Transmission and viral load kinetics of the delta variant in the UK [pdf]

Study carried out in the UK in Sep-Oct 2021 with 602 community contacts of 471 COVID cases.

Findings:

- Being vaccinated reduces the rate of catching the delta variant from a household contact from 38% to 25%.

- Being vaccinated reduces the rate of trasmitting the delta variant to a household contact from 25% to 23%.

- Vaccination does not significantly change the peak viral load, but does correlate with faster viral load decline.

Interesting comparison with this study [0] from April - around the time that Delta was just beginning to spread in the UK [1] - which suggests that even a single dose of vaccine reduces the change of household transmission up to 50%.

My main takeaway: vaccination is less effective against delta, but still worth it.

[0] https://khub.net/documents/135939561/390853656/Impact+of+vac...

[1] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8349999/