The US Food and Drug Administration on Friday said it has recommended that Covid-19 vaccine manufacturers make single-strain booster shots for this fall that would target the currently circulating Omicron subvariant XBB.1.5.

“Based on the totality of the evidence, FDA has advised manufacturers who will be updating their COVID-19 vaccines, that they should develop vaccines with a monovalent XBB 1.5 composition,” the agency said in a news release.

This single-strain – or, monovalent – vaccine would drop protection against the original strain of the virus that emerged in China in late 2019, a version that experts don’t expect to return and whose continued inclusion in vaccines may contribute to lower efficacy against newer strains.

Members of the FDA’s Vaccines and Related Biological Products Advisory Committee voted unanimously on Thursday that the new vaccine should protect against just one strain of the SARS-CoV-2 virus – a departure from the currently available bivalent vaccines.

The FDA advisory committee’s recommendation is in step with international guidance. The World Health Organization in May said that its advisory group recommended that updated vaccines target an XBB strain of the virus and leave out the original version.

Peter Marks, director of the FDA division that oversees vaccines, suggested at the committee meeting Thursday that the updated vaccines could be available around September, acknowledging that there is still some uncertainty around timelines. He noted that the FDA will need to work with the US Centers for Disease Control and Prevention to make a recommendation soon about whether eligible people should continue getting the currently available vaccines.

“FDA will continue to monitor the safety and effectiveness of the COVID-19 vaccines and the evolution of the SARS-CoV-2 virus,” the agency said in its statement.

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