COVID-19 vaccination is associated with reduced transmission of SARS-CoV-2, new research suggests

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According to an article published in the New England Journal of Medicine, both the BNT162b2 and ChAdOx1 nCoV-19 vaccines are associated with reduced onward transmission of SARS-CoV-2, compared with unvaccinated people.

The retrospective analysis included 146,243 tested contacts of 108,498 index patients. The researchers investigated the vaccination status of index patients and contacts and how this was associated with onward transmission of the virus. They also determined how these associations varied between the alpha and delta variants and the time since the second vaccination.

In vaccinated index patients who became infected with the alpha variant, the results showed that two vaccinations with either BNT162b2 or ChAdOx1 were independently associated with reduced polymerase chain reaction test positivity in contacts (adjusted rate ratio [aRR] with BNT162b2 0.32; 95% confidence interval [CI] 0.21–0.48, and ChAdOx1 0.48; 95% CI 0.30–0.78), compared with no vaccination. Reductions in transmission of the delta variant were smaller.

Reductions in transmission of the delta variant were greater after two BNT162b2 vaccinations (aRR compared with no vaccination 0.50; 95% CI 0.39–0.65) than two ChAdOx1 vaccinations (aRR 0.76; 95% CI 0.70–0.82).

Vaccination was associated with higher cycle-threshold values—meaning lower viral loads—of the alpha variant and, to a smaller extent, of the delta variant.

This article originally appeared on Univadis, part of the Medscape Professional Network.


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