The transmissibility of the Delta variant is almost as high as chickenpox, with each infected person, on average, infecting eight or nine others, according to the reports.
Fully vaccinated people can transmit the virus as well as unvaccinated people, it also said. Vaccination, however, provides substantial protection against the virus.
The disease control centre called for universal mask requirements and vaccination as the best tool against the Delta variant.
The United States is now experiencing a spike in COVID-19 cases, with the Delta strain accounting for over 80% of new infections as of July 20th. Some 70% of US adults, or 178 million, have received at least one dose of a COVID-19 vaccine and 60%, or 155 million, are fully vaccinated, according to the CDC.