Vaccine effectiveness against delta and omicron variants of SARS-CoV-2

Never before had humanity seen such a swift, concerted response to the emergence of a lethal infectious disease as happened during the SARS-CoV-2 pandemic. Scientists, clinicians, publishers, the pharmaceutical industry, governments, and authorities allied to develop, approve, and roll-out targeted therapies and new vaccines within barely a year. As of 24 April 2023, more than 13.3 billion vaccine doses had been administered worldwide according to the World Health Organization.1The scientific community responded to the pandemic in an unprecedented way, but the continuously changing attributes of SARS-CoV-2 seemed to outpace their prevention and therapeutic strategies. Thousands of mutations occurred, some of which conferred a degree of immune escape, making early research findings about transmission dynamics and vaccine effectiveness more or less obsolete. The linked retrospective cohort study by Bohnert and colleagues (doi:10.1136/bmj-2022-074521),2 therefore, provides valuable new data about vaccine effectiveness in the periods when the delta (B.1.617.2) and omicron (B.1.1.529) were…
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