US drug regulators have approved applications by Moderna and BioNTech/Pfizer to release a Covid-19 vaccine that specifically targets the dominant strain of the Omicron variant.

The Food and Drug Administration on Wednesday gave the companies the go-ahead to roll out their “bivalent” shots, which target both the original strain of Covid and the fast-spreading BA.4 and BA.5 subvariants, ahead of a national booster programme this autumn.

US officials had previously resisted pushing ahead with variant-specific vaccines, but have been persuaded by the fact that many people with two or more shots are still susceptible to infection. They have taken this next step with the new vaccines despite a lack of clinical evidence about how they will work in an attempt to head off a huge spike in infections this winter.