Has the emergence of the Delta, or Indian, variant reduced the effectiveness of Covid vaccines and if so by how much? The fear that the Delta variant might be partially escaping our vaccines has often been expressed in recent weeks, especially given that highly-vaccinated countries such as Israel and parts of the US have suffered new peaks of infection since the Delta variant came to dominate. But there has been a lack of real-world data to prove whether or not there is any grounding to these fears.
Today, however, the Oxford University Covid 19 Infection Survey published a study which seeks to answer this question. It compared the results of PCR tests on over 700,000 people, around half of whom were swabbed between December 2020 and May 2021 when the Alpha (Kent) variant was dominant, and half of whom were swabbed between May and August 2021 when the Delta variant was dominant.
The study found that vaccinated people had higher viral loads during the Delta period compared with the earlier Alpha period
The study concludes that yes, there is a drop in effectiveness, but not by all that much.
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