The Delta COVID-19 strain spreads as easily as chickenpox, with fully vaccinated people also transmitting the virus, The Washington Post has reported, citing an internal document from the US Centers for Disease Control and Prevention (CDC), expected to be published later on Friday.

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 document.

Fully vaccinated people can transmit the virus as well as unvaccinated people, it also said. Vaccination, however, provides substantial protection against the virus, the document added.

The disease control center 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.