A vial of the Pfizer-BioNTech Covid-19 vaccine, in Haxby, northern England on December 22, 2020. Image Credit: AFP

New York: US regulators authorised a second booster dose of Pfizer Inc and BioNTech SE's COVID-19 vaccine for people 50 and older due to concerns about waning immunity in the age group, the drugmakers said on Tuesday.

The US Food and Drug Administration also authorised the second booster dose of the vaccine for people aged 12 and older with compromised immune systems.

The new boosters - a fourth round of shots - to be administered at least four months after the third dose are intended to offer more protection against severe disease and hospitalization, the companies said.

The authorisation comes as some scientists have raised concerns about the highly contagious BA.2 Omicron subvariant, which has driven new spikes in COVID-19 cases in other countries.

COVID-19 cases in the United States have dropped sharply since a record surge in January, but have seen a small uptick over the past week, according to data from the U.S. Centers for Disease Control and Prevention.

"While this EUA (emergency use authorization) will help address a current need for some, we're working diligently to develop an updated vaccine that not only protects against current COVID-19 strains, but also provides more durable responses," Pfizer Chief Executive Albert Bourla said in a statement.

Pfizer and BioNTech originally asked for the next booster doses to be authorized for people 65 and older in a submission citing data collected in Israel, where a second booster is already authorized for many people over age 18. read more The companies did not explain why the age range had been expanded.

Scientists and officials have debated whether young, healthy people will need a fourth shot. A study of Israeli healthcare workers suggested that the fourth dose added little additional protection in the age group.

Biden administration officials have said that the US government currently has enough doses of the vaccines to meet the demand for another round of booster shots in older Americans, even as funding for the U.S. pandemic response has all but run out.

They say that unless Congress approves more spending, the government will not be likely to be able to be pay for future inoculations, if they are needed, particularly if the vaccines need to be redesigned to target new variants.