Impact of SARS-CoV-2 Delta and Omicron variants on viral burden and cycle threshold in BNT162b2-vaccinated 12–18 years group

The SARS-CoV-2 pandemic continues to impact the medical, economic, social, and political areas worldwide. Although it has been claimed that children are the most responsible for the outbreaks as of September 2021, the statistics showed controversary. Although it showed no difference in viral load and Ct values between symptomatic children and symptomatic adults, or between asymptomatic children and asymptomatic adults, the molecular mechanism remains unclear. Here, we aimed to investigate the effects of different strains on infection by comparing viral load levels in pediatric patients aged 12–18 years, infected with different variants of SARS-CoV-2, and vaccinated with full-dose BNT162b2. In this retrospective study, a total of 200 patients aged 12–18 years, who were diagnosed with COVID-19 in our hospital, and vaccinated with full-dose BNT162b2, were analyzed according to their gender, age, viral load, and cycle threshold values. Viral RNA levels were evaluated using Ct values, a semi-quantitative proxy of viral load. While the findings did not show a significant difference between gender and age (P = 0.886 and P = 0.897, respectively), a significant difference was found between the Ct and viral load (P < 0.0001). In conclusion, SARS-CoV-2 viral load was higher in cases infected with SARS-CoV-2 Delta variant than SARS-CoV-2 Omicron variant (mean Ct = 23.05 ± 4.06, viral load = 7.8 × 105 copies/ml and mean Ct = 28.04 ± 3.02, viral load = 7.8 × 103 copies/ml, respectively). These findings indicated that the Delta variant had high viral load and our result could be one of the causes the Delta variant was more effective in the pandemic severity than the other variants in the October–December periods when the Delta variant was dominant in Northern Cyprus. During the same period, the severity of the disease was higher, with higher hospitalization and death rates.