This is utterly false. In fact, it has been proven to be highly successful in Brazil.
Sinovac vaccine restores a Brazilian city to near normal
Serrana saw vast improvements: Deaths fell by 95%, hospitalizations by 86% and symptomatic cases by 80%.
https://apnews.com/article/caribbean-brazil-coronavirus-pandemic-business-health-20bd94d28ac7b373d7a8f3f9c557e5b6
Like lots of people you seem to have a misunderstanding of what efficacy and effectiveness mean in regards to the Covid vaccine. They are mostly used to describe how well a vaccine works at suppressing any symptoms of Covid-19 no matter how trivial. But not about serious symptoms and mortality. As the study in Serrana showed, it provides very powerful protection against serious symptoms and death.
Granted, that this study was done before the advent of the Delta variant in Brazil. No one knows yet the level of protection provided by the Sinovac vaccine. Not epidemiologists, not virologists, and certainly not you. Studies are currently being done to determine its level of effectiveness including how well it reduces the severity of symptoms and the number of deaths.