The following is a summary of “Estimating the effect of COVID-19 vaccination and prior infection on Ct values as a proxy of SARS-CoV-2 viral load,” published in the December 2024 issue of Infectious Disease by Andeweg et al.
Researchers conducted a retrospective study to assess the effect of COVID-19 vaccination and prior infection status on RT-qPCR cycle threshold (Ct) values while considering the virus variant as a factor.
They used Dutch SARS-CoV-2 community testing data (n = 4,09,925 samples) from March 8, 2021, to December 31, 2022. Separate univariable linear regressions were performed for each explanatory variable, including age, sex, testing date, variant of infection, time since symptom onset, and testing laboratory. Causal inference analysis was then conducted to evaluate the impact of prior infection and vaccination status on Ct values, applying inverse propensity score weighting to adjust for confounders.
The results showed a negative correlation between age and Ct values. Modest differences in Ct values were observed across variants of infection, with Omicron variants showing lower Ct values (higher viral load) compared to earlier variants. The Ct values increased (indicating lower viral load) with prior infection. However, the effect of vaccination on Ct values was less significant.
Investigators concluded the prior infection was associated with higher Ct values, suggesting a potential decrease in viral load and potentially lower transmissibility.
Source: ijidonline.com/article/S1201-9712(24)00437-5/fulltext
