Waning of humoral immunity depending on the types of COVID-19 vaccine

Background: There are limited data on the rates of the waning of antibody levels after two-dose and booster vaccination according to the different platforms of COVID-19 vaccines. Methods: We enrolled healthcare workers (HCWs) in a tertiary care hospital who received homologous two-dose vaccination, followed by a homologous or heterologous booster mRNA vaccine. SARS-CoV-2 S1-specific IgG was measured using ELISA. A linear mixed regression model was used to compare the slope from the peak antibody titer to the lowest antibody titers 3 months after vaccination. Results: A total of 113 HCWs (BNT162b2 (n=48 [42%]), ChAdOx1 nCoV-19 (n=52 [46%]) or mRNA-1273 (n=13 [12%])) were enrolled in this prospective cohort study. More gradual antibody waning was observed over 3 months with the two-dose ChAdOx1 nCoV-19 (ChAdOx1) than with the two-dose BNT162b2 or mRNA-1273 (p< 0.001 and p=0.001, respectively). In addition, homologous mRNA-1273 booster induced a more durable antibody response than homologous BNT162b2 booster (p< 0.001) or heterologous ChAdOx1-BNT162b2 booster (p< 0.001). Conclusion: 2-dose homologous ChAdOx1 vaccination or homologous mRNA-1273 booster appears to induce more-durable antibody responses than 2-dose homologous mRNA vaccination, homologous BNT162b2 booster, or 2-dose ChAdOx1 followed by BNT162b2 booster. Disclosures: All Authors: No reported disclosures.

Clinical scoring system to predict viable viral shedding in patients with COVID-19

Background. Centers for Disease Control and Prevention (CDC) recommends 5 to 20 days of isolation for COVID-19 patients depending on symptom duration and severity regardless of genomic PCR results or vaccination history. However, in real clinical practice, more individualized approach is required. We thus developed clinical scoring system to predict viable viral shedding in a given patient by using various factors affecting viable viral shedding. Methods. We prospectively enrolled adult patients with SARS-CoV-2 infection admitted to tertiary hospital and day care center between February 2020 and January 2022. The daily dense respiratory sampling (i.e. saliva, sputum, or nasopharyngeal swabs) during the hospital and day care center stay were obtained. Genomic RNA viral load and viral culture were performed for these samples. Clinical predictors of negative viral culture results were identified using survival analysis and multivariable analysis. Results. A total of 612 samples from 121 patients of varying degrees of severity were obtained. Of these, 494 (81%) samples were saliva, 63 (10%) were nasopharyngeal swab, and the remaining 55 (9%) were sputum. Of these 612 specimens, 154 (25%) samples revealed positive viral culture results. Univariate and multivariable Cox's time varying proportional hazard model revealed that symptom onset day, viral copy number, disease severity, organ transplant recipient, gender, and vaccination status were independently associated with viral culture results. We thus developed the 5-factor model from -3 to 3 points: viral copy number (-3 to 3 points depending on copy number), disease severity (1 point to moderate to critical diseases), organ transplant recipient (2 points), gender (-1 points to male), and vaccination status (-2 points to fully vaccinated status). The predictive culture-negative rates were calculated through the symptom onset day and the score of the day the sample was collected. Conclusion. Our clinical scoring system can provide objective probability of negative culture results in a given COVID-19 patient with genomic viral load, and appears to be useful to decide de-isolation policy depending on individualized factors associated with viable viral shedding beyond simple symptom-based isolation strategy by CDC.