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The effectiveness of the Pfizer, Moderna and AstraZeneca vaccines declined after the Delta COVID-19 variant became predominant in the US, new data shows. The study looked at more than 150,000 cases of COVID-19 that occurred between May 1 2021, when Delta made up just 1.8 per cent of cases, through to the end of August when Delta made up more than 99 per cent of cases. It found that the effectiveness of all three vaccines declined from an average of 93.4 per cent to an average of 74.2 per cent over this time period. However, the good news is that all vaccines remained effective against hospitalisation, with no real change as Delta took hold with the exception of a small decline in effectiveness for mRNA vaccines in the over 65s.
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