No correlation between nasal viral load and severity of COVID-19 in large vaccine studies

An open-access paper published in JAMA Network Open this week is notable for not finding any correlation between SARS-CoV-2 viral load in the nasopharynx and subsequent severity of COVID-19.

These are unexpected results – other studies have linked viral load to severity of symptoms – suggest caution in interpreting individual-level viral load as a surrogate for COVID-19 severity, especially given increasing diversity in preexisting immunity.

This was a secondary analysis using data from the placebo participants in the four main international registrational vaccine studies. The results might be related to early timing of samples and/or sample sites compared to viral load in plasma.

The main significant association was a lower nasal viral load (by 0.5 log copies/mL) in the Janssen study, although this could have been linked to differences in sample collection and handling compared to other RCTs.

Fisher LH et al. SARS-CoV-2 viral load in the nasopharynx at time of first infection among unvaccinated individuals: A secondary cross-protocol analysis of 4 randomized trials. JAMA Netw Open. 20247(5):e2412835. (24 May 2024).
doi:10.1001/jamanetworkopen.2024.1283.