Covid-19 vaccines are less effective against the delta variant, according to results in the U.K. from one of the largest real-world studies into the efficacy of the shots.
Pfizer Inc. and BioNTech SE’s messenger RNA vaccine lost effectiveness in the first 90 days after full vaccination, though that shot and the one made by AstraZeneca Plc still staved off a majority of Covid infections. When vaccinated people did get infected with delta, they were shown to have similar levels of virus in their bodies as those who hadn’t had shots. This suggests that vaccinating large portions of a population might not protect those who don’t get inoculated, casting doubt on the idea of achieving herd immunity.
