Abstract
Studies comparing SARS-CoV-2 nasopharyngeal (NP) viral load (VL) according to virus variant and host vaccination status have yielded inconsistent results. We conducted a single center prospective study between July and September 2021 at the drive-through testing center of the Toulouse University Hospital. We compared the NP VL of 3775 patients infected by the Delta (n = 3637) and Alpha (n = 138) variants, respectively. Patient’s symptoms and vaccination status (2619 unvaccinated, 636 one dose and 520 two doses) were recorded. SARS-CoV-2 RNA testing and variant screening were assessed by using Thermo Fisher® TaqPath™ COVID-19 and ID solutions® ID™ SARS-CoV-2/VOC evolution Pentaplex assays. Delta SARS-CoV-2 infections were associated with higher VL than Alpha (coef = 0.68; p ≤ 0.01) independently of patient’s vaccination status, symptoms, age and sex. This difference was higher for patients diagnosed late after symptom onset (coef = 0.88; p = 0.01) than for those diagnosed early (coef = 0.43; p = 0.03). Infections in vaccinated patients were associated with lower VL (coef = −0.18; p ≤ 0.01) independently of virus variant, symptom, age and sex. Our results suggest that Delta infections could lead to higher VL and for a longer period compared to Alpha infections. By effectively reducing the NP VL, vaccination could allow for limiting viral spread, even with the Delta variant.
Highlights
The COVID-19 pandemic has recently been dominated by two major events: the emergence of more transmissible variants, and the acceleration of vaccination campaigns
We analyzed the results from 4245 SARS-CoV-2 infected patients; 3637 (85.7%) of them were infected with the Delta variant (median age: 26 years (20–35)) and 138 (3.3%) with the Alpha variant (median age: 26 years (21–36)) (Table 1)
The NP viral loads of unvaccinated patients infected with the Delta variant (median 7.1 log10 copies/mL (5.74–7.87)) were over 7 times greater than those of patients infected with the Alpha variant (median 6.21 (4.56–7.29)) (p < 0.0001) (Figure 1A)
Summary
The COVID-19 pandemic has recently been dominated by two major events: the emergence of more transmissible variants (variants of concern, VOC), and the acceleration of vaccination campaigns. The Delta variant spreads faster than the Alpha variant [1], may cause more severe disease [2] and may even be less sensitive to vaccines [3]. Previous studies, including ours, have described greater viral loads in patients infected with the Alpha variant than in other SARS-CoV-2 lineages, which could explain its greater transmissibility [5]. Few studies have compared the NP SARS-CoV-2 RNA loads of patients infected with Delta and Alpha variants or whether the NP viral load differs with the host vaccination status. There are conflicting data on the effectiveness of the vaccine in reducing the viral load of infected patients, depending on the virus variant involved [6,7]. The aim of this study was to independently evaluate the effect of the Delta variant and vaccination on the SARS-CoV-2 NP viral load
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