"CDC continues to encourage the 47 million adults who are not yet vaccinated to get vaccinated as soon as possible to protect themselves, their families, loved ones and communities," the CDC said in a statement on Friday.
This recommendation makes it clear that every adult should or may get a booster six months after finishing the first two doses, unlike the previous one only suggesting boosters to people aged 65 year and older, and to certain adults at high risk of infection or of severe disease, Xinhua news agency reported.
Several CDC advisers said they hoped the simpler age-based guidelines would ease some of the confusion around who is eligible for the extra shots.
On Friday, the US Food and Drug Administration authorised boosters of the Pfizer/BioNTech and Moderna Covid-19 vaccines for everyone aged 18 years and over.
As of Friday, 229,291,004 people have received at least one dose of Covid-19 vaccine, making up 69.1 per cent of the whole US population; fully vaccinated people stood at 195,920,566, accounting for 59 per cent of the total. A total of 33,454,832 people, or 17.1 per cent of the fully vaccinated group, have received booster shots, according to CDC data.