The study from Qatar doesn't say how long after the first dose they tested Pfizer's COVID-19 vaccine. Protection usually starts after about 12 days.

A health worker applies a pad on the arm of a man after inoculating him against the coronavirus at a drive-through vaccination centre in the city of ...

https://www.businessinsider.com/quatar-real-world-data-suggests-two-doses-are-needed-against-variants-2021-5

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