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COVID-19 vaccination effectiveness rates by week and sources of bias: a retrospective cohort study.

Anna OstropoletsGeorge Hripcsak
Published in: BMJ open (2022)
For vaccine effectiveness studies, observational data need to be scrutinised to ensure compared groups exhibit similar health-seeking behaviour and are equally likely to be captured in the data. While we found that studies may be capable of accurately estimating long-term effectiveness despite bias in early weeks, the early week results should be reported in every study so that we may gain a better understanding of the biases. Given the difference in temporal trends of vaccine exposure and patients' baseline characteristics, indirect comparison of vaccines may produce biased results.
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