Viral load dynamics of SARS-CoV-2 in the moderately symptomatic COVID-19 patients in Dak Lak, Viet Nam, 2021

COVID-19 vaccines reduce infection, disease severity, and death by SARS-CoV-2 by reducing viral load. This study aimed to evaluate the change of cycle threshold (Ct) value in COVID19 patients and investigate factors related to the Ct value change on the 3rd (D3), 7th (D7), 10th (D10), and 14th (D14) day after hospital admission in Dak Lak in 2021. Nasopharyngeal swabs and serum samples were obtained from 251 COVID-19 patients. Samples were collected on D3, D7, D10, and D14 after hospital admission and tested for SARS-CoV-2 by real-time RT-PCR tests. Ct values were categorized as high viral load, moderate viral, and low viral load. Electrochemiluminescence immunoassay was used to estimate the anti-SARS-CoV-2 antibodies. The results demonstrated that vaccinated individuals against COVID-19 have a faster rate of hospital discharge than the unvaccinated group, most clearly on D10. The Ct change on D10 of vaccinated individuals was statistically significantly higher (1.35 times) than of unvaccinated individuals (P < 0.01). The mean Ct values of unvaccinated individuals on D3, D7, D10, and D14 were lower than that of vaccinated individuals. However, there was a statistically significant increase in Ct of vaccinated individuals compared to unvaccinated individuals only on D10 and D14 (P < 0.03). The percentage of Ct value >= 30 and negative of vaccinated persons on D7 (60.9%) was similar to that of unvaccinated persons on D10 (59.4%) (P > 0.05). Vaccinated individuals at hospital admission with Ct <= 20 on D1 had a statistically significant decline in viral load on D10 and D14, 1.55 and 1.30 times higher compared to unvaccinated individuals (P < 0.05). The percentage of Ct >= 30 was significantly higher in males than females, especially on D7 and D14 with PR = 1.26 and 1.11 (P < 0.05). In conclusion, individuals vaccinated against COVID-19 had reduced transmission by a significant decline in viral load and recovered faster than unvaccinated individuals.