section_path: Strategies/Herd immunity
section_name: Herd immunity
paragraph_text: Herd immunity
  
  In July 2021, several experts expressed concern that achieving herd immunity may not be possible because Delta can transmit among vaccinated individuals. CDC published data showing that vaccinated people could transmit Delta, something officials believed was less likely with other variants. Consequently, WHO and CDC encouraged vaccinated people to continue with non-pharmaceutical interventions such as masking, social distancing, and quarantining if exposed.