New formulations should aim to produce antibody responses to the XBB.1.5 or XBB.1.16 variants, the advisory group said, adding that other formulations or platforms that achieve neutralizing antibody responses against XBB lineages could also be considered.

The group suggested no longer including the original COVID-19 strain in future vaccines, based on data that the original virus no longer circulates in human beings and shots targeting the strain produce "undetectable or very low levels of neutralizing antibodies" against currently circulating variants.

COVID-19 vaccine makers like Pfizer/BioNtech (PFE.N), , Moderna Inc (MRNA.O) and Novavax Inc (NVAX.O) are already developing versions of their respective vaccines targeting XBB.1.5 and other currently circulating strains.

The U.S. Food and Drug Administration is also set to hold a meeting of outside experts in June to discuss the strain compositions of COVID-19 shots for later this year; vaccine manufacturers will be expected to update their shots once the strains are selected.

The bivalent booster shots developed and distributed last year targeted two different strains - the Omicron variant as well as the original virus.

WHO's advisory group, which recommends if changes are needed to the composition of future COVID-19 shots, said currently approved vaccines should continue to be used in accordance with the agency's recommendations.

In late March, WHO had revised its COVID vaccination recommendations and suggested healthy children and adolescents might not necessarily need a shot, but older and high-risk groups should get a booster between six and 12 months after their last vaccine.

The latest recommendations come about two weeks after WHO ended the global emergency status for COVID-19.