The US Food and Drug Administration (FDA) has authorized the administration of the fourth dose of Pfizer and Moderna brand COVID-19 vaccines for people aged 50 years and over.
Previously, the fourth dose was only allowed for people aged 12 years and over who have a poor immune system.
The US Centers for Disease Control and Prevention (CDC) will now consider how to apply the FDA authorization.
People who want to get a second booster dose can only do so at least four months after the first booster dose, the FDA said Tuesday (29/3).
The FDA authorization comes as COVID-19 cases in the US have been declining after a winter spike caused by the omicron variant.
However, a new subvariant called BA.2 has spread in Europe and the US.
About two-thirds of Americans are fully vaccinated, meaning they have been vaccinated twice with a dose of Pfizer or Moderna, or once with a dose of Johnson & Johnson. Only half have been vaccinated with the booster.
While the vaccine has not stopped the widespread spread of omicron, health officials say it helps those infected avoid serious illness or death.
The government is also considering granting a fourth dose to all citizens in the fall, when the number of cases could rise again. [rd/lt]