The US Centers for Disease Control and Prevention (CDC) has recommended certain immunocompromised individuals and people over the age of 50 to get another mRNA Covid-19 booster at least 4 months after receiving an initial booster dose.

The move will increase protection for these vulnerable groups against severe disease from Covid-19, Xinhua news agency quoted the CDC as saying.

The CDC's move came right after the US Food and Drug Administration authorised a second booster dose of either the Pfizer-BioNTech or the Moderna Covid-19 vaccines for these people earlier on Tuesday.

In addition, the CDC said adults who received a primary vaccine and booster dose of Johnson & Johnson's Janssen Covid-19 vaccine at least 4 months ago may now receive a second booster dose using an mRNA Covid-19 vaccine.

During the recent Omicron surge, those who were boosted were 21 times less likely to die from Covid-19 compared to those who were unvaccinated, and 7 times less likely to be hospitalised, according to the CDC.