Effectiveness of COVID-19 vaccine in reducing viral load and transmission

Below you will find a summary of the article “Association Between SARS-CoV-2 Viral Load and COVID-19 Vaccination in 4 Phase 3 Trials”, published in the September 2024 issue of Infectious diseases by Janes et al.

COVID-19 vaccines have been shown to reduce severe disease and death, as well as transmission of the virus, as measured by SARS-CoV-2 viral load (VL).

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

They measured a reduction in viral load of 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, −0.01 to 0.47; n = 916 placebo, 424 vaccine).

They concluded that vaccines were effective in reducing transmission of SARS-CoV-2 in the early phase of the pandemic, when the original strain was dominant.

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