Authored by Eyal Shahar via The Brownstone Institute,
Each year the CDC publishes an estimate of the effectiveness of the flu vaccine in the previous flu season. Recently, the NIH director criticized the test-negative design from which the estimates are derived. He was right. The basic premise of the design is a two-edged sword: on the one hand, restricting the sample to people who sought medical care might reduce confounding by healthcare-seeking behavior; on the other hand, that restriction might add another type of bias - colliding bias - which is not as widely appreciated. The net bias remains unknown.
This, however, is not the only shortcoming of test-negative case-control studies of the flu vaccine. In this post, I will expose the shaky results of a large study of the flu vaccine in 2022-2023, when the vaccine was well-matched to the dominant strain. The study was based on the VISION Vaccine Effectiveness Network, o
