The US Food and Drug Administration (FDA) has amended the emergency use authorisations of the Moderna and Pfizer-BioNTech Covid-19 bivalent mRNA vaccines, approving a second dose of the updated Covid-19 booster for older adults and people with weakened immune systems.

Those 65 and older can get a second dose of the updated versions of the Moderna and Pfizer-BioNTech booster at least four months following their initial bivalent dose, Xinhua news agency reported, citing a statement by the FDA.

Most people who are immunocompromised can get an additional updated booster dose at least two months following their last dose, according to the FDA.

Most unvaccinated individuals may receive a single dose of a bivalent vaccine, rather than multiple doses of the original monovalent mRNA vaccines.

The monovalent Moderna and Pfizer-BioNTech Covid-19 vaccines are no longer authorized for use in the US, said the FDA. [IANS/NS]