Description of Hospitalizations due to the SARS-CoV-2 Omicron Variant Based on Vaccination Status

Second Boost of Omicron SARS-CoV-2 S1 Subunit Vaccine Induced Broad Humoral Immune Responses in Elderly Mice

Currently approved COVID-19 vaccines prevent symptomatic infection, hospitalization, and death from the disease. However, repeated homologous boosters, while considered a solution for severe forms of the disease caused by new SARS-CoV-2 variants in elderly individuals and immunocompromised patients, cannot provide complete protection against breakthrough infections. This highlights the need for alternative platforms for booster vaccines. In our previous study, we assessed the boost effect of the SARS-CoV-2 Beta S1 recombinant protein subunit vaccine (rS1Beta) in aged mice primed with an adenovirus-based vaccine expressing SARS-CoV-2-S1 (Ad5.S1) via subcutaneous injection or intranasal delivery, which induced robust humoral immune responses (1). In this follow-up study, we demonstrated that a second booster dose of a non-adjuvanted recombinant Omicron (BA.1) S1 subunit vaccine with Toll-like receptor 4 (TLR4) agonist RS09 (rS1RS09OM) was effective in stimulating strong S1-specific immune responses and inducing significantly high neutralizing antibodies against the Wuhan, Delta, and Omicron variants in 100-week-old mice. Importantly, the second booster dose elicits cross-reactive antibody responses, resulting in ACE2 binding inhibition against the spike protein of SARS-CoV-2 variants, including Omicron (BA.1) and its subvariants. Interestingly, the levels of IgG and neutralizing antibodies correlated with the level of ACE2 inhibition in the booster serum samples, although Omicron S1-specific IgG level showed a weaker correlation compared to Wuhan S1-specific IgG level. Furthermore, we compared the immunogenic properties of the rS1 subunit vaccine in young, middle-aged, and elderly mice, resulting in reduced immunogenicity with age, especially an impaired Th1-biased immune response in aged mice. Our findings demonstrate that the new variant of concern (VOC) rS1 subunit vaccine as a second booster has the potential to offer cross-neutralization against a broad range of variants and to improve vaccine effectiveness against newly emerging breakthrough SARS-CoV-2 variants in elderly individuals who were previously primed with the authorized vaccines.

Responses to Common Misconceptions Relating to COVID-19 Variant-Adapted mRNA Vaccines

The evolution of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and the waning of immunity over time has necessitated the use of booster doses of original coronavirus disease 2019 (COVID-19) vaccines. This has also led to the development and implementation of variant-adapted messenger RNA (mRNA) vaccines that include an Omicron sub-lineage component in addition to the antigen based on the wild-type virus spike protein. Subsequent emergence of the recombinant XBB sub-lineages triggered the development of monovalent XBB-based variant-adapted mRNA vaccines, which are available for vaccination campaigns in late 2023. Misconceptions about new variant-adapted vaccines may exacerbate vaccine fatigue and drive the lack of vaccine acceptance. This article aims to address common concerns about the development and use of COVID-19 variant-adapted mRNA vaccines that have emerged as SARS-CoV-2 has continued to evolve.

Distinct Clinical Presentations and Outcomes of Hospitalized Adults with the SARS-CoV-2 Infection Occurring during the Omicron Variant Surge

The COVID-19 Omicron variant has imposed a tremendous burden on healthcare services. We characterized the types of the Omicron variant-associated hospitalizations and their associations with clinical outcomes. Consecutive adults hospitalized with COVID-19 during the Omicron variant surge period of 1-14 January 2022, were classified into one of three groups based on their clinical presentations on admission: Group 1-primary COVID-19; Group 2-extrapulmonary manifestations of COVID-19; and Group 3-incidental COVID-19. Of the 500 patients who were hospitalized, 51.4% fell into Group 1, 16.4% into Group 2, and 32.2% into Group 3. The patients in Groups 1 and 2 were older, with higher proportions of comorbidities than patients in Group 3. The Group 1 patients had the highest mortality rate (15.6%), followed by Group 2 (8.5%), and Group 3 (0.6%), with adjusted odds ratios (OR) of 22.65 (95% confidence interval [CI], 2.75-239.46; p = 0.004) and 10.95 (95% CI, 1.02-117.28; p = 0.048), respectively, compared to Group 3. Those in Group 1 showed a greater utilization of intensive care services (15.9%), followed by Group 2 (10.9%), and Group 3 (2.5%), with adjusted ORs of 7.95 (95% CI, 2.52-25.08; p < 0.001) and 5.07 (95% CI, 1.34-19.15; p = 0.017), respectively, compared to Group 3. The patients in Groups 1 and 2 had longer hospitalization stays than the patients in Group 3 (p < 0.001 and p = 0.002, respectively). Older age (≥65 years) was an independent factor associated with longer hospital stays (OR = 1.72, 95% CI, 1.07-2.77). These findings can help hospitals prioritize patient care and service planning for future SARS-CoV-2 variants.

Outcomes of Elderly Patients Hospitalized with the SARS-CoV-2 Omicron B.1.1.529 Variant: A Systematic Review

The Omicron (B.1.1.529) variant of the severe acute respiratory syndrome Coronavirus 2 (SARS-CoV-2) had an increased rate of spreading among the general population. Although this virus mutation resulted in milder symptoms, those on the vulnerable side of the population are still in danger of developing severe symptoms. Thus, this systematic review focused on identifying the clinical outcomes of older age patients (>65) that are hospitalized with the SARS-CoV-2 Omicron variant. The research was conducted using four electronic databases (PubMed, Scopus, Web of Science, and ProQuest Central), with a search query in December 2022 that comprised the duration of the COVID-19 pandemic. The inclusion criteria comprised (1) a population of patients older than 65 years, (2) a history of hospitalization for SARS-CoV-2 infection, and (3) infection with Omicron B.1.1.529 variant. The initial search generated 295 articles, out of which six were included in the systematic review, and a total of 7398 patients. The main findings were that when looking at the elderly population, the mortality and hospitalization rates remained high. This is because older people are more vulnerable and have more comorbidities that interfere with the virus's progress. However, there is inconsistency in mortality rates, since the data reported by the included studies had different selection criteria based on the severity of the COVID-19 infection. Although no statistically significant differences were found between the unvaccinated and vaccinated groups, patients who got booster doses of vaccination had a lower likelihood of developing severe symptoms, serving as a protective factor for this population.