The sentence immediately before it provides important context as to what it's referring to:
> A substantial decline in immunity from mRNA vaccines 6-months post immunization has also been reported [9].
>Even though vaccinations offers protection to individuals against severe hospitalization and death, the CDC reported an increase from 0.01 to 9% and 0 to 15.1% (between January to May 2021) in the rates of hospitalizations and deaths, respectively, amongst the fully vaccinated [10].
It's referring to an increase in hospitalization/death 6 months after vaccination, compared to when you're first vaccinated. That's very very different from your statement that "countries with higher mRNA COVID vaccine coverage have (slightly) higher covid-mortality than countries with low/lower vaccine coverage".