> The negative estimates in the final period arguably suggest different behaviour and/or exposure patterns in the vaccinated and unvaccinated cohorts causing underestimation of the VE. This was likely the result of Omicron spreading rapidly initially through single (super-spreading) events causing many infections among young, vaccinated individuals.

That's from the linked paper. The authors don't claim at all that the vaccine has negative efficacy, and the study is simply not set up to measure that anyway. You cannot draw this conclusion from the data in this paper.