Leaving aside the fact that different countries are basically irrelevant here, what you are describing is a scientific consensus. These are always founded not on a single or even a handful of studies, but rather on many, many studies and mountains of evidence, meta-studies analyzing the studies, independent verification of results, and so forth. Science doesn't move forward by individual studies - that's a common misconception - it moves forward when enough of those studies accrue that a clear consensus emerges and shifts the prevailing paradigm. This is also why the lone brilliant genius who overturns everything with their piercing insight is such a stupid meme - even Einstein had to verify his results and wait for the rest of the community to double check his work.
And that's why it's a fallacy to place too much weight on a single study, and an even bigger fallacy to disregard places where there is, in fact, a clear consensus - e.g. cellphones don't cause cancer, global warming and evolution are real, etc...