They don't know if they have mass infections, because they don't test. Continuing your line of thought we could deduce that North Korea or Turkmenistan(NK v 2.0) don't have cases at all. They didn't test after all

It's not a coincidence that when f.e Bangladesh or Djibouti started testing more they saw rapid raise in number of cases. It's also not a coincidence that countries, which have high numbers are those, which test a lot.

​

Many developing countries are likely in an earlier stage of the development of pandemy than those in Europe/US, but they don't have resources to do much about controlling the virus.

This sub preaches "test more", but countries, which do only a handful of tests are somehow doing an amazing job, just because their numbers are the result of no testing.

​

And speaking of Vietnam. I don't neccessarily question that they dealt with the epidemy, because they have good history of this.

Although I would be careful about unquestionably believing in information given, by a country, which regularly places near the bottom of every list about freedom of speech, press etc.