Recent news, North Korea has a disease outbreak it hasn't explicitly labeled COVID. That may be because of distrust of the outside world. But that wouldn't explain why Kim Jong Un has not yet accepted much help from China.
Also possible, North Korea may simply not have the testing capability to precisely diagnose. But if Kim Jong Un distrusts external diagnostic technology, he may for the same reason be suspicious of non-North Korean vaccine.
The downside is obvious. Perhaps the silver lining in this nation-sized gray cloud is if North Korea goes without COVID vaccine, the rest of the world may gain insight into the affect on a population of millions in the COVID pandemic, denied vaccination.