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The latest Omicron sub-variants -- including the BA.4 and BA.5 forms causing new global surges in infections -- are even better at eluding vaccines and most antibody treatments than previous variants, finds a study.

Subvariants BA.2.12.1, BA.4, and BA.5 are rapidly expanding worldwide, with BA.4/5 now making up more than 50 per cent of new Covid cases in the US. These sub-variants are thought to be even more transmissible than prior Omicron sub-variants, owing to several new mutations in spike proteins.

"The virus is continuing to evolve, as expected, and it is not surprising that these new, more transmissible sub-variants are becoming more dominant around the world," said David D. Ho, director of the Aaron Diamond AIDS Research Center at Columbia University.

"Understanding how currently available vaccines and antibody treatments stand up to the new sub-variants is critical to developing strategies to prevent severe disease, hospitalisations, and deaths -- if not infection," Ho added.

In laboratory experiments, Ho and his team studied the ability of antibodies from individuals who received at least three doses of an mRNA vaccine, or got two shots and were then infected with Omicron, to neutralise the new sub-variants.

The study, published in Nature, revealed that while BA.2.12.1 is only modestly more resistant than BA.2 in individuals who were vaccinated and boosted, BA.4/5 was at least four times more resistant than its predecessor.

In addition, the scientists tested the ability of 19 monoclonal antibody treatments to neutralise the variants and found that only one of the available antibody treatments remained highly effective against both BA.2.12.1 and BA.4/5.

"Our study suggests that as these highly transmissible sub-variants continue to expand around the globe, they will lead to more breakthrough infections in people who are vaccinated and boosted with currently available mRNA vaccines," Ho said.

Though the current study suggests that the new variants may cause more infections in vaccinated individuals, the vaccines continue to provide good protection against severe disease.

"Efforts to develop new vaccine boosters aimed at BA.4/5 may improve protection against infection and severe disease," Ho said.