> Is it? According to who?

Medical advice was quite different between nations. Doctors and chief epidemiologists gave their advice, sometimes opposite advice to others, grounded in scientific beliefs that the individual held at the time. One of the biggest controversy and debates was the effectiveness of non-N95 surgical mask against airborne virus particles. Different studies gave different results, and depending on which culture, country and professional you asked you got different medical advice. It only got more muddled when it came to outdoor vs indoor.

That is just one example. It is well known in medical research that culture has a major impact on research findings and should not be overlooked. What is correct or incorrect is not obvious in a international context, and what help people in one place can be directly harmful in an other.