Covid-19 vaccine booster jabs will be offered to "all Americans" from 20 September, according to US officials.
The jabs will first be given to healthcare workers, nursing home residents and older people who were vaccinated at least eight months ago.
The White House says the initiative is a response to rising infections from the Delta variant and evidence that the protectiveness of the vaccines fades.
A final decision still requires approval and a formal recommendation.
Daily cases in the United States have soared since early July. At the time, there were fewer than 10,000 cases and now there are more than 150,000 across the nation.
Hospitals are stretched thin and the death rates in many states have led officials to re-instate mask mandates and social distancing protocols.
The heads of the Centers for Disease Control and Prevention, the Food and Drug Administration, the National Institutes of Health and President Joe Biden's chief medical adviser, Dr Anthony Fauci, are all in agreement on the need for a booster vaccine.
It will be up to these groups to approve the White House's plan.
The effectiveness of the Covid vaccine is now known to decrease over time, officials say, "and in association with the dominance of the Delta variant, we are starting to see evidence of reduced protection against mild and moderate disease".
"We conclude that a booster shot will be needed to maximize vaccine-induced protection and prolong its durability."
The booster will be made available to Americans who received their second shot of the Pfizer or Moderna vaccine eight months ago. The White House said they anticipate that people who received Johnson & Johnson's single-dose Covid vaccine will also need boosters, but more research is needed.
In recent weeks, several other countries such as Israel, France and Germany have decided to offer boosters to older adults as well as people with weak immune systems.
However, the World Health Organization recently called for a pause on booster jabs until at least the end of September - or when more of the populations in lower-income nations receive at least their first round of vaccines.
More than one million Americans had independently sought an extra vaccine dose before the official decision on boosters was announced, according to federal data.