Austrian national registry data covering the whole adult population with no documented prior SARS-CoV-2 infection were used to compare mortality between vaccinated and unvaccinated people, adjusting for age, sex, long-term care allowance and education. Vaccinated individuals had lower all-cause mortality irrespective of dose number, with adjusted hazard ratios of 0.38 to 0.52 in the quarter after each vaccination was introduced and 0.24 to 0.32 in the two weeks after a dose in the matched analysis. Cancer mortality and deaths from external causes followed the same pattern, causes that vaccination cannot plausibly influence.
Why it is interesting: It puts a national-scale figure on the selection bias that inflates observational estimates of COVID-19 vaccine effectiveness, and shows it is largest in exactly the window such studies use.