ABSTRACT
BACKGROUND: In December 2021, Omicron replaced Delta as the dominant coronavirus disease 2019 (COVID-19) variant in Thailand. Both variants embody diverse epidemiological trends and immunogenicity. We investigated whether Delta and Omicron patients' biological and clinical characteristics and immunogenicity differed post-COVID-19 infection. METHODS: This retrospective cohort study investigated the clinical outcomes and laboratory data of 5181 patients with mild-to-moderate COVID-19 (Delta, 2704; Omicron, 2477) under home isolation. We evaluated anti-receptor-binding domain immunoglobulin G (anti-RBD IgG) and surrogate viral neutralizing (sVNT) activity in 495 individuals post-COVID-19 infection during the Delta pandemic. RESULTS: Approximately 84% of all patients received favipiravir. The median cycle threshold (Ct) values were lower for Omicron patients than Delta patients (19 vs. 21; p < 0.001), regardless of vaccination status. Upper respiratory tract symptoms were more frequent with Omicron patients than Delta patients. There were no significant associations between Ct and Omicron symptoms (95% confidence interval 0.98-1.02). A two-dose vaccine regimen reduced hospital readmission by 10% to 30% and death by under 1%. Anti-RBD IgG and sVNT against Delta were higher among older individuals post-COVID-19 infection. Older individuals expressed anti-RBD IgG and sVNT for a more extended period after two-dose vaccination than other age groups. CONCLUSIONS: After a full vaccination course, breakthrough mild-to-moderate Delta and Omicron infections have limited immunogenicity. Prior infections exert reduced protection against later reinfection or infection from novel variants. However, this protection may be sufficient to prevent hospitalization and death, particularly in countries where vaccine supplies are limited.
ABSTRACT
The coronavirus disease 2019 pandemic has affected nearly 70% of children and teenagers around the world due to school closure policies. School closure is implemented widely in order to prevent viral transmission and its impact on the broader community, based on preliminary recommendations and evidence from influenza. However, there is debate with regard to the effectiveness of school closures. Growing evidence suggests that a child's SARS-CoV-2 infection is often mild or asymptomatic and that children may not be major SARS-CoV-2 transmitters; thus, it is questionable if school closures prevent transmission significantly. This question is important as a majority of children in low- and middle-income countries depend on free school meals; unexpected long-term school closure may adversely impact nutrition and educational outcomes. Food insecurity is expected to be higher during the pandemic. In this viewpoint, we argue for a more thorough exploration of potential adverse impacts of school closures in low- and middle-income countries and recommend actions to ensure that the health and learning needs of vulnerable populations are met in this time of crisis.