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by johnisgood
1651 days ago
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> Vaccination reduces the risk of delta variant infection and accelerates viral clearance. Nonetheless, fully vaccinated individuals with breakthrough infections have peak viral load similar to unvaccinated cases and can efficiently transmit infection in household settings, including to fully vaccinated contacts. Host–virus interactions early in infection may shape the entire viral trajectory. https://www.thelancet.com/journals/laninf/article/PIIS1473-3... |
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A few months after the second dose, 2 doses of the mRNA vaccines is insufficient to reduce peak viral load for breakthrough infections by the delta variant of the virus, making the vaccine less effective over time at preventing basic transmission and mild illness (the 2-dose vaccine was more effective with previous variants). However, a booster dose seems to make a significant improvement:
> By analyzing viral loads of over 16,000 infections during the current, Delta-variant-dominated pandemic wave in Israel, we found that BTIs in recently fully vaccinated individuals have lower viral loads than infections in unvaccinated individuals. However, this effect starts to decline 2 months after vaccination and ultimately vanishes 6 months or longer after vaccination. Notably, we found that the effect of BNT162b2 on reducing BTI viral loads is restored after a booster dose. These results suggest that BNT162b2 might decrease the infectiousness of BTIs even with the Delta variant, and that, although this protective effect declines with time, it can be restored, at least temporarily, with a third, booster, vaccine dose.
https://www.nature.com/articles/s41591-021-01575-4
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For the omicron variant, there is still further reduced effectiveness of these vaccines on basic transmission and mild illness (only 70% effectiveness after a 3 shots; I don’t think there’s much data yet about viral loads), though protection against severe illness should still be robust (but reliable data about this will not be available for another few weeks or months).