I'm always so confused hearing people talk about their theories for why Asian countries performed so well in the coronavirus pandemic. The most confusing one is the argument that they have SARS/MERS cross-immunity.
SARS was a relatively controlled pandemic. There were 8,439 cases worldwide, predominantly in China, before the last chain of transmission was broken in July of 2003. Covid successes like South Korea, Thailand, and Vietnam had 3, 9, 63 cases respectively. The US had actually more than all three with 73 cases.
MERS likewise has been relatively contained. There have been about 2,566 cases globally. The majority of cases, 2,167, have been in Saudi Arabia where the virus is endemic. The US had 2.
In both cases underdetection was unlikely as they both were very lethal viruses.
People have peculiar notions of how widespread these viruses were. SARS was contained through dedicated mitigation, albeit it was a bit easier to detect and isolate cases than SARS-COV-2. And MERS has largely remained in KSA, aside from an outbreak in South Korea.