Those vaccines are/were sterilizing, meaning the vaccinated person cannot carry or spread the illness after vaccination. Covid-19 Vaccines are non-sterilizing and only lessen-symptoms. As we can clearly see, vaccinated individuals still spread the virus. Not only that, but vaccinated individuals are an added evolutionary pressure for the virus, which causes the emergence of vaccine-evading variants. This means new variants can bubble up within vaccinated individuals, like we've seen with Omicron (and most likely the case for Delta as well).

Thanks!

This cannot be used as an argument against vaccination though. The same thing happens if the population has a high percentage of people who got sick with covid, except that in that case there is a much higher death toll.

It's not that simple. The Salk polio vaccine did not prevent infection/transmission, but remained highly effective at preventing disease.

The initial studies on vaccine efficacy were designed to study efficacy at preventing serious illness, not transmission. So it was not known at the time how effective the vaccines would be on that dimension. To answer these questions requires novel research, it is not settled, freshmen biology knowledge.