It is interesting that none of the infection-recovered were infected - though with only 6 individuals, that could be luck. There have been other hints natural i

It is interesting that none of the infection-recovered were infected - though with only 6 individuals, that could be luck. There have been other hints natural immunity is stronger versus later variants. But your other point doesn't follow. The vaxed still tested positive at a slightly lower rate than the unvaxed. With no severe cases, no one died & no burden on limited emergency facilities was created. There's not enough info to know how much the vaxed spread it to others; they conjecture that their "patient 40", an unvaxed individual who had an asymptomatic case, was the "index case" that brought the infection in. Especially in the conditions of a mine – which might have limited ventiliation – perhaps that one unvaxed person shedded enough infectious material to create all the subsequent infections.