The following is a summary of “Association Between SARS-CoV-2 Viral Load and COVID-19 Vaccination in 4 Phase 3 Trials,” published in the September 2024 issue of Infectious Disease by Janes et al.

COVID-19 vaccines have been proven to reduce severe illness, death, and viral transmission as measured by SARS-CoV-2 viral load (VL). 

Researchers conducted a retrospective study to evaluate the association between the COVID-19 vaccine and SARS-CoV-2 viral load during COVID-19 diagnosis in phase 3 randomized, placebo-controlled trials between July 2020 and July 2021.

They measured viral load reductions as 2.78 log₁₀ copies/mL (95% [CI], 1.38–4.18; n = 60 placebo, 11 vaccine) for NVX-CoV2373 and 2.12 log₁₀  copies/mL (95% CI, 1.44–2.80; n = 594 placebo, 36 vaccine) for mRNA-1273.

The results showed no significant associations for AZD1222 (0.59 log₁₀ copies/mL; 95% CI, −.19 to 1.36; n = 90 placebo, 78 vaccine) or Ad26.COV2.S (0.23 log₁₀ copies/mL; 95% CI, −.01 to .47; n = 916 placebo, 424 vaccine). 

They concluded vaccines effectively reduced SARS-CoV-2 transmission during the early stages of the pandemic when the ancestral strain was dominant.

Source: academic.oup.com/jid/advance-article-abstract/doi/10.1093/infdis/jiae400/7743415