Risk of hospital admission and death from first-ever SARS-CoV-2 infection by age group during the Delta and Omicron periods in British Columbia, Canada

Ratio of Infections to COVID-19 Cases and Hospitalizations in the United States based on SARS-CoV-2 Seroprevalence Data, September 2021-February 2022

Background

Understanding the risk of hospitalization from severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections can guide effective public health interventions and severity assessments. This study calculated infection-hospitalization ratios (IHRs) and infection-case ratios (ICRs) to understand the relationship between SARS-CoV-2 infections, cases, and hospitalizations among different age groups during periods of Delta and Omicron variant predominance.

Methods

After calculating antinucleocapsid SARS-CoV-2 antibody seroprevalence using residual commercial laboratory serum specimens, 2 ratios were computed: (1) IHRs using coronavirus disease 2019 hospitalization data and (2) ICRs using Centers for Disease Control and Prevention surveillance data. Ratios were calculated across age groups (0-17, 18-49, 50-69, and ≥70 years) for 2 time periods (September-December 2021 [Delta] and December 2021-February 2022 [Omicron]).

Results

Pediatric IHRs increased from 76.7 during Delta to 258.4 during Omicron. Adult IHRs ranged from 3.0 (≥70 years) to 21.6 (18-49 years) during Delta and from 10.0 (≥70 years) to 119.1 (18-49 years) during Omicron. The pediatric ICR was lower during the Delta period (2.7) compared with the Omicron period (3.7). Adult ICRs (Delta: 1.1 [18-49 years] to 2.1 [70+ years]; Omicron: 2.2 [>70+ years] to 2.9 [50-69 years]) were lower than pediatric ICRs during both time periods.

Conclusions

All age groups exhibited a lower proportion of infections associated with hospitalization in the Omicron period than the Delta period; the proportion of infections associated with hospitalization increased with each older age group. A lower proportion of SARS-CoV-2 infections were associated with reported cases in the Omicron period than in the Delta period among all age groups.

Kinetics of pro- and anti-inflammatory spike-specific cellular immune responses in long-term care facility residents after COVID-19 mRNA primary and booster vaccination: a prospective longitudinal study in Japan

BACKGROUND

The magnitude and durability of cell-mediated immunity in older and severely frail individuals following coronavirus disease 2019 (COVID-19) vaccination remain unclear. A controlled immune response could be the key to preventing severe COVID-19; however, it is uncertain whether vaccination induces an anti-inflammatory cellular immune response. To address these issues, a 48-week-long prospective longitudinal study was conducted. A total of 106 infection-naive participants (57 long-term care facility [LTCF] residents [median age; 89.0 years], 28 outpatients [median age; 72.0 years], and 21 healthcare workers [median age; 51.0 years]) provided peripheral blood mononuclear cell (PBMC) samples for the assessment of spike-specific PBMC responses before primary vaccination, 24 weeks after primary vaccination, and three months after booster vaccination. Cellular immune responses to severe acute respiratory syndrome coronavirus 2 spike protein were examined by measuring interferon (IFN)-γ, tumor necrosis factor (TNF), interleukin (IL)-2, IL-4, IL-6, and IL-10 levels secreted from the spike protein peptide-stimulated PBMCs of participants.

RESULTS

LTCF residents exhibited significantly lower IFN-γ, TNF, IL-2, and IL-6 levels than healthcare workers after the primary vaccination. Booster vaccination increased IL-2 and IL-6 levels in LTCF residents comparable to those in healthcare workers, whereas IFN-γ and TNF levels in LTCF residents remained significantly lower than those in healthcare workers. IL-10 levels were not significantly different from the initial values after primary vaccination but increased significantly after booster vaccination in all subgroups. Multivariate analysis showed that age was negatively associated with IFN-γ, TNF, IL-2, and IL-6 levels but not with IL-10 levels. The levels of pro-inflammatory cytokines, including IFN-γ, TNF, IL-2, and IL-6, were positively correlated with humoral immune responses, whereas IL-10 levels were not.

CONCLUSIONS

Older and severely frail individuals may exhibit diminished spike-specific PBMC responses following COVID-19 vaccination compared to the general population. A single booster vaccination may not adequately enhance cell-mediated immunity in older and severely frail individuals to a level comparable to that in the general population. Furthermore, booster vaccination may induce not only a pro-inflammatory cellular immune response but also an anti-inflammatory cellular immune response, potentially mitigating detrimental hyperinflammation.

2023/24 mid-season influenza and Omicron XBB.1.5 vaccine effectiveness estimates from the Canadian Sentinel Practitioner Surveillance Network (SPSN)

The Canadian Sentinel Practitioner Surveillance Network reports mid-season 2023/24 influenza vaccine effectiveness (VE) of 63% (95% CI: 51-72) against influenza A(H1N1)pdm09, lower for clade 5a.2a.1 (56%; 95% CI: 33-71) than clade 5a.2a (67%; 95% CI: 48-80), and lowest against influenza A(H3N2) (40%; 95% CI: 5-61). The Omicron XBB.1.5 vaccine protected comparably well, with VE of 47% (95% CI: 21-65) against medically attended COVID-19, higher among people reporting a prior confirmed SARS-CoV-2 infection at 67% (95% CI: 28-85).