The outbreak was mostly in unvaccinated people, and there was no background of prior infections (they never had a first wave).

Besides, studies on healthcare workers, who are tested regularly, showed a clear reduction in transmission.

Which vaccine did they use? The CDC says the strongest evidence for preventing spread is for the mRNA vaccines.

The vaccine produced by China's Sinopharm company:

https://duckduckgo.com/?q=sinopharm+seychelles&t=fpas&ia=web

Not entirely accurate. From the top article in your search:

"Among the vaccinated population that has had two doses, 57 percent was given Sinopharm, while 43 percent was given AstraZeneca."