) or Ad5‐nCoV in people with completion of two InV doses. Plasma was collected from InV pre‐vaccinated Omicron‐infected patients (OIPs), unvaccinated OIPs between 0 and 22 days, and healthy donors (HDs) 14 days or 6 months after the second doses of an InV and 14 days after a homogenous booster or heterologous booster of Ad5‐nCoV. Anti‐Wuhan‐, Anti‐Delta‐, and Anti‐Omicron‐receptor binding domain (RBD)‐IgG titers were detected using enzyme‐linked immunosorbent assay. InV pre‐vaccinated OIPs had higher anti‐Wuhan‐, anti‐Delta‐, and anti‐Omicron‐RBD‐IgG titers compared to unvaccinated OIPs. Anti‐Wuhan‐RBD‐IgG titers sharply increased in InV pre‐vaccinated OIPs 0–5 days postinfection (DPI), while the geometric mean titers (GMTs) of anti‐Delta‐ and anti‐Omicron‐RBD‐IgG were 3.3‐fold and 12.0‐fold lower. Then, the GMT of anti‐Delta‐ and anti‐Omicron‐RBD‐IgG increased to 35 112 and 28 186 during 11–22 DPI, about 2.6‐fold and 3.2‐fold lower, respectively, than the anti‐Wuhan‐RBD‐IgG titer. The anti‐Wuhan‐, anti‐Delta‐, and anti‐Omicron‐RBD‐IgG titers declined over time in HDs after two doses of an InV, with 25.2‐fold, 5.6‐fold, and 4.5‐fold declination, respectively, at 6 months relative to the titers at 14 days after the second vaccination. Anti‐Wuhan‐, anti‐Delta‐, and anti‐Omicron‐RBD‐IgG titers elicited by a heterologous Ad5‐nCoV booster were significantly higher than those elicited by an InV booster, comparable to those in InV pre‐vaccinated OIPs. InV and Ad5‐nCoV boosters could improve humoral immunity against Omicron variants. Of these, the Ad5‐nCoV booster is a better alternative.
BackgroundA third mRNA vaccine booster is recommended to improve immunity against SARS-CoV-2 in kidney transplant recipients (KTRs). However, the immunity against SARS-CoV-2 Ancestral strain and Delta and Omicron variants elicited by the third dose of inactivated booster vaccine in KTRs remains unknown.MethodsThe blood parameters related to blood cells count, hepatic function, kidney function, heart injury and immunity were explored clinically from laboratory examinations. SARS-CoV-2 specific antibody IgG titer was detected using an enzyme-linked immunosorbent assay. Cellular immunity was analyzed using interferon-γ enzyme-linked immunospot assay.ResultsThe results showed that there were no severe adverse effects and apparent changes of clinical laboratory biomarkers in KTRs and healthy volunteers (HVs) after homologous inactivated vaccine booster. A third dose of inactivated vaccine booster significantly increased anti-Ancestral-spike-trimer-IgG and anti-Ancestral-receptor binding domain (RBD)-IgG titers in KTRs and HVs compared with the second vaccination. However, the anti-Delta-RBD-IgG and anti-Omicron-RBD-IgG titers were significantly lower than anti-Ancestral-RBD-IgG titer in KTRs and HVs after the third dose. Notably, only 25.6% (10/39) and 10.3% (4/39) of KTRs had seropositivity for anti-Delta-RBD-IgG and anti-Omicron-RBD-IgG after booster, which were significantly lower than HVs (anti-Delta-RBD-IgG: 100%, anti-Omicron-RBD-IgG: 77.8%). Ancestral strain nucleocapsid protein and spike specific T cell frequency after booster was not significantly increased in KTRs compared with the second dose, significantly lower than that in HVs. Moreover, 33.3% (12/36), 14.3% (3/21) and 14.3% (3/21) of KTRs were positive for the Ancestral strain and Delta and Omicron spike-specific T cells, which were significantly lower than HVs (Ancestral: 80.8%, Delta: 53.8%, and Omicron: 57.7%).ConclusionsA third dose of inactivated booster vaccine may significantly increase humoral immunity against the Ancestral strain in KTRs, while humoral and cellular immunity against the Delta and Omicron variants were still poor in KTRs.
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