The US Centres for Disease Control and Prevention (CDC) has backed a booster shot of the Pfizer and BioNTech Covid-19 vaccine for Americans aged 65 and older, some adults with underlying medical conditions and some adults in high-risk working and institutional settings.

The move comes after an advisory panel to the agency did not recommend that people in high-risk jobs, such as teachers, and risky living conditions should get boosters. The panel had recommended boosters for the elderly and some people with underlying medical conditions.

CDC Director Rochelle Walensky said her agency had to make recommendations based on complex, often imperfect data.

"In a pandemic, even with uncertainty, we must take actions that we anticipate will do the greatest good," she said in a statement.

Read the full Reuters story here.