[orforforof]

According to Table 2 their sample had 8,199 unvaccinated and 9,269 vaccinated. It seems odd that more cases were found in the vaccinated people, can anyone suggest why? Statistical anomaly?

Edit: I misread the table, I thought column 1 was number of subjects. The replies explain well why the # of cases would be larger for the (larger) vaccinated population.

[akrito]

It's because many more people are vaccinated. Assume 100,000 people are vaccinated and 10,000 aren't. If the infection rate in vaccinated population is 5%, and in the unvaccinated population is 50%, then out of 10,000 infected people, 5,000 will be vaccinated and 5,000 won't.

[landemva]

A couple years ago vaccines prevented almost all people from getting sick. Not anymore.

[sdenton4]

Consider the extremal point: If 100% of people are vaccinated, then all cases are breakthrough cases, and 0% of cases will be in unvaccinated people. At some point, the raw count of breakthrough cases crosses over and exceeds the raw count of unvaccinated cases. This doesn't mean the vaccine is ineffective, of course!