Loss of Neutralizing Antibody Response to mRNA Vaccination against SARS-CoV-2 Variants: Differing Kinetics and Strong Boosting by Breakthrough Infection

Comparative Study on Two COVID-19 Outbreaks at a Long-Term Mental Health Facility in Korea in 2020 and 2022

(1) Background and Objectives: There were two distinct coronavirus disease 2019 (COVID-19) outbreaks in 2020 and 2022 at a long-term mental health facility (LTMHF) in Gyeonggi Province, Korea. We aimed to compare the two outbreaks and identify differences in epidemiological and clinical outcomes due to changes in epidemic timing and management methods. (2) Materials and Methods: The structural, operational, and case-specific LTMHF data of COVID-19-confirmed patients during these outbreaks in 2020 and 2022 were retrospectively analyzed. (3) Results: Forty individuals (37 residents) in 2020 and thirty-nine (32 residents) in 2022 were confirmed to have COVID-19, and ten were infected twice. Facility isolation was implemented as an infection control measure, and one COVID-19-related death occurred in 2020. All residents and staff were vaccinated at least twice in 2022; moreover, in 2022, 38 patients (97.4%) received a third vaccination less than months before infection. The average Ct value of the cases in 2022 was significantly higher than that in 2020; however, vaccine-breakthrough (V-BT) and reinfection after vaccination rates were similar. (4) Conclusions: COVID-19 vaccination could help lower the viral load of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which was inversely correlated with Ct values, and ventilation system improvements in health facilities might reduce transmissibility.

Boosting with Omicron-matched or historical mRNA vaccines increases neutralizing antibody responses and protection against B.1.1.529 infection in mice

The B.1.1.529 Omicron variant jeopardizes vaccines designed with early pandemic spike antigens. Here, we evaluated in mice the protective activity of the Moderna mRNA-1273 vaccine against B.1.1.529 before or after boosting with preclinical mRNA-1273 or mRNA-1273.529, an Omicron-matched vaccine. Whereas two doses of mRNA-1273 vaccine induced high levels of serum neutralizing antibodies against historical WA1/2020 strains, levels were lower against B.1.1.529 and associated with infection and inflammation in the lung. A primary vaccination series with mRNA-1273.529 potently neutralized B.1.1.529 but showed limited inhibition of historical or other SARS-CoV-2 variants. However, boosting with mRNA-1273 or mRNA-1273.529 vaccines increased serum neutralizing titers and protection against B.1.1.529 infection. Nonetheless, the levels of inhibitory antibodies were higher, and viral burden and cytokines in the lung were slightly lower in mice given the Omicron-matched mRNA booster. Thus, in mice, boosting with mRNA-1273 or mRNA-1273.529 enhances protection against B.1.1.529 infection with limited differences in efficacy measured.

Neutralization and Stability of SARS-CoV-2 Omicron Variant

The SARS-CoV-2 B.1.1.529/Omicron variant was first characterized in South Africa and was swiftly designated a variant of concern1. Of great concern is its high number of mutations, including 30-40 mutations in the virus spike (S) protein compared to 7-10 for other variants. Some of these mutations have been shown to enhance escape from vaccine-induced immunity, while others remain uncharacterized. Additionally, reports of increasing frequencies of the Omicron variant may indicate a higher rate of transmission compared to other variants. However, the transmissibility of Omicron and its degree of resistance to vaccine-induced immunity remain unclear. Here we show that Omicron exhibits significant immune evasion compared to other variants, but antibody neutralization is largely restored by mRNA vaccine booster doses. Additionally, the Omicron spike exhibits reduced receptor binding, cell-cell fusion, S1 subunit shedding, but increased cell-to-cell transmission, and homology modeling indicates a more stable closed S structure. These findings suggest dual immune evasion strategies for Omicron, due to altered epitopes and reduced exposure of the S receptor binding domain, coupled with enhanced transmissibility due to enhanced S protein stability. These results highlight the importance of booster vaccine doses for maintaining protection against the Omicron variant, and provide mechanistic insight into the altered functionality of the Omicron spike protein.