Mohammadhossein Khorraminejad-Shirazi
1,2,3 
, Sara Sadat Nabavizadeh
4 , Shiva Aminnia
2, Maryam Ahmadifar
1,2, Roham Borazjani
5, Erfan Sadeghi
6, Shabnam Izadpanah
7, Mina Heidari Esfahani
8, Maral Mokhtari
8,9* , Ahmad Monabati
1,8,9* 1 Department of Pathology, School of Medicine, Shiraz University of Medical Sciences, Shiraz, Iran
2 Student Research Committee, Shiraz University of Medical Sciences, Shiraz, Iran
3 Cell and Molecular Medicine Student Research Group, School of Medicine, Shiraz University of Medical Sciences, Shiraz, Iran
4 Otolaryngology Research Center, Department of Otolaryngology, Shiraz University of Medical Sciences, Shiraz, Iran
5 Trauma Research Center, Shahid Rajaee (Emtiaz) Trauma Hospital, Shiraz University of Medical Sciences, Shiraz, Iran
6 Research Consultation Center (RCC), Shiraz University of Medical Sciences, Shiraz, Iran
7 Shiraz Transplant Center, Abu-Ali Sina Hospital, Shiraz University of Medical Sciences, Shiraz, Iran
8 Raz Pathobiology and Genetic Laboratory, Shiraz, Iran
9 Pathology Department, Shahid Faghihi Hospital, Shiraz University of Medical Sciences, Shiraz, Iran
Abstract
Background: The effect of vaccination on the SARS-CoV-2 baseline viral load and clearance during COVID-19 infection is debatable. This study aimed to assess the effects of demographic and vaccination characteristics on the viral load of SARS-CoV-2.
Methods: We included the patients referred for outpatient SARS-CoV-2 qRT-PCR (reverse transcriptase quantitative polymerase chain reaction) test between July and September 2022. Cycle threshold (Ct) data were compared based on the demographic and vaccination characteristics. A generalized linear model was used to determine the factors associated with the SARS-CoV-2 PCR Ct value.
Results: Of 657 participants, 390 (59.4%) were symptomatic and 308 (47.1%) were COVID-19 positive. Among 590 individuals with known vaccination status, 358 (60.6%) were booster vaccinated, 193 (32.6%) were fully vaccinated, 13 (2.2%) were partially vaccinated, and 26 (4.4%) were unvaccinated. Most vaccinated patients received inactivated vaccines (70.5%). The median Ct value was 20 [IQR: 18–23.75] with no significant difference between individuals with different vaccination statuses (P value = 0.182). There were significant differences in Ct value in terms of both symptom presence and onset (both P values < 0.001). Our regression model showed that inactivated vaccines (P value = 0.027), mRNA vaccines (P value = 0.037), and the presence and onset of symptoms (both P values < 0.001) were independent factors significantly associated with the viral load.
Conclusion: The SARS-CoV-2 baseline viral load is unaffected by vaccination status, yet vaccination might accelerate viral clearance. Furthermore, we demonstrated that the presence and onset of symptoms are independent variables substantially associated with the patient’s viral load.