The US Centres for Disease Control and Prevention has recommended Americans choose to receive one of two other authorised Covid-19 vaccines over Johnson & Johnson's shot, due to rare but sometimes fatal cases of blood-clotting.

The CDC's move came after its Advisory Committee on Immunisation voted unanimously to make the recommendation in favour of the vaccines made by Moderna Inc and Pfizer /BioNTech over the J&J shot, Reuters reported.

Members of the panel also said J&J's vaccine is less effective in preventing Covid-19 than the other two authorised vaccines.