There wasn't a set of unvaccinated health care workers as a control so the science doesn't prove that TLDR. The fact that there was no severe symptoms is encouraging though.

I'm also very happy that studies like this are being done. We need a whole lot more studies looking at this, long term immunity with B and T-cells, and comparing neutralizing antibody levels between vaccinated and unvaccinated who have been infected but show little or no symptoms.