Boosters were previously available to the immune compromised, over 65s, people at high risk of severe disease and people in high risk occupations.

The decision "helps to provide continued protection against Covid-19, including the serious consequences that can occur, such as hospitalization and death," said acting FDA commissioner Janet Woodcock.

"This emergency use authorization comes at a critical time as we enter the winter months and face increasing Covid-19 case counts and hospitalizations across the country," added Moderna CEO Stephane Bancel.

The FDA said it based its decision on strong immune response data from hundreds of people dosed with the two vaccines.

Pfizer's vaccine is dosed at 30 micrograms, the same as the primary series, while Moderna's is 50 micrograms, half the primary series -- but this was not cited by the FDA as data used to make its decision.

Pfizer also carried out a clinical trial involving 10,000 people aged over 16 which found the booster restored vaccine efficacy to 95 percent.

The Centers for Disease Control and Prevention will hold a meeting later Friday to discuss clinical recommendations for who should now seek a vaccine.

Both companies are conducting post authorization studies to assess the risks of myocarditis, or heart inflammation, which is more elevated in younger males.