Coronavirus disease is a new virus that has never infected humans before. Humans have no immunity against it, so the virus spreads quickly. Herd immunity occurs when at least 70%-90% of a population have been infected and developed natural immunity…
Coronavirus disease is a new virus that has never infected humans before. Humans have no immunity against it, so the virus spreads quickly. Herd immunity occurs when at least 70%-90% of a population have been infected and developed natural immunity…