The review, published in The Lancet, summarizes the currently available evidence from randomized controlled trials and observational studies published in peer-reviewed journals and pre-print servers.

A consistent finding from the observational studies is that vaccines remain highly effective against severe disease, including that from all the main viral variants. Averaging the results reported from the observational studies, vaccination had 95% efficacy against severe disease both from the delta variant and from the alpha variant, and over 80% efficacy at protecting against any infection from these variants. Across all vaccine types and variants, vaccine efficacy is greater against severe disease than against mild disease (see figure, page 2).

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