Regulators in the United States have authorised another COVID-19 booster shot for people aged 50 and older, amid concerns that coronavirus infections may begin rising again due to waning immunity to Omicron variants.

The US Food and Drug Administration’s (FDA) decision on Tuesday allows a fourth dose of the Pfizer or Moderna vaccines to be administered at least four months after the previous dose.

COVID-19 cases in the US have dropped sharply since a record surge in January, but have seen a small uptick during the past week, according to data from the US Centers for Disease Control and Prevention (CDC).