I think you misread an article. I saw one mention that 20% decline the infection rate. That's entirely different than herd immunity. I don't see any article say

I think you misread an article. I saw one mention that 20% decline the infection rate. That's entirely different than herd immunity. I don't see any article saying that the mentioned countries have hit herd immunity. Especially New Zealand seems questionable, they've gone to a full lockdown, not for herd immunity.