SARS-CoV-2 Antibody Response against Mild-to-Moderate Breakthrough COVID-19 in Home Isolation Setting in Thailand

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.

Immune response after SARS-CoV-2 infection with residual post COVID symptoms

“…Analyses considered viral load for comparisons of Ct values by vaccine exposure groups and self-reported symptoms as previously described. 6…”

“…06S600), SARS-CoV-2 IgG II Quant for use with ARCHITECT; Abbott Laboratories, USA) as described previously. 6 This assay linearly measures the antibody level between 21.0 - 80,000.0 arbitrary unit (AU)/mL, which was converted later to WHO International Standard concentration as binding antibody unit per mL (BAU/mL) following the equation provided by the manufacturer (BAU/mL = 0.142 x AU/mL). The level greater or equal to the cutoff value of 50 AU/mL or 7.1 BAU/mL was defined as seropositive.…”

“…1 Most individuals with breakthrough SARS-CoV-2 infection can experience asymptomatic or mild-to-moderate-to-severe coronavirus disease 2019 (COVID-19). 6,7 A previous study 1 showed sera from BA.1 vaccine breakthrough infection exhibited significant reductions in neutralization against BA.5/BA.4; thereby, raising the possibility of Omicron reinfections.…”

“…Distinct immune dysregulation with lymphocytopenia, increased neutrophils and activation of the coagulation cascade have been described in the acute phase. 6,8 Following acute COVID-19 infection, 10-70% of COVID-19 patients reported physical and mental symptoms 2-3 months after infection. [9][10][11] Numbers of hospitalized symptomatic COVID-19 patients experienced LC symptoms.…”

Home Isolation and Online Support Strategies during Mild COVID-19 Pandemic Waves in Thailand: A Scoping Review

“…Our "home isolation" (HI) strategy and in vitro and in vivo studies demonstrated that the Omicron variant replicated well in the upper respiratory tract but was poorly involved in the lower respiratory tract [18], leading to higher transmissibility than the Delta variant. A body of evidence shows that breakthrough infections have still occurred since the Delta variant wave, increasing total daily confirmed cases, and that primary immunization with the current available approved vaccines provides limited protection against symptomatic disease due to the Omicron variant, so that a booster shot is indispensable [19,20]. Still, vaccination and prior infection have been documented to reduce COVID-19 transmission during an Omicron-predominant period, and additional doses of updated vaccination (bivalent vaccines) led to greater reductions in infectiousness, thereby providing additional protection against symptomatic new SARS-CoV-2 variant infection [21,22].…”