A fourth dose of the COVID-19 vaccine may not be as effective as expected, according to a recent peer-reviewed study.⁠
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The retrospective population-based observational study published in the European Journal of Clinical Investigation used national health data from the Austrian epidemiological reporting system, individual all-cause mortality data from Statistics Austria, and the national COVID-19 vaccine registry.⁠
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Researchers calculated COVID-19 deaths and SARS-CoV-2 infections from Nov. 1 to Dec. 31, 2022, in 3,986,312 individuals, comparing the outcomes of 281,291 who received four vaccine doses with 1,545,242 individuals who received three vaccine doses to determine relative efficacy.⁠