Omicron Variant Generates a Higher and More Sustained Viral Load in Nasopharynx and Saliva Than the Delta Variant of SARS-CoV-2

Abstract

The Omicron variant of SARS-CoV-2 spreads more easily than earlier variants, possibly as a result of a higher viral load in the upper respiratory tract and oral cavity. Hence, we investigated whether the Omicron variant generates a higher viral load than that of the Delta variant in saliva and nasopharynx. Both specimens were collected from 52 Omicron and 17 Delta cases at two time points one week apart and analyzed by qRT-PCR. Viral load was measured as 10 log RNA genome copies per 1000 human cells according to the WHO reference standard. We found that Omicron cases carried a higher viral load and had more sustained viral shedding compared to the Delta cases, especially in the nasopharynx.

Keywords: Delta variant; Norway; Omicron variant; SARS-CoV-2; viral load.

Figure 1

Viral load in nasopharyngeal swabs vs. saliva. (A,C): Correlation between viral load and days after symptom onset in NPS or saliva. Thick red/blue lines represent regression curves for the whole group (Delta or Omicron), whereas thin red/blue lines represent paired samples. (B,D): Viral load in NPS or saliva, shown as Tukey plots at inclusion (baseline) and one-week follow-up. Figure 1A,B was previously published in [6]. * p < 0.05 Omicron vs. Delta was adjusted for symptom duration.