"The effectiveness of three dose vaccine regimens against covid-19 related death remains uncertain." - auch in einer Meta-Analyse mit insgesamt 100 Millionen (!) Studienteilnehmern...

Effectiveness of heterologous and homologous covid-19 vaccine regimens: living systematic review with network meta-analysis | The BMJ

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https://www.bmj.com/content/377/bmj-2022-069989